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Our lists of rabbitmq queues was likely to end up out of date, since there was nothing enforcing that the various lists of queues were correct or the same as each other.
85 lines
3.1 KiB
Markdown
85 lines
3.1 KiB
Markdown
# Queue processors
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Zulip uses RabbitMQ to manage a system of internal queues. These are
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used for a variety of purposes:
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* Asynchronously doing expensive operations like sending email
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notifications which can take seconds per email and thus would
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otherwise timeout when 100s are triggered at once (E.g. inviting a
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lot of new users to a realm).
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* Asynchronously doing non-time-critical somewhat expensive operations
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like updating analytics tables (e.g. UserActivityInternal) which
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don't have any immediate runtime effect.
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* Communicating events to push to clients (browsers, etc.) from the
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main Zulip Django application process to the Tornado-based events
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system. Example events might be that a new message was sent, a user
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has changed their subscriptions, etc.
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* Processing mobile push notifications and email mirroring system
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messages.
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* Processing various errors, frontend tracebacks, and slow database
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queries in a batched fashion.
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* Doing markdown rendering for messages delivered to the Tornado via
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websockets.
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Needless to say, the RabbitMQ-based queuing system is an important
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part of the overall Zulip architecture, since it's in critical code
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paths for everything from signing up for account, to rendering
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messages, to delivering updates to clients.
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We use the `pika` library to interface with RabbitMQ, using a simple
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custom integration defined in `zerver/lib/queue.py`.
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### Adding a new queue processor
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To add a new queue processor:
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* Define the processor in `zerver/worker/queue_processors.py` using
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the `@assign_queue` decorator; it's pretty easy to get the template
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for an existing similar queue processor. This suffices to test your
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queue worker in the Zulip development environment
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(`tools/run-dev.py` will automatically restart the queue processors
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and start running your new queue processor code). You can also run
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a single queue processor manually using e.g. `./manage.py
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process_queue --queue=user_activity`.
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* So that supervisord will known to run the queue processor in
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production, you will need to add to to `normal_queues` in
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`puppet/zulip/manifests/base.pp`; the list there is used to generate
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`/etc/supervisor/conf.d/zulip.conf` via a puppet template in
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`app_frontend.pp`.
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The queue will automatically be added to the list of queues tracked by
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`scripts/nagios/check-rabbitmq-consumers`, so Nagios can properly
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check whether a queue processor is running for your queue. You still
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need to update the sample Nagios configuration in `puppet/zulip_ops`
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manually.
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### Publishing events into a queue
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You can publish events to a RabbitMQ queue using the
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`queue_json_publish` function defined in `zerver/lib/queue.py`.
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### Clearing a RabbitMQ queue
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If you need to clear a queue (delete all the events in it), run
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`./manage.py purge_queue <queue_name>`, for example:
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```
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./manage.py purge_queue user_activity
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```
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You can also use the amqp tools directly. Install `amqp-tools` from
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apt and then run:
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```
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amqp-delete-queue --username=zulip --password='...' --server=localhost \
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--queue=user_presence
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```
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with the RabbitMQ password from `/etc/zulip/zulip-secrets.conf`.
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