Methods to determine deprecated features in use report incomplete/inaccurate information

[Zerpet]

Describe the bug

The command rabbitmq-diagnostics check_if_any_deprecated_features_are_used and the API endpoint /api/deprecated-features/used do not report accurate information on actual state of the system. The command/endpoint only seem to check for classic queue mirroring, and it doesn't report the state of other deprecated features in use.

Reproduction steps

1. Start RabbitMQ 4.0.3 (latest at this time): docker run --name bunny -p 15672:15672 --rm rabbitmq:4.0-management
2. List deprecated features: docker exec bunny rabbitmq-diagnostics --formatter=pretty_table list_deprecated_features
   Observe transient_nonexcl_queues as deprecated feature, permitted by default
3. Create a transient non-exclusive classic queue:

   curl -v -u guest:guest -H "Content-Type: application/json" -d '{"auto_delete":false,"durable":false}' -X PUT http://localhost:15672/api/queues/%2F/myqueue
   

4. Query the state of deprecated features used: curl -v -u guest:guest http://localhost:15672/api/deprecated-features/used
5. Observe that none [] are reported
6. Observe that server logs print Deprecated features: transient_nonexcl_queues: Feature transient_nonexcl_queues is deprecated.
7. Run docker exec bunny rabbitmq-diagnostics --formatter=pretty_table check_if_any_deprecated_features_are_used
8. Observe the reported output: Cluster reported no deprecated features in use

Expected behavior

The command rabbitmq-diagnostics --formatter=pretty_table check_if_any_deprecated_features_are_used reports that transient_nonexcl_queues deprecated feature is used.

The API endpoint /api/deprecated-features/used reports that transient_nonexcl_queues deprecated feature is used.

Additional context

Setting deprecated_features.permit.transient_nonexcl_queues = false causes the queue declare operation to fail right away.

[michaelklishin]

It's the CLI command that specifically only checks for CMQs.

[Zerpet]

It's the CLI command that specifically only checks for CMQs.

Strange, I can reproduce the issue using the HTTP API as well 😕

[michaelklishin]

Maybe the HTTP API endpoints do the same thing, the CLI command was the first thing I've taken a look at.

[dumbbell]

In the specific case of transient_nonexcl_queues, the deprecated feature doesn’t define a is_feature_used() callback. Therefore the subsystem can’t tell if it is used or not.

This is the first thing to add if we want something accurate. I will prepare a patch.

[dumbbell]

Adding a is_feature_used callback to transient_nonexcl_queues is enough to have it listed in the API enpoint:

[
  {
    "name": "transient_nonexcl_queues",
    "desc": "",
    "deprecation_phase": "permitted_by_default",
    "doc_url": "https://blog.rabbitmq.com/posts/2021/08/4.0-deprecation-announcements/#removal-of-transient-non-exclusive-queues",
    "provided_by": "rabbit"
  }
]

It is not enough for the CLI command though, so it must not call the deprecated feature subsystem correctly.

Edit: Indeed, as Michael, the CLI is not calling the subsystem at all. It does its own thing specifically for classic mirrored queues.

[dumbbell]

Both pull requests are ready for review! @Zerpet: could you please give them a try? You will need both to fix the problem entirely.