servicectl
Servicectl is a opinionated process manager that aim to simplify native init systems for developers.
Last updated 3 months ago by vmarchaud .
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Servicectl

Servicectl is a optionated process manager that aim to simplify native init systems for developers.

Currently it only support linux distribution with systemd, if you really need it to support windows or macos please open an issue.

Getting started

# Install the CLI first
npm install -g servicectl
# or
yarn global add servicectl

# start your app
sudo servicectl create myapp.js --name myapp
# or with the cluster mode (see under for explaination) 
sudo servicectl create myapp.js --instances 2 --port 8080

# get your logs
servicectl logs myapp --lines 100

# restart your app
sudo servicectl restart myapp

# see the status of your app
servicectl status

# remove the application from your system
sudo servicectl delete myapp

Why Yet Another Process Manager?

I believe most process manager implementations focus on delivering a good experience for developers by re-implementing a daemon and a CLI from scratch (ex: pm2, forever, nodemon, supervisor).

While it help for developers to run their apps, they generally are reinventing the wheel because popular OS already have a process manager builtin: systemd for most linux distributions, launchd for macOS and Service Control Manager for Windows.

In theory it should not be a problem but in practive you will often find bugs that doesn't exist in native init systems because they are generally older, well tested and handle a larger scope of use-case.

Anoter argument would be that using the native init system cost less in terms of resources, embed environment like raspberry-pi like system are an example where it could help a lot.

Why not use the native init system of my OS then?

You are right, in a perfect world this tool would be almost useless because everyone would be leveraging their already-present init systems. However the existence of simpler process manager means (in my opinion at least) that some people find them too difficult to use or configure.

Servicectl aim to help those people, people who aren't system administrator but still need to deploy their applications in production. However it can also help sysadmin since you can use native CLI (systemctl on linux for exemple) after starting the app with servicectl.

If I use containers I don't see the point of using your tool!

That's because there are no point (expect some rare cases (ex: coreos)) of using init systems if you use containers. You should have a scheduler like kubernetes, nomad or rancher (etc.) to manage them. I have no plans to allow to manage them via servicectl.

What servicectl is not:

  • A development process manager: I don't plan to support a watch mode for example or any feature that is not used in production.
  • A way to manage containers: as said above, you should be using more mature tools to do that.

Features

Start an application

To start an application, you need to use servicectl create which will register it to your init system:

# note that you must use sudo on linux
sudo servicectl create app.js

The configuration is immutable which means that to update it, you will need to delete the app and re-create it. To see all the flag that you can use, use servicectl create -h. By default the app will be launched in exec mode, which means it will only exist one instance of your app. If you want to launch different instances, use the cluster mode.

Environment variables

The advised way to pass them is to have a .env file on your filesystem and to give it as argument with the flag --env-file <path>. You can also use -e KEY=VALUE or --env KEY=VALUE but again, a env file is generally better. If you want to import your current shell environment into the application use --import-env.

Permissions

By default the application will run with the same user as the one you are using to interact with the CLI, but can modify it using --as=value:

  • --as=user: default behavior, use the current user.
  • --as=nobody: best options, it will create a temporary user/group that got almost no permissions.
  • --as=root: really really not advised (please only use it if you know what you are doing) run the application as root.

Get a list of applications running

Different aliases are available (ls, ps, status) will give you this ouput:

servicectl ps

Name   State  Mode    Uptime     CPU (%) Memory (MB) 
http@1 active cluster 7 sec. ago 0       7.66        
http@0 active cluster 8 sec. ago 0       7.63 

You also have different flag to sort, filter and format the list, please refer to servicectl ps -h. The name also contains the number of the instance for a given app (in the format <name>@<number>) if you are using the cluster mode.

Cluster mode

If you used PM2 before, there is a mode called cluster which allows to automatically load balance requests to multiple instances of your app. You can do that with servicectl too:

# you need to specify the port that the application listen on
# otherwise it will not work.
servicectl create app.js --instances 2 --port 3000

Like PM2, the cluster mode is supported out of the box using Node.js. However you can use it anything, please read how to setup socket-enabled systemd service with your language (it's easy as listening on a specific file descriptor):

After changing your code to use the custom file descriptor, just launch your app like above and it should works.

Note that if you are using the cluster mode, you can bind to port under 1000 (without having your app running as root).

Logs

Log of each service are stored inside /var/log/servicectl/ for linux, you can retrieve them using:


# fetch the 15th last lines
servicectl logs <name>

# follow new log
servicectl logs <name> -f

# get n last lines
servicectl logs <name> -n count

Restart

You can restart one or multiple applications like this:

servicectl restart <name> | all

Delete

As said in the Create section, you need to delete your application to update its config, to do that you can use:

# note that you need to use sudo on linux
sudo servicectl delete <name> | all

API

servicectl defines a common service definition as well as common init system API (here) and implements them for each backend (here). You could totally use it as an API, I would advise to check how the CLI commands are interacting with it here

Note that the initial version of servicectl only includes support for systemd, if you need to use it on another init system please open an issue if your use-case.

Versioning

This library follows Semantic Versioning.

Before the 1.0.0 release, any minor update can have breaking changes.

LICENSE

Apache License 2.0

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