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installing_celery.md

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Install celery in an Arches project

Steps

  1. Install a celery broker, in this case we are going to use RabbitMQ.
sudo apt-get install rabbitmq-server
  1. Install Celery as a pip package. Ensure virtual environment is activated using source ENV_NAME/bin/activate
pip install celery
  1. Navigate to your project settings.py file at /my_proj/my_proj/settings.py and ensure that the following lines are set as such.
CELERY_BROKER_URL = 'amqp://guest:guest@localhost'
CELERY_RESULT_BACKEND = 'django-db'  # Use 'django-cache' if you want to use your cache as your backend

You will probably want to create a new user and password and replace ‘guest:guest’ with the new users credentials.

  1. Start RabbitMQ service
sudo service rabbitmq-server start
  1. For development, celery can be run in a terminal window using
python manage.py celery start

However, for production, we need to set up celery as a service. We will do this using Supervisord.

Running Celery as a service

  1. Install Supervisor as a pip package.
pip install supervisor

  1. In the core arches repo, in arches/install/supervisor_celery_setup there exist example files for supervisor, celeryd, and celerybeat named "my_proj_name-supervisor.conf", "my_proj_name-celeryd.conf" and "my_proj_name-celerybeat.conf", respectively.
    We are going to copy these files to resemble this structure: image

  2. Enter a separate terminal window and enter sudo su then navigate to /etc.
    Run mkdir supervisor and cd into this new directory.

  3. Copy the my_proj_name-supervisord.conf from core arches using

cp /arches/arches/install/supervisor_celery_setup/my_proj_name-supervisor.conf /etc/supervisor
  1. Make a new directory within /etc/supervisor
mkdir conf.d
  1. Copy the other two .conf files from core arches into this new directory
cp /arches/arches/install/supervisor_celery_setup/my_proj_name-celerybeat.conf /etc/supervisor/conf.d
cp /arches/arches/install/supervisor_celery_setup/my_proj_name-celeryd.conf /etc/supervisor/conf.d
  1. Rename the three files from my_proj_name to the name of your Arches project.
mv my_proj_name-supervisor.conf arches_project-supervisor.conf

  1. In each of the files make sure that:
    directory=/absolute/path/to/my_proj is changed to the path of your Arches project e.g. /home/ubuntu/arches_project
    command=/path/to/virtualenv/ is changed to the path of your virtual environment e.g. /home/ubuntu/env/ (use which python3 to find)
    user=%(ENV_USER)s is changed to the user going to run the supervisor e.g. user=ubuntu
    [app] is changed to the name of ELASTICSEARCH_PREFIX in your project’s settings.py
    And in -supervisor.conf, make sure that:
    files=./conf.d/my_proj_name-celeryd.conf is changed to the name of your arches project.

  2. Currently the formatting of the -celeryd.conf is incorrect. Ensure these two lines of your file are formatted as such:

directory=/home/ubuntu/arches_project
command=/home/ubuntu/env/bin/celery -A arches_project worker --loglevel=INFO

  1. Running supervisor now will cause errors as it cannot create the files due to current permissions. Before we can proceed, we need to change permissions of files/directories to the user entered to use supervisor.
    As root user, navigate to /var/log and mkdir supervisor
    Cd to supervisor and create the log file using touch supervisord.log and then change permissions to the user selected by chown USER supervisord.log

  2. Still as root, navigate to /var/log and mkdir celery
    Once again cd to celery and use touch worker.log and touch beat.log then chown USER worker.log and chown USER beat.log

  3. Navigate to /var/run/ and touch supervisord.pid
    Then chown USER supervisord.pid

  4. Exit as root user and return to the user you wish to run supervisor as.

  5. Run the following to start the supervisord which will start celery workers for your tasks.

supervisord -c /etc/supervisor/ARCHES_PROJECT-supervisord.conf
  1. Run the following to stop your supervisord process.
unlink /tmp/supervisor.sock
  1. To see how many celery workers are running, use ps aux | grep celery - this should usually be 1 less than the no. CPU cores.