Zulip uses RabbitMQ to manage a system of internal queues. These are used for a variety of purposes:
- Asynchronously doing expensive operations like sending email notifications which can take seconds per email and thus would otherwise timeout when 100s are triggered at once (E.g. inviting a lot of new users to a realm).
- Asynchronously doing non-time-critical somewhat expensive operations like updating analytics tables (e.g. UserActivityInternal) which don’t have any immediate runtime effect.
- Communicating events to push to clients (browsers, etc.) from the main Zulip Django application process to the Tornado-based events system. Example events might be that a new message was sent, a user has changed their subscriptions, etc.
- Processing mobile push notifications and email mirroring system messages.
- Processing various errors, frontend tracebacks, and slow database queries in a batched fashion.
- Doing markdown rendering for messages delivered to the Tornado via websockets.
Needless to say, the RabbitMQ-based queuing system is an important part of the overall Zulip architecture, since it’s in critical code paths for everything from signing up for account, to rendering messages, to delivering updates to clients.
We use the
pika library to interface with RabbitMQ, using a simple
custom integration defined in
Adding a new queue processor¶
To add a new queue processor:
- Define the processor in
@assign_queuedecorator; it’s pretty easy to get the template for an existing similar queue processor. This suffices to test your queue worker in the Zulip development environment (
tools/run-dev.pywill automatically restart the queue processors and start running your new queue processor code). You can also run a single queue processor manually using e.g.
./manage.py process_queue --queue=user_activity.
- So that supervisord will known to run the queue processor in
production, you will need to add to to
puppet/zulip/manifests/base.pp; the list there is used to generate
/etc/supervisor/conf.d/zulip.confvia a puppet template in
The queue will automatically be added to the list of queues tracked by
scripts/nagios/check-rabbitmq-consumers, so Nagios can properly
check whether a queue processor is running for your queue. You still
need to update the sample Nagios configuration in
Publishing events into a queue¶
You can publish events to a RabbitMQ queue using the
queue_json_publish function defined in
An interesting challenge with queue processors is what should happen
when queued events in Zulip’s backend tests. Our current solution is
that in the tests,
queue_json_publish will (by default) simple call
consume method for the relevant queue processor. However,
queue_json_publish also supports being passed a function that should
be called in the tests instead of the queue processor’s
method. Where possible, we prefer the model of calling
tests since that’s more predictable and automatically covers the queue
processor’s code path, but it isn’t always possible.
Clearing a RabbitMQ queue¶
If you need to clear a queue (delete all the events in it), run
./manage.py purge_queue <queue_name>, for example:
./manage.py purge_queue user_activity
You can also use the amqp tools directly. Install
apt and then run:
amqp-delete-queue --username=zulip --password='...' --server=localhost \ --queue=user_presence
with the RabbitMQ password from