rhubarb 0.2.0

Avoid running multiple instances of the same celery task concurrently

Lock-based celery tasks using Redis

rhubarb provides a LockableTask which implements the Redlock algorithm in order to guarantee that only one instance of a given task is running at the same time, while preventing deadlocks from happening in case of e.g. a worker getting killed, which is not uncommon in cloud environments.

Why use rhubarb?

There are certainly other very similar libraries and tools that can help you achieve the same results, but rhubarb aims to be a very opinionated approach to the same problem these other libraries solve. You can use rhubarb without changing any settings and be confident that the defaults will be enough to not worry about it.

Rhubarb's long-term goal is to guarantee exclusive task execution with minimal, almost inexistent downtime while taking resiliency towards unexpected worker termination very seriously.

Usage

from rhubarb.tasks import LockableTask

@app.task(base=LockableTask)
def my_task():
    ...

Settings

See the official celery docs on where/how to set the following settings:

• rhubarb_backend_url: URL to the Redis instance which will be used for creating the locks. If not present, will fallback to Celery's broker_url or result_backend settings, in that order of precedence.
• rhubarb_backend_kwargs: Dict of keyword arguments to pass to the Redis connection constructor, use for anything not present in the URL. Note that query parameters in the URL always take precedence over key-value pairs in this dict.
• rhubarb_task_lock_ttl: Global default expiry time for locks in seconds, if not present will default to 60 minutes.

Testing

• Make sure you install both requirements.txt and requirements-testing.txt.
• Set up a local Redis instance, the tests/ directory includes a compose.yml file which sets up a local Redis instance using docker and docker-compose.
• Run the tox command.

Why is it called rhubarb?

It's a plugin for celery that implements the Redlock algorithm using Redis... Have you ever seen a rhubarb? It's practically a red celery :-)