rabbitmq_queue_exchange_messages_published_total in /metrics/per-object has a duplicate vhost label

[Gama11]

Describe the bug

Prometheus seems to choke on duplicate labels:

Note how vhost appears twice here:

# TYPE rabbitmq_queue_exchange_messages_published_total counter
# HELP rabbitmq_queue_exchange_messages_published_total Total number of messages published into a queue through an exchange
rabbitmq_queue_exchange_messages_published_total{vhost="/",queue="<queue-name>",vhost="/",exchange="<exchange-name>"} 19

Versions used:

• rabbitmq:4.0.0-management-alpine
• prom/prometheus:v2.54.1

This seems to be a regression compared to 3.13.7 which we upgraded from.

Reproduction steps

1. Enable the rabbitmq_prometheus plugin
2. Send some messages to a queue so the rabbitmq_queue_exchange_messages_published_total metric is included
3. Query the /metrics/per-object endpoint

Expected behavior

There should not be duplicate labels.

Additional context

No response

[Gama11]

Possibly relevant, our rabbitmq.config:

[
  {
    rabbit,
      [
        { loopback_users, [] }
      ]
  },
  {
    rabbitmq_management,
      [
        { load_definitions, "/etc/rabbitmq/definitions.json" }
      ]
  }
].

definitions.json:

{
  "users": [
    {
      "name": "test",
      "password_hash": "<redacted>",
      "hashing_algorithm": "rabbit_password_hashing_sha256",
      "tags": "administrator,monitoring"
    }
  ],
  "vhosts": [
    {
      "name": "/"
    }
  ],
  "permissions": [
    {
      "user": "test",
      "vhost": "/",
      "configure": ".*",
      "write": ".*",
      "read": ".*"
    }
  ],
  "topic_permissions": [],
  "parameters": [],
  "global_parameters": [],
  "policies": [],
  "queues": [],
  "exchanges": [],
  "bindings": []
}

[michaelklishin]

Thank you. This looks like a blank node's config with a pre-configured user for remote access.

I was able to reproduce with a blank node from main:

# HELP rabbitmq_queue_exchange_messages_published_total Total number of messages published into a queue through an exchange
rabbitmq_queue_exchange_messages_published_total{vhost="/",queue="qq.1",vhost="/",exchange=""} 100000

[gomoripeti]

I think this is related to #11559
the first vhost belongs to the queue, the second to the exchange but obviously they are the same so need to special handle this new case to eliminate the redundancy

[Gama11]

I noticed that rabbitmq_queue_messages_published_total has two labels called exchange_vhost and queue_vhost (or at least it did in 3.13.7).

[pschichtel]

is there ever a case where a queue's vhost and the exchange's vhost would be different?

[michaelklishin]

@pschichtel no, by definition, entities in different virtual hosts cannot be bound together.

[michaelklishin]

The labels may simply reflect the fact that there are two associated entities with certain metric samples, and they both belong to a virtual host. Ideally it should be just vhost, virtual_host, or whatever is the label we use for other metrics.

[michaelklishin]

A fix was contributed by @LoisSotoLopez in #12364, merged in #12373 and (will be) backported in #12378.