Coding for Entrepreneurs

Hello Linux: Celery & Supervisor

By Justin

Hello Linux: Celery & Supervisor
This is the eight post of a many part series. This post is the starter post for the whole series.
Celery is a Python package that integrates with Redis (or RabbitMQ) to help offload various functions from your core python app. This is very useful for things like generating repots, processing data, and even scheduling periodic tasks.
Supervisor is a process manager (as you likely know) that will ensure that Celery is running along side of your app.
Requirements
Be sure to complete
Our Live Server
  • Ubuntu 18.04

1. Celery + Redis + Django

We've covered this in detail before in this guide in this Guide. Naturally ignore the heroku portion if you intend to do the rest of this guide.

2. SSH into your server

ssh [email protected]
Replace [email protected] with your user / ip

3. Install & Start Supervisor

Assuming you did this post recently, you shouldn't need to do this.
sudo apt-get update -y

sudo apt-get install supervisor -y 

sudo service supervisor start

4. Install Celery in our Working Directory's Virtualenv

Find the Virtualenv bin that you created in this post
Mine is /var/www/myproject/bin/
/var/www/myproject/bin/python -m pip install "celery[redis]" redis
Fun note; if you already installed redis/celery locally, updated requirements.txt, did a push, there's a good chance your celery is already installed.

5. Verify Celery works

/var/www/hello_linux/bin/celery -A
You should see
usage: celery [-h] [-A APP] [-b BROKER] [--result-backend RESULT_BACKEND]
              [--loader LOADER] [--config CONFIG] [--workdir WORKDIR]
              [--no-color] [--quiet]
celery: error: argument -A/--app: expected one argument
You should not see:
-bash: /var/www/myproject/bin/celery: No such file or directory

6. Create a Supervisor Process

Almost the same exact instructions from here With supervisor, we can run step 4 automatically, restart it if it fails, create logs for it, and start/stop it easily.
Basically, this ensures that our web server will continue to run if you push new code, server reboots/restarts/goes down and back up, etc.
Of course, if a catastrophic error occurs (or if bad code is in your Django project) then this proceess might fail as well.
All supervisor proccesses go in:
/etc/supervisor/conf.d/
So, if you ever need to add a new process, you'll just add it there.
Let's create our project's celery configuration file for supervisor.
touch /etc/supervisor/conf.d/myproject-celery.conf
Now you should see:
$ ls -al /etc/supervisor/conf.d/
myproject-celery.conf
Now, let's add the base settings:
[program:myproject_celery]
user=root
directory=/var/www/myproject/src/
command=/var/www/myproject/bin/celery -A myproject worker -l info
 
autostart=true
autorestart=true
stdout_logfile=/var/log/myproject/celery.log
stderr_logfile=/var/log/myproject/celery.err.log"
Let's break it down line by line.
[program:myproject_celery]
: the myproject_celery is the name of the supervisor process. Naturally, myproject_celery is an arbitrary name. Once we complete Step 5, you'll be able to run the following commands:
  • sudo supervisorctl status myproject_celery
  • sudo supervisorctl start myproject_celery
  • sudo supervisorctl stop myproject_celery
  • sudo supervisorctl restart myproject_celery
user=root
: Set the user you want to allow access to this process. This must be set.
directory=/var/www/myproject/src/
This is the working directory for your project (notice mine has src at the end)
command=...
This is the command you want your process to run. Our command is: - /var/www/myproject/bin/celery This is the recently installed celery bash command - -A myproject This is a celery argument for where your project's celery app is located. Mine is in celery.py in my main Django conf directory. (We'll add this in the next step). In my case it's src directory -> cfehome module -> celery module -> celery application - -l info This just means "log level is info" so we just get general info about this app. Check the celery docs for more log levels.
autostart
Do you want this process to auto start? We do.
autorestart
Do you want this process to auto restart if things fail? We do.
stdout_logfile
and stderr_logfile are locations for log files. You might need to run mkdir /var/log/myproject/ to ensure these files are actually added. These log files are great for diagnosing errors.

7. Update Supervisor

supervisorctl reread
supervisorctl update

8. Check Our Supervisor Program/Process Status

As we mentioned when we crated the myproject_guincorn supervisor program, we can now do:
sudo supervisorctl status myproject_celery
A few other useful commands (again):
  • sudo supervisorctl start myproject_celery
  • sudo supervisorctl stop myproject_celery
  • sudo supervisorctl restart myproject_celery

Wrap Up

We now have
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Hello Linux: Celery & Supervisor