A platform for building backends
Last updated 2 years ago by veryakov .
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$ cnpm install backendjs 
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Backend library for node.js

General purpose backend library. The primary goal is to have a scalable platform for running and managing node.js servers for Web services implementation.

This project only covers the lower portion of the Web services ecosystem: node.js processes, HTTP servers, basic API functinality, database access, caching, messaging between processes, metrics and monitoring, a library of tools for developing node.js servers.

For the UI and presentation layer there are no restrictions what to use as long as it can run on top of the Express server.


  • Exposes a set of Web service APIs over HTTP(S) using Express framework.
  • Database API supports Sqlite, PostgreSQL, MySQL, DynamoDB, Cassandra, MongoDB, Redis with all basic operations behaving the same way allowing to switch databases without changing the code.
  • Database drivers for LevelDB, LMDB, CouchDB, Riak, ElasticSearch support only a subset of all database operations
  • Database operations (Get, Put, Del, Update, Select) for all supported databases using the same DB API.
  • Easily extendable to support any kind of database, provides a database driver on top of Redis with all supported methods as an example.
  • Provides accounts, connections, locations, messaging and icons APIs with basic functionality for a qucik start.
  • Supports crontab and queue job processing by separate worker processes.
  • Authentication is based on signed requests using API key and secret, similar to Amazon AWS signing requests.
  • Runs web server as separate processes to utilize multiple CPU cores.
  • Supports WebSockets connections and process them with the same Express routes as HTTP requests
  • Supports several cache modes(Redis, Memcache, Hazelcast, LRU) for the database operations, multiple hosts support in the clients for failover.
  • Supports several PUB/SUB modes of operations using Redis, RabbitMQ, Hazelcast.
  • Supports async jobs processing using several work queue implementations on top of SQS, Redis, DB, RabbitMQ, Hazelcast.
  • ImageMagick as a separate C++ module for in-process image scaling, see bkjs-wand on NPM.
  • REPL(command line) interface for debugging and looking into server internals.
  • Supports push notifications for mobile devices, APN and GCM/FCM.
  • Supports HTTP(S) reverse proxy mode where multiple Web workers are load-balanced by the proxy server running in the master process instead of relying on the OS scheduling between processes listening on the same port.
  • Can be used with any MVC, MVVC or other types of frameworks that work on top or with the Express server.
  • AWS support is very well integrated including EC2, S3, DynamoDB, SQS and more.
  • Includes simple log watcher to monitor the log files including system errors.
  • Supports i18n hooks for request/response objects, easily overriden with any real i18n implementation.
  • Integrated very light unit testing facility which can be used to test modules and API requests
  • Support runtime metrics about the timing on database, requests, cache, memory and request rate limit control
  • Hosted on github, BSD licensed.

Check out the Documentation for more details.


To install the module with all optional dependencies if they are available in the system

npm install backendjs

This may take some time because of downloading and compiling required dependencies like ImageMagick. They are not required in all applications but still part of the core of the system to be available once needed.

To install from the git

 npm install git+

or simply

 npm install vseryakov/backendjs

Quick start

  • Simplest way of using the backendjs, it will start the server listening on port 8000

      $ node
      > var bkjs = require('backendjs')
      > bkjs.server.start()
  • Access is allowed only with valid signature except urls that are exlicitely allowed without it (see api-allow config parameter below)

  • Same but using the helper tool, by default it will use embedded Sqlite database and listen on port 8000.

      bkjs web
  • To start the server and connect to the DynamoDB (command line parameters can be saved in the etc/config file, see below about config files)

      bkjs web -db-pool dynamodb -db-dynamodb-pool default -aws-key XXXX -aws-secret XXXX
  • If running on EC2 instance with IAM profile then no need to specify AWS credentials:

      bkjs web -db-pool dynamodb -db-dynamodb-pool default
  • or to the PostgreSQL server, database backend

      bkjs web -db-pool pgsql -db-pgsql-pool postgresql://postgres@
  • All commands above will behave exactly the same

  • Tables are not created by default, in order to initialize the database, run the server or the shell with -db-create-tables flag, it is called only inside a master process, a worker never creates tables on start

    • prepare the tables in the shell

      bksh -db-pool pgsql -db-pgsql-pool postgresql://postgres@ -db-create-tables
    • run the server and create tables on start

      bkjs web -db-pool pgsql -db-pgsql-pool postgresql://postgres@ -db-create-tables
  • While the local backendjs is runnning, the documentation is always available at http://localhost:8000/doc.html (or whatever port is the server using)

  • To add users from the command line

      bksh -account-add login test secret test name TestUser email
  • By default no external modules are loaded so it needs the accounts module with a parameter -allow-modules PATTERN, this will load all modules that match the pattern, default modules start with bk_:

      bkjs web -allow-modules bk_
  • To start node.js shell with backendjs loaded and initialized, all command line parameters apply to the shell as well

      ./ -shell
  • To access the database while in the shell

      >"bk_account", {}, function(err, rows, info) { console.log(err, rows) });
      >"bk_account", {}, lib.log);
      > db.add("bk_account", { login: 'test2', secret: 'test2', name' Test 2 name', gender: 'f' }, lib.log);
      >"bk_account", { gender: 'm' }, lib.log);

To run an example

  • Go to examples/api directory:

  • Run the application, it will start the Web server on port 8000:

  • Now login with the new account,

  • Go to http://localhost:8000/api.html and click on Login at the top-right corner, then enter 'test' as login and 'test' as secret in the login popup dialog.

  • To see your account details run the command in the console /account/get

  • To see current metrics run the command in the console /system/stats/get

  • To see charts about accumulated metrics go to http://localhost:8000/metrics.html

  • When the web server is starte with -watch parameters any change in the source files will make the server restart automatically letting you focus on the source code and not server management, this mode is only enabled by default in development mode, check for parameters before running it in the production.


Almost everything in the backend is configurable using a config files, config database or DNS. The whole principle behind it that once deployed in production, even quick restart are impossible to do so there should be a way to push config changes to the processes without restarting.

Every module defines a set of config parameters that defines the behavior of the code, due to single threaded nature of the node.js, it is simple to update any config parameter to a new value so the code can operate differently. To achieve this the code must be written in a special way, like driven by configuration which can be changed at any time.

All configuration goes through the configuration process that checks all inputs and produces valid output which is applied to the module variables. Config file or database table with configuration can be loaded on demand or periodically, for example all local config files are watched for modification and reloaded automaticlaly, the config database is loaded periodically which is defined by another config parameter.

Backend runtime

When the backendjs server starts it spawns several processes that perform different tasks.

There are 2 major tasks of the backend that can be run at the same time or in any combination:

  • a Web server (server) with Web workers (web)
  • a job scheduler (master)

These features can be run standalone or under the guard of the monitor which tracks all running processes and restarted any failed ones.

This is the typical output from the ps command on Linux server:

ec2-user    891  0.0  0.6 1071632 49504 ?  Ssl  14:33   0:01 bkjs: monitor
ec2-user    899  0.0  0.6 1073844 52892 ?  Sl   14:33   0:01 bkjs: master
ec2-user    908  0.0  0.8 1081020 68780 ?  Sl   14:33   0:02 bkjs: server
ec2-user    917  0.0  0.7 1072820 59008 ?  Sl   14:33   0:01 bkjs: web
ec2-user    919  0.0  0.7 1072820 60792 ?  Sl   14:33   0:02 bkjs: web
ec2-user    921  0.0  0.7 1072120 40721 ?  Sl   14:33   0:02 bkjs: worker

To enable any task a command line parameter must be provided, it cannot be specified in the config file. The bkjs utility supports several commands that simplify running the backend in different modes.

  • bkjs start - this command is supposed to be run at the server startup as a service, it runs in the backgroud and the monitors all tasks, the env variable BKJS_SERVER can be set in the profile to one of the master or monitor to define which run mode to use, default mode is monitor
  • bkjs monitor - this command is supposed to be run at the server startup, it runs in the backgroud and the monitors all processes, the command line parameters are: -daemon -monitor -master -syslog
  • bkjs master - this command is supposed to be run at the server startup, it runs in the backgroud and the monitors all processes, the command line parameters are: -daemon -monitor -master -syslog
  • bkjs watch - runs the master and Web server in wather mode checking all source files for changes, this is the common command to be used in development, it passes the command line switches: -watch -master
  • bkjs web - this command runs just web server process.
  • bkjs run - this command runs without other parameters, all aditional parameters can be added in the command line, this command is a barebone helper to be used with any other custom settings.
  • bkjs shell or bksh - start backendjs shell, no API or Web server is initialized, only the database pools

Application structure

The main puspose of the backendjs is to provide API to access the data, the data can be stored in the database or some other way but the access to that data will be over HTTP and returned back as JSON. This is default functionality but any custom application may return data in whatever format is required.

Basically the backendjs is a Web server with ability to perform data processing using local or remote jobs which can be scheduled similar to Unix cron.

The principle behind the system is that nowadays the API services just return data which Web apps or mobiles apps can render to the user without the backend involved. It does not mean this is simple gateway between the database, in many cases it is but if special processing of the data is needed before sending it to the user, it is possible to do and backendjs provides many convenient helpers and tools for it.

When the API layer is initialized, the api module contains app object which is an Express server.

Special module/namespace app is designated to be used for application development/extension. This module is available the same way as the api or core which makes it easy to refer and extend with additional methods and structures.

The typical structure of a backendjs application is the following:

    var bkjs = require('backendjs');
    var api = bkjs.api;
    var app =;
    var db = bkjs.db;

    app.listArg = [];

    // Define the module config parameters
    core.describeArgs('app', [
        { name: "list-arg", array: 1, type: "list", descr: "List of words" },
        { name: "int-arg", type: "int", descr: "An integer parameter" },

    // Describe the tables or data models, all DB pools will use it, the master or shell
    // process only creates new tables, workers just use the existing tables

     // Optionally customize the Express environment, setup MVC routes or else, `` is the Express server
    app.configureMiddleware = function(options, callback)

    // Register API endpoints, i.e. url callbacks
    app.configureWeb = function(options, callback)
    {'/some/api/endpoint', function(req, res) {
          // to return an error, the message will be translated with internal i18n module if locales
          // are loaded and the request requires it
          api.sendReply(res, err);
          // or with custom status and message, explicitely translated
          api.sendReply(res, 404, res.__("not found"));

          // with config check
          if (app.intArg > 5) ...
          if (app.listArg.indexOf( > -1) ...

          // to send data back with optional postprocessing hooks
          api.sendJSON(req, err, data);
          // or simply

    // Optionally register post processing of the returned data from the default calls
    api.registerPostProcess('', /^\/account\/([a-z\/]+)$/, function(req, res, rows) { ... });

    // Optionally register access permissions callbacks
    api.registerAccessCheck('', /^\/test\/list$/, function(req, status, callback) { ...  });
    api.registerPreProcess('', /^\/test\/list$/, function(req, status, callback) { ...  });

Except the app.configureWeb and server.start() all other functions are optional, they are here for the sake of completness of the example. Also because running the backend involves more than just running web server many things can be setup using the configuration options like common access permissions, configuration of the cron jobs so the amount of code to be written to have fully functionaning production API server is not that much, basically only request endpoint callbacks must be provided in the application.

As with any node.js application, node modules are the way to build and extend the functionality, backendjs does not restrict how the application is structured.


Another way to add functionality to the backend is via external modules specific to the backend, these modules are loaded on startup from the backend home subdirectory modules/ and from the backendjs package directory for core modules. The format is the same as for regular node.js modules and only top level .js files are loaded on the backend startup.

By default no modules are loaded except bk_accounts|bk_icons, it must be configured by the -allow-modules config parameter.

The modules are managed per process role, by default server and master processes do not load any modules at all to keep them small and because they monitor workers the less code they have the better.

The shell process loads all modules, it is configured with .+.

To enable any module to be loaded in any process it can be configured by using a role in the config parameter:

  // Global modules except server and master
  -allow-modules '.+'

  // Master modules
  -allow-modules-master 'bk_accounts|bk_debug'

Once loaded they have the same access to the backend as the rest of the code, the only difference is that they reside in the backend home and can be shipped regardless of the npm, node modules and other env setup. These modules are exposed in the core.modules the same way as all other core submodules methods.

Let's assume the modules/ contains file facebook.js which implements custom FB logic:

     var bkjs = require("backendjs");
     var fb = {
     module.exports = fb;

     fb.configureWeb = function(options, callback) {

     fb.makeRequest = function(options, callback) {

This is the main app code:

    var bkjs = require("backendjs");
    var core = bkjs.core;

    // Using facebook module in the main app"some url", function(req, res) {

       core.modules.facebook.makeRequest({}, function(err, data) {


NPM packages as modules

In case different modules is better keep separately for maintenance or development purposes they canbe split into separate NPM packages, the structure is the same, modules must be in the modules/ folder and the package must be loadable via require as usual. In most cases just empty index.js is enough. Such modules will not be loaded via rrquire though but by the backendjs core.loadModule machinery, the NPM packages are just keep different module directories separate from each other.

The config parameter allow-packages can be used to specify NPM package names to be loaded separated by comma, as with the default application structure all subfolders inside each NPM package will be added to the core:

  • modules will be loaded from the modules/ older
  • locales from the locales/ folder
  • files in the web/ folder will be added to the static search path
  • all tempates from views/ folder will be used for rendering

If there is a config file present as etc/config it will be loaded as well, this way each package can maintain its default config parameters if necessary without touching other or global configuration. Although such config files will not be reloaded on changes, when NPM installs or updtes packages it moves files around so watching the old config is no point because the updated config file will be different.

Database schema definition

The backend support multiple databases and provides the same db layer for access. Common operations are supported and all other specific usage can be achieved by using SQL directly or other query language supported by any particular database. The database operations supported in the unified way provide simple actions like db.get, db.put, db.update, db.del, The db.query method provides generic access to the database driver and executes given query directly by the db driver, it can be SQL or other driver specific query request.

Before the tables can be queried the schema must be defined and created, the backend db layer provides simple functions to do it:

  • first the table needs to be described, this is achieved by creating a Javascript object with properties describing each column, multiple tables can be described at the same time, for example lets define album table and make sure it exists when we run our application:
           album: {
               id: { primary: 1 },                         // Primary key for an album
               name: { pub: 1 },                           // Album name, public column
               mtime: { type: "now" },                     // Modification timestamp
           photo: {
               album_id: { primary: 1 },                   // Combined primary key
               id: { primary: 1 },                         // consiting of album and photo id
               name: { pub: 1, index: 1 },                 // Photo name or description, public column with the index for faster search
               mtime: { type: "now" }
  • the system will automatically create the album and photos tables, this definition must remain in the app source code and be called on every app startup. This allows 1) to see the db schema while working with the app and 2) easily maintain it by adding new columns if necessary, all new columns will be detected and the database tables updated accordingly. And it is all Javascript, no need to learn one more language or syntax to maintain database tables.

Each database may restrict how the schema is defined and used, the db layer does not provide an artificial layer hiding all specifics, it just provides the same API and syntax, for example, DynamoDB tables must have only hash primary key or combined hash and range key, so when creating table to be used with DynamoDB, only one or two columns can be marked with primary property while for SQL databases the composite primary key can consist of more than 2 columns.

The backendjs always creates several tables in the configured database pools by default, these tables are required to support default API functionality and some are required for backend opertions. Refer below for the Javascript modules documenttion that described which tables are created by default. In the custom applications the db.describeTables method can modify columns in the default table and add more columns if needed.

For example, to make age and some other columns in the accounts table public and visible by other users with additional columns the following can be done in the api.initApplication method. It will extend the bk_account table and the application can use new columns the same way as the already existing columns. Using the birthday column we make 'age' property automatically calculated and visible in the result, this is done by the internal method api.processAccountRow which is registered as post process callback for the bk_account table. The computed property age will be returned because it is not present in the table definition and all properties not defined and configured are passed as is.

The cleanup of the public columns is done by the api.sendJSON which is used by all API routes when ready to send data back to the client. If any postprocess hooks are registered and return data itself then it is the hook responsibility to cleanup non-public columns.

        bk_account: {
            gender: { pub: 1 },
            birthday: {},
            ssn: {},
            salary: { type: "int" },
            occupation: {},
            home_phone: {},
            work_phone: {},

    app.configureWeb = function(options, callback)
       db.setProcessRow("post", "bk_account", this.processAccountRow);
    app.processAccountRow = function(req, row, options)
       if (row.birthday) row.age = Math.floor(( - core.toDate(row.birthday))/(86400000*365));

To define tables inside a module just provide a tables property in the module object, it will be picked up by database initialization automatically.

var mod = {
    name: "billing",
    tables: {
       invoices: {
          id: { type: "int", primary: 1 },
          name: {},
          price: { type: "real" },
          mtime: { type: "now" }
module.exports = mod;

// Run db setup once all the DB pools are configured, for example produce dynamic icon property
// for each record retrieved
mod.configureModule = function(options, callback)
    db.setProcessRows("post", "invoices", function(req, row, opts) {
       if ( row.icon = "/images/" + + ".png";

API requests handling

All methods will put input parameters in the req.query, GET or POST.

One way to verify input values is to use lib.toParams, only specified parameters will be returned and converted according to the type or ignored.


   var params = {
      test1: { id: { type: "text" },
               count: { type: "int" },
               email: { regexp: /^[^@]+@[^@]+$/ }
   };"/endpoint/test1", function(req, res) {
      var query = lib.toParams(req.query, params.test1);

Example of TODO application

Here is an example how to create simple TODO application using any database supported by the backend. It supports basic operations like add/update/delete a record, show all records.

Create a file named app.js with the code below.

    var bkjs = require('backendjs');
    var api = bkjs.api;
    var lib = bkjs.lib;
    var app =;
    var db = bkjs.db;

    // Describe the table to store todo records
       todo: {
           id: { type: "uuid", primary: 1 },  // Store unique task id
           due: {},                           // Due date
           name: {},                          // Short task name
           descr: {},                         // Full description
           mtime: { type: "now" }             // Last update time in ms

    // API routes
    app.configureWeb = function(options, callback)
    {^\/todo\/([a-z]+)$/, function(req, res) {
           var options = api.getOptions(req);
           switch (req.params[0]) {
             case "get":
                if (! return api.sendReply(res, 400, "id is required");
                db.get("todo", { id: }, options, function(err, rows) { api.sendJSON(req, err, rows); });
             case "select":
                options.noscan = 0; // Allow empty scan of the whole table if no query is given, disabled by default
      "todo", req.query, options, function(err, rows) { api.sendJSON(req, err, rows); });
            case "add":
                if (! return api.sendReply(res, 400, "name is required");
                // By default due date is tomorrow
                if (req.query.due) req.query.due = lib.toDate(req.query.due, + 86400000).toISOString();
                db.add("todo", req.query, options, function(err, rows) { api.sendJSON(req, err, rows); });
            case "update":
                if (! return api.sendReply(res, 400, "id is required");
                db.update("todo", req.query, options, function(err, rows) { api.sendJSON(req, err, rows); });
            case "del":
                if (! return api.sendReply(res, 400, "id is required");
                db.del("todo", { id: }, options, function(err, rows) { api.sendJSON(req, err, rows); });

Now run it with an option to allow API access without an account:

node app.js -log debug -web -api-allow-path /todo -db-create-tables

To use a different database, for example PostgresSQL(running localy) or DynamoDB(assuming EC2 instance), all config parametetrs can be stored in the etc/config as well

node app.js -log debug -web -api-allow-path /todo -db-pool dynamodb -db-dynamodb-pool default -db-create-tables
node app.js -log debug -web -api-allow-path /todo -db-pool pgsql -db-pgsql-pool default -db-create-tables

API commands can be executed in the browser or using curl:

curl 'http://localhost:8000/todo?name=TestTask1&descr=Descr1&due=2015-01-01`
curl 'http://localhost:8000/todo/select'

Backend directory structure

When the backend server starts and no -home argument passed in the command line the backend makes its home environment in the ~/.bkjs directory. It is also possible to set the default home using BKJS_HOME environment variable.

The backend directory structure is the following:

  • etc - configuration directory, all config files are there

    • etc/profile - shell script loaded by the bkjs utility to customize env variables

    • etc/config - config parameters, same as specified in the command line but without leading -, each config parameter per line:


        To specify other config file: bkjs shell -config-file file
    • etc/config.local - same as the config but for the cases when local environment is different than the production or for dev specific parameters

    • some config parameters can be condigured in DNS as TXT records, the backend on startup will try to resolve such records and use the value if not empty. All params that marked with DNS TXT can be configured in the DNS server for the domain where the backend is running, the config parameter name is concatenated with the domain and queried for the TXT record, for example: cache-host parameter will be queried for for TXT record type.

    • etc/crontab - jobs to be run with intervals, JSON file with a list of cron jobs objects:


      1. Create file in ~/.backend/etc/crontab with the following contents:

         [ { "cron": "0 1 1 * * 1,3", "job": { "app.cleanSessions": { "interval": 3600000 } } } ]
      2. Define the function that the cron will call with the options specified, callback must be called at the end, create this app.js file

         var bkjs = require("backendjs"); = function(options, callback) {
              bkjs.db.delAll("session", { mtime: options.interval + }, { ops: "le" }, callback);
      3. Start the jobs queue and the web server at once

         bkjs master -jobs-workers 1 -jobs-cron
    • etc/crontab.local - additional local crontab that is read after the main one, for local or dev environment

  • modules - loadable modules with specific functionality

  • images - all images to be served by the API server, every subfolder represent naming space with lots of subfolders for images

  • var - database files created by the server

  • tmp - temporary files

  • web - Web pages served by the static Express middleware

Cache configurations

Database layer support caching of the responses using db.getCached call, it retrieves exactly one record from the configured cache, if no record exists it will pull it from the database and on success will store it in the cache before returning to the client. When dealing with cached records, there is a special option that must be passed to all put/update/del database methods in order to clear local cache, so next time the record will be retrieved with new changes from the database and refresh the cache, that is { cached: true } can be passed in the options parameter for the db methods that may modify records with cached contents. In any case it is required to clear cache manually there is db.clearCache method for that.

Also there is a configuration option -db-caching to make any table automatically cached for all requests.


If no cache is configured the local driver is used, it keeps the cache on the master process in the LRU pool and any wroker or Web process communicate with it via internal messaging provided by the cluster module. This works only for a single server.


Set ipc-cache=memcache://HOST[:PORT] that points to the host running memcached. To support multiple servrs add the option ipc-cache-options-servers=,


Set ipc-cache=redis://HOST[:PORT] that points to the server running Redis server.

To support more than one master Redis server in the client add additional servers in the servers parameter, ipc-cache-options-servers=,, the client will reconnect automatically on every disconnect. To support quick failover it needs a parameter for the node-redis module (which is used by the driver) max_attempts to be a number how many attempts to reconnect before switching to another server like ipc-cache-options-max_attempts=3. If there is only one server then it will keep reconnecting until total reconnect time exceeds the connect_timeout ms. Any other node-redis module parameter can be passed as well.

Cache configurations also can be passed in the url, the system supports special parameters that start with bk-, it will extract them into options automatically.

For example:


Redis Sentinel

To enable Redis Sentinel pass in the option -sentinel-servers: ipc-cache=redis://host1?bk-sentinel-servers=host1,host2.

The system will connect to the sentinel, get the master cache server and connect the cache driver to it, also it will listen constantly on sentinel events and failover to a new master autimatically. Sentinel use the regular redis module and supports all the same parameters, to pass options to the sentinel driver prefix them with sentinel-:


PUB/SUB or Queue configurations

Publish/subscribe functionality allows clients to receive notifications without constantly polling for new events. A client can be anything but the backend provides some partially implemented subscription notifications for Web clients using the Long Poll. The Account API call /account/subscribe can use any pub/sub mode.

The flow of the pub/sub operations is the following:

  • a HTTP client makes /account/subscribe API request, the connection is made and is kept open indefenitely or as long as configured using api-subscribe-timeout.
  • the API backend receives this request, and runs the api.subscribe method with the key being the account id, this will subscribe to the events for the current account and registers a callback to be called if any events occured. The HTTP connection is kept open.
  • some other client makes an API call that triggers an event like makes a connectiopn or sends a message, on such event the backend API handler always runs ipc.publish after the DB operation succedes. If the messaging is configured, it publishes the message for the account, the message being a JSON object with the request API path and mtime, other properties depend on the call made.
  • the connection that initiated /account/subscribe receives an event


To configure the backend to use Redis for PUB/SUB messaging set ipc-queue=redis://HOST where HOST is IP address or hostname of the single Redis server. This will use native PUB/SUB Redis feature.

Redis Queue

To configure the backend to use Redis for job processing set ipc-queue=redisq://HOST where HOST is IP address or hostname of the single Redis server. This driver implements reliable Redis queue, with visibilityTimeout config option works similar to AWS SQS.

Once configured, then all calls to jobs.submitJob will push jobs to be executed to the Redis queue, starting somewhere a backend master process with -jobs-workers 2 will launch 2 worker processes which will start pulling jobs from the queue and execute.

An example of how to perform jobs in the API routes:

   app.processAccounts = function(options, callback) {"bk_account", { type: options.type || "user" }, function(err, rows) {

   api.all("/process/accounts", function(req, res) {
       jobs.submitJob({ job: { "app.processAccounts": { type: req.query.type } } }, function(err) {
          api.sendReply(res, err);


To configure the backend to use RabbitMQ for messaging set ipc-queue=amqp://HOST and optionally amqp-options=JSON with options to the amqp module. Additional objects from the config JSON are used for specific AMQP functions: { queueParams: {}, subscribeParams: {}, publishParams: {} }. These will be passed to the corresponding AMQP methods: amqp.queue, amqp.queue.sibcribe, amqp.publish. See AMQP node.js module for more info.


This is a simple queue implementation using the atomic UPDATE, it polls for new jobs in the table and updates the status, only who succeeds with the update takes the job and executes it. It is not effective but can be used for simple and not busy systems for more or less long jobs. The advantage is that it uses the same database and does not require additional servers.


To use AWS SQS for job processing set ipc-queue=, this queue system will poll SQS for new messeges on a worker and after succsesful execution will delete the message. For long running jobs it will automatically extend visibility timeout if it is configured.


The local queue is implemented on the master process as a list, communication is done via local sockets between the master and workers. This is intended for a single server development pusposes only.

Security configurations

API only

This is default setup of the backend when all API requests except /account/add must provide valid signature and all HTML, Javascript, CSS and image files are available to everyone. This mode assumes that Web development will be based on 'single-page' design when only data is requested from the Web server and all rendering is done using Javascript. This is how the examples/api/api.html develpers console is implemented, using JQuery-UI and Knockout.js.

To see current default config parameters run any of the following commands:

    bkjs bkhelp | grep api-allow

    node -e 'require("backendjs").core.showHelp()'

To disable open registration in this mode just add config parameter api-deny-path=^/account/add$ or if developing an application add this in the initMiddleware

    api.initMiddleware = function(callback) {
        this.allow.splice(this.allow.indexOf('^/account/add$'), 1);

Secure Web site, client verification

This is a mode when the whole Web site is secure by default, even access to the HTML files must be authenticated. In this mode the pages must defined 'Backend.session = true' during the initialization on every html page, it will enable Web sessions for the site and then no need to sign every API reauest.

The typical client Javascript verification for the html page may look like this, it will redirect to login page if needed, this assumes the default path '/public' still allowed without the signature:

   <script src="/js/jquery.js"></script>
   <link href="/css/bootstrap.css" rel="stylesheet">
   <script src="/js/bootstrap.js"></script>
   <script src="/js/knockout.js" type="text/javascript"></script>
   <script src="/js/crypto.js" type="text/javascript"></script>
   <script src="/js/bkjs.js" type="text/javascript"></script>
   <script src="/js/bkjs-bootstrap.js" type="text/javascript"></script>
   <script src="/js/bkjs-ko.js" type="text/javascript"></script>
    $(function () {
       Bkjs.session = true;
       $(Bkjs).on("nologin", function() { window.location='/public/index.html'; });

Secure Web site, backend verification

On the backend side in your application app.js it needs more secure settings defined i.e. no html except /public will be accessible and in case of error will be redirected to the login page by the server. Note, in the login page Bkjs.session must be set to true for all html pages to work after login without singing every API request.

  1. We disable all allowed paths to the html and registration:
   app.configureMiddleware = function(options, callback) {
      this.allow.splice(this.allow.indexOf('^/$'), 1);
      this.allow.splice(this.allow.indexOf('\\.html$'), 1);
      this.allow.splice(this.allow.indexOf('^/account/add$'), 1);
  1. We define an auth callback in the app and redirect to login if the reauest has no valid signature, we check all html pages, all allowed html pages from the /public will never end up in this callback because it is called after the signature check but allowed pages are served before that:
   api.registerPreProcess('', /^\/$|\.html$/, function(req, status, callback) {
      if (status.status != 200) {
          status.status = 302;
          status.url = '/public/index.html';

WebSockets connections

The simplest way is to configure ws-port to the same value as the HTTP port. This will run WebSockets server along the regular Web server. All requests must be properly signed with all parameters encoded as for GET requests.


    wscat --connect ws://localhost:8000
    connected (press CTRL+C to quit)
    > /account/get
    < {
        "status": 400,
        "message": "Invalid request: no host provided"


There is no ready to use support for different versions of API at the same because there is no just one solution that satifies all applications. But there are tools ready to use that will allow to implement such versioning system in the backend. Some examples are provided below:

  • Fixed versions This is similar to AWS version system when versions are fixed and changed not very often. For such cases the backend exposes core.bkVersion which is supposed to be a core backend version. This version is returned with every backend reponse in the Server: header. A client also can specify the core version using bk-version query parameter or a header. When a request is parsed and the version is provided it will be set in the request options object.

    All API routes are defined using Express middleware and one of the possible ways of dealing with different versions can look like this, by appending version to the command it is very simple to call only changed API code.

          api.all(/\/domain\/(get|put|del)/, function(req, res) {
              var options = api.getOptions(req);
              var cmd = req.params[0];
              if (options.appBuild) cmd += "/" + options.appBuild;
              switch (cmd) {
              case "get":

              case "get/2015-01-01":

              case "put":

              case "put/2015-02-01":

              case "del"
  • Application semver support For cases when applications support Semver kind of versioning and it may be too many releases the method above still can be used while the number of versions is small, once too many different versions with different minor/patch numbers, it is easier to support greater/less comparisons.

    The application version bk-app can be supplied in the query or as a header or in the user-agent HTTP header which is the easiest case for mobile apps. In the middlware, the code can look like this:

        var options = api.getOptions(req);
        var version = lib.toVersion(options.appVersion);
        switch (req.params[0]) {
        case "get":
            if (version < lib.toVersion("1.2.5")) {
                res.json({ id: 1, name: "name", description: "descr" });
            if (version < lib.toVersion("1.1")) {
                res.json([id, name]);
            res.json({ id: 1, name: "name", descr: "descr" });

The actual implementation can be modularized, split into functions, controllers.... there are no restrictions how to build the working backend code, the backend just provides all necessary information for the middleware modules.

The backend provisioning utility: bkjs

The purpose of the bkjs shell script is to act as a helper tool in configuring and managing the backend environment and as well to be used in operations on production systems. It is not required for the backend operations and provided as a convenience tool which is used in the backend development and can be useful for others running or testing the backend.

Running without arguments will bring help screen with description of all available commands.

The tool is multi-command utility where the first argument is the command to be executed with optional additional arguments if needed. On Linux, when started the bkjs tries to load and source the following config files:


Any of the following config files can redefine any environmnt variable thus pointing to the correct backend environment directory or customize the running environment, these should be regular shell scripts using bash syntax.

Most common used commands are:

  • bkjs watch - run the backend or the app for development purposes, uses local app.js if exists otherwise runs generic server

  • bkjs shell - start REPL shell with the backend module loaded and available for use, all submodules are available in the shell as well like core, db, api

  • bkjs sync [-path path] [-host host] [-user user] - sync sources of the app with the remote site, this is for developent version of the backend only

  • bkjs init-server [-home path] [-user user] [-host name] [-domain name] - initialize Linux instance(Amazon,CentOS) for backend use, optional -home can be specified where the backend home will be instead of ~/.bkjs, optional -user tells to use existing user instead of the current user and not root.

    This command will create /etc/sysconfig/bkjs file with BKJS_HOME set to the home of the backendjs app which was pased in the command line. This makes the bkjs or bksh run globally regardless of the current directory.

Web development notes

The server supports simple web bundling using uglify-js utility. To enable it just add tyo the local config a list of directories to be watched for changes. For example adding these lines to the local config will enable the watcher and bundle support

 build-web=bkjs web-bundle -dev

Now instead of incding a bunch of .js or css files in the html pages it only needs /js/bkjs.bundle.js and /css/bkjs.bundle.css. The configuration is in the package.json file.

The simple script below allows to build the bundle and refresh Chrome tab automatically, saves several clicks:

 bkjs web-bundle -dev -file $2
 [ "$?" != "0" ] && exit
 osascript -e "tell application \"Google Chrome\" to reload (tabs of window 1 whose URL contains \"$1\")"
 #osascript -e 'tell application "Google Chrome" to tell the active tab of its first window to reload'

To use it call this script instead in the config.local: /website

Deployment use cases

AWS instance setup with node and backendjs

Here is the example how to setup new custom AWS server, it is not required and completely optional but bkjs provies some helpful commands that may simplify new image configuration.

  • start new AWS instance via AWS console, use Amazon Linux

  • login as ec2-user

  • install commands

      yum-config-manager --enable epel
      sudo yum install npm
      npm install backendjs
      sudo bkjs init-service
      bkjs restart
  • try to access the instance via HTTP port 8000 for the API console or documentation

  • after reboot the server will be started automatically

AWS instance as an appliance

To make an API appliance by using the backendjs on the AWS instance as user ec2-user with the backend in the user home

  • start new AWS instance via AWS console, use Amazon Linux or CentOS 6

  • login as ec2-user

  • install commands

      git clone
      sudo backendjs/bkjs install-ec2 -tools $(pwd)/backendjs/tools
      bkjs restart
  • run ps agx, it should show several backend processes running

  • try to access the instance via HTTP port for the API console or documentation

NOTE: if running behind a Load balancer and actual IP address is needed set Express option in the command line -api-express-options {"trust%20proxy":1}. In the config file replacing spaces with %20 is not required.

AWS Beanstalk deployment

As with any node.js module, the backendjs app can be packaged into zip file according to AWS docs and deployed the same way as any other node.js app. Inside the app package etc/config file can be setup for any external connections.

AWS Provisioning examples

Note: on OS X laptop the -aws-sdk-profile uc when AWS credentials are in the ~/.aws/credentials.

Make an AMI

On the running machine which will be used for an image:

bksh -aws-create-image -no-reboot

Use an instance by tag for an image:

bksh -aws-create-image -no-reboot -instance-id `bkjs ec2-show -tag api -fmt id | head -1`

Launch instances when not using AutoScaling Groups

When launching from an EC2 instance no need to specify any AWS credentials.

  • admin (EC2)

    bksh -aws-sdk-profile uc -aws-launch-instances -aws-instance-type t2.small -subnet-name api -name admin -elb-name Admin -alarm-name alarms -public-ip 1 -dry-run

  • api (EC2)

    bksh -aws-sdk-profile uc -aws-launch-instances -aws-instance-type m3.large -subnet-name api -name api -elb-name api -alarm-name alarms -public-ip 1 -dry-run

  • jobs (EC2)

    bksh -aws-sdk-profile uc -aws-launch-instances -aws-instance-type t2.small -subnet-name internal -name sync -alarm-name alarms -dry-run bksh -aws-sdk-profile uc -aws-launch-instances -aws-instance-type t2.small -subnet-name internal -name sync -zone 1c -alarm-name alarms -dry-run

  • Elasticsearch

    bksh -aws-sdk-profile uc -aws-launch-instances -aws-instance-type m3.large -subnet-name internal -name elasticsearch -bkjs-cmd stop-service -bkjs-cmd "init-elasticsearch-service -memsize 50" -alarm-name alarms -public-ip 1 -dry-run

  • Redis

    bksh -aws-sdk-profile uc -aws-launch-instances -aws-instance-type m3.large -subnet-name internal -name redis -bkjs-cmd stop-service -bkjs-cmd "init-redis-service -memsize 70" -alarm-name alarms -public-ip 1 -dry-run

Launch Configurations

bksh -aws-create-launch-config -config-name elasticsearch -aws-sdk-profile uc -instance-type m3.large -update-groups -bkjs-cmd stop-service -bkjs-cmd init-logwatcher -bkjs-cmd "init-elasticsearch-service -memsize 50" -device /dev/xvda:gp2:16 -dry-run

Copy Autoscaling launch configs after new AMI is created

bksh -aws-create-launch-config -config-name jobs -aws-sdk-profile uc -update-groups -dry-run
bksh -aws-create-launch-config -config-name api -aws-sdk-profile uc -update-groups -dry-run

Update Route53 with all IPs from running instances

bksh -aws-set-route53 -name -filter elasticsearch

Proxy mode

By default the Web proceses spawned by the server are load balanced using default cluster module which relies on the OS to do scheduling. On Linux with node 0.10 this is proven not to work properly due to the kernel keeping the context switches to a minimum thus resulting in one process to be very busy while the others idle. Node versions 4 and above perform round-robin by default.

For such case the Backendjs implements the proxy mode by setting proxy-port config paremeter to any number above 1000, this will be the initial port for the web processes to listen for incoming requests, for example if use -proxy-port 3000 and launch 2 web processes they will listen on ports 3000 and 3001. The main server process will start internal HTTP proxy and will perform round-robin load balancing the incoming requests between the web proceses by forwarding them to the web processes over TCP and then returning the responses back to the clients.

Configure HTTP port

The first thing when deploying the backend into production is to change API HTTP port, by default is is 8000, but we would want port 80 so regardless how the environment is setup it is ultimatley 2 ways to specify the port for HTTP server to use:

  • config file

    The config file is always located in the etc/ folder in the backend home directory, how the home is specified depends on the system but basically it can be defined via command line arguments as -home or via environment variables when using bkjs. See bkjs documentation but on AWS instances created with bkjs init-server command, for non-standard home use /etc/sysconfig/bkjs profile, specify BKJS_HOME=/home/backend there and the rest will be taken care of

  • command line arguments

    When running node scripts which use the backend, just specify -home command line argument with the directory where yor backend should be and the backend will use it


      node app.js -home $HOME -port 80
  • config database

    If -db-config is specified in the command line or db-config= in the local config file, this will trigger loading additional config parameters from the specified database pool, it will load all records from the bk_config table on that db pool. Using the database to store configuration make it easier to maintain dynamic environment for example in case of auto scaling or lanching on demand, this way a new instance will query current config from the database and this eliminates supporting text files and distributing them to all instances.

    The config database is refreshed from time to time acording to the db-config-interval parameter, also all records with ttl property in the bk_config will be pulled every ttl interval and updated in place.

  • DNS records Some config options may be kept in the DNS TXT records and every time a instance is started it will query the local DNS for such parameters. Only a small subset of all config parameters support DNS store. To see which parmeteres can be stored in the DNS run bkjs show-help and look for 'DNS TXT configurable'.

Backend library development (Mac OS X, developers)

  • for DB drivers and ImageMagick to work propely it needs some dependencies to be installed:

      port install libpng jpeg tiff lcms2 mysql56 postgresql93
  • make sure there is no openjpeg15 installed, it will conflict with ImageMagick jp2 codec

  • git clone or git clone

  • cd backendjs

  • if node.js is already installed skip to the next section

    • to install binary release run the command, it will install it into /opt/local on Darwin

         bkjs install-node
         # To install into different path
         bkjs install-node -prefix /usr/local/node
    • Important: Add NODE_PATH=$BKJS_PREFIX/lib/node_modules to your environment in .profile or .bash_profile so node can find global modules, replace $BKJS_PREFIX with the actual path unless this variable is also set in the .profile

  • to install all dependencies and make backendjs module and bkjs globally available:

          npm link backendjs
  • to run local server on port 8000 run command:

          bkjs web
  • to start the backend in command line mode, the backend environment is prepared and initialized including all database pools. This command line access allows you to test and run all functions from all modules of the backend without running full server similar to node.js REPL functionality. All modules are accessible from the command line.

          $ ./bkjs shell
          > core.version
          > logger.setLevel('info')

Design considerations

While creating Backendjs there were many questions and issues to be considered, some i was able to implement, some still not. Below are the thoughts that might be useful when desining, developing or choosing the API platform:

  • purpose of the API:
    • to expose some parts of the existing system to external apps, users...
    • to make it the only way to access services
    • to complement another system
  • scalability considerations:
    • unlimited/uncontrolled access like mobile, web, more users the better
    • enterprise level, controlled growth
    • not to be horizontally scalable, just vertically
  • security:
    • support authentication, users, accounts, profiles...
    • just for robots, limited by api key only
    • signed requests only
    • support all access, web, mobile, desktop
    • user access controls, how to distinguish users, grant access to only parts of the API
    • ability to run custom/specific filters during processing API requests, independently and ability to extend the app without rewriting/rebuilding the whole system
    • third party authentication, OAUTH, user mapping
  • platform/framework:
    • one for all, same language/SDK/framework to cover all aspects
    • multiple languages/frameworks for different tasks, then how to integrate, how to communicate, share code
    • availability of the third party modules, libraries
    • support, forums, docs, how easy to learn for new developers
    • modularity, ability to develop by multiple developers, teams
    • flexibility in extending, how simple/easy to add custom stuff
    • maintenance, support,how easy to scale, change, replace parts
  • database layer:
    • one central database for everything
    • multiple database for different parts of the system according to scalability/other requirements
    • switch databases behind the scene in order to scale, adding to features, easier to maintain
    • caching, needs to be independent from other parts and easily enabled/disabled for different components preferably via config
    • to have or not ORM
  • process management, easy to deploy, monitor
  • logging, metrics, profiling
  • agnostic to the frontends or to be included with some kind of MVC/server based tools
  • ability to support simple Web development for simple web pages without installing/supporting general purpose tools like Apache/PHP/nginx

API endpoints provided by the backend

All API endpoints are optional and can be disabled or replaced easily. By default the naming convention is:


Any HTTP methods can be used because its the command in the URL that defines the operation. The payload can be urlencoded query parameters or JSON or any other format supported by any particular endpoint. This makes the backend universal and usable with any environment, not just a Web browser. Request signature can be passed in the query so it does not require HTTP headers at all.

Authentication and sessions


All requests to the API server must be signed with account login/secret pair.

  • The algorithm how to sign HTTP requests (Version 1, 2):
    • Split url to path and query parameters with "?"
    • Split query parameters with "&"
    • '''ignore parameters with empty names'''
    • '''Sort''' list of parameters alphabetically
    • Join sorted list of parameters with "&"
      • Make sure all + are encoded as %2B
    • Form canonical string to be signed as the following:
      • Line1: The signature version
      • Line2: The application tag or other opaque data
      • Line3: The login name
      • Line4: The HTTP method(GET), followed by a newline.
      • Line5: The host name, lowercase, followed by a newline.
      • Line6: The request URI (/), followed by a newline.
      • Line7: The sorted and joined query parameters as one string, followed by a newline.
      • Line8: The expiration value in milliseconds, required, followed by a newline
      • Line9: The Content-Type HTTP header, lowercase, optional, followed by a newline
      • Line10: The SHA1 checksum of the body content, optional, for JSON and other forms of requests not supported by query paremeters
    • Computed HMAC-SHA1 digest from the canonical string and encode it as BASE64 string, preserve trailing = if any
    • Form the signature HTTP header as the following:
      • The header string consist of multiple fields separated by pipe |
        • Field1: Signature version:
          • version 1, obsolete, do not use first 3 lines in the canonical string
          • version 2,3 to be used in session cookies only
          • version 4
        • Field2: Application tag or other app specific data
        • Field3: account login or whatever it might be in the login column
        • Field4: HMAC-SHA digest from the canonical string, version 1 uses SHA1, other SHA256
        • Field5: expiration value in milliseconds, same as in the canonical string
        • Field6: SHA1 checksum of the body content, optional, for JSON and other forms of requests not supported by query paremeters
        • Field7: empty, reserved for future use

The resulting signature is sent as HTTP header bk-signature or in the header specified by the api-signature-name config parameter.

For JSON content type, the method must be POST and no query parameters specified, instead everything should be inside the JSON object which is placed in the body of the request. For additional safety, SHA1 checksum of the JSON paylod can be calculated and passed in the signature, this is the only way to ensure the body is not modified when not using query parameters.

See web/js/bkjs.js function Bkjs.createSignature or api.js function api.createSignature for the Javascript implementations.

There is also native iOS implementation Bkjs.m.

Authentication API

  • /auth

    This API request returns the current user record from the bk_auth table if the request is verified and the signature provided is valid. If no signature or it is invalid the result will be an error with the corresponding error code and message.

    By default this endpoint is secured, i.e. requires a valid signature.


    • _session=1 - if the call is authenticated a cookie with the session signature is returned, from now on all requests with such cookie will be authenticated, the primary use for this is Web apps

    • _accesstoken=1 - returns new access token to be used for subsequent requests without a signature for the current account, the token is short lived with expiration date returned as well. This access token can be used instead of a signature and is passed in the query as bk-access-token=TOKEN.


           > { id: "XXXX...", name: "Test User", "bk-access-token": "XXXXX....", "bk-access-token-age": 604800000 }
           > { id: "XXXX...", name: "Test User", ... }
  • /login

    Same as the /auth but it uses cleartext password for user authentication, this request does not need a signature, just simple login and password query parameters to be sent to the backend.

    The intened usage is for Web sessions which use sessions cookies when sent with _session=1 or to be used with access tokens when sent with _accesstoken=1.


    • login - account login
    • password - cleartext password
    • _session=1 - same as in /auth request
    • _accesstoken=1 - same as in /auth reuest

    On successful login, the result contains full account record including the secret, this is the only time when the secret is returned back


            $.ajax({ url: "/login?login=test123&password=test123&_session=1",
                     success: function(json, status, xhr) { console.log(json) }
            > { id: "XXXX...", name: "Test User", login: "test123", ...}
  • /logout

    Logout the current user, clear session cookies if exist. For pure API access with the signature this will not do anything on the backend side.


The accounts API manages accounts and authentication, it provides basic user account features with common fields like email, name, address.

This is implemented by the accounts module from the core. To enable accounts functionality specify -allow-modules=bk_accounts.

  • /account/get

    Returns information about current account or other accounts, all account columns are returned for the current account and only public columns returned for other accounts. This ensures that no private fields ever be exposed to other API clients. This call also can used to login into the service or verifying if the given login and secret are valid, there is no special login API call because each call must be signed and all calls are stateless and independent.


    • no id is given, return only one current account record as JSON
    • id=id,id,... - return information about given account(s), the id parameter can be a single account id or list of ids separated by comma
    • _session=1 - after successful login setup a session with cookies so the Web app can perform requests without signing every request anymore
    • _accesstoken=1 - after successful login, return new access token that ca be used to make requests without signing every request, it can be passed in the query o

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