POC of using Supervisor inside docker container

About Supervisor

Features:

manages pool of apps defined in configuration file
can work as foreground process, not daemon - required for Docker container
can automatically restart app depending on its configuration
can detect if application stopped immediately (even with code 0), mainly due of startup error - allows to define minimum working time of application to be considered as RUNNING.
handles signals properly - terminates all processes by SIGTERM (it seems to be configurable), and listens for signal itself - allow to gracefully terminate processes
has XML-RPC interface and provides Python client library to interact with it
allows to define event listener, able to react on specific events
seems to have good community with many plugins

Usage

Starting:

$ docker-compose up

Logs:

$ docker-compose logs -f supervisord-demo

Stopping container (gracefully):

$ docker-compose down

Force shutdown single app with REST API (should gracefully shutdown whole container):

curl --request POST "http://localhost:8080/stop" \
     --header 'Content-Type: application/json' \
     -d '{ "exitCode": 1, "delay": 2000 }'

Or using provided script:

./demo/stop.sh 8080 1 2000

(arguments: port exitCode delay)

Force log some text to console

curl --request POST "http://localhost:8080/log/{level}" \
     --header 'Content-Type: text/plain' \
     -d 'message'

where level is one of following: error, warn, info, debug, trace.

Using provided script:

./demo/log.sh 8080 'message' info

(arguments: port message level)

supervisord.conf

Configuration file for Supervisor (documentation). Defines:

inet_http_server with XML-RPC interface to control Supervisor. Works on 127.0.0.1:9001 with credentials test:test.
Two supervised apps (see below)
Event listener (see below)
Logs from Supervisord and event listener are written in /var/log/supervisor directory (it must be created manually when running outside of docker).

python_tools/shutdown_listener.py

Example event listener, terminates whole Supervisor tree when one of processes closes itself.

node_apps

Two simple Node.JS apps which are supervised. Both have simple REST API, running on ports 8080 and 8081. These apps also listen for SIGINT/SIGTERM and finishes with small delay to emulate shutdown logic.

Ping

GET /ping

Returns always 200 OK with body OK - may be used as health check.

Stop

POST /stop

{
  "exitCode": 1,
  "delay": 1000
}

Schedules stopping with exitCode in delay ms. Both exitCode and delay are optional. Default:

{
  "exitCode": 0,
  "delay": 10
}

Logs

POST /logs/{level}
Content-Type: text/plain

{message}

Logs given message to STDOUT with level, where level is one of: error, warn, info, debug, trace.

rafw87 / supervisord-docker-poc