Supervisor as a Background Service Manager

Supervisor, often called supervisord, is a simple way to manage processes that you need your pi to run. In our case, we’re using it to run a minimal python web application (flask).

1. Install

sudo apt install supervisor -y

2. Start Supervisor

sudo service supervisor start

3. Create a Supervisor Process

Be sure to enable the correct permissions on the user or the user’s group so the below process can actually run.

All of your custom processes will live in the following directory:

/etc/supervisor/conf.d/

Create file project.supervisor.conf and put:

[program:flaskapp]
user=pi
directory=/home/pi/app
command=/home/pi/app/bin/gunicorn wsgi:app
 
autostart=true
autorestart=true
stdout_logfile=/var/log/www/flaskapp/stdout.log
stderr_logfile=/var/log/www/flaskapp/stderr.log

• [program:<appname>] The <appname> setting here is the name of the supervisor process so we can run various commands (see step 4). Again, flaskapp is the <appname>

• user is the user you want this process to run as. We’ll stick with our default pi user.

• directory: Default working directory

• command: What command do we need this process to run? In my case, I’m using a Python virtual environment (ie /home/pi/app/bin/) with gunicorn installed. This command can be any valid bash shell command. For more on gunicorn & supervisor go here.

• autostart: start on system boot (true / false)
• autorestart Restart on failure (true / false)
• stdout_logfile stdout log file location
• stderr_logfile stderr log file location

4. Update Supervisor

sudo supervisorctl reread
sudo supervisorctl update

These two commands will let supervisor know of our new process (reread) and it will run it (update).

5. Verify Commands

sudo supervisorctl status flaskapp
sudo supervisorctl start flaskapp
sudo supervisorctl stop flaskapp
sudo supervisorctl restart flaskapp

6. Check logs

In our project.supervisor.conf from Step 3, we have the following log paths:

/var/log/www/flaskapp/stdout.log

and

/var/log/www/flaskapp/stderr.log

These logs are useful to uncover errors with your application running.