Messages and queues disappear when trying to implement backoff logic

[wb77]

Hi, I'm implementing the backoff logic using dead-letter-exchange mechanism and x-expires queues.

And sometimes queues close unexpectedly before the end of the expired period.

I made inspection using `Event Exchange Plugin` and `Firehose` (amq.rabbitmq.event and amq.rabbitmq.trace exchanges).

I created header exchange:

    exchange: backoff

    type: headers

Then a queue with x-expires == 35000 is created and bound:

redelivered: false

    exchange: amq.rabbitmq.event

    routing_key: queue.created

    properties:

        timestamp: 1622461853 (2021-05-31T14:50:53.276000)

        delivery_mode: 2

        headers:

            user_who_performed_action: admin

            exclusive: false

            owner_pid:

            arguments: [

                <<"x-expires">>,signedint,35000

                <<"x-dead-letter-exchange">>,longstr,<<>>

            ]

            auto_delete: false

            durable: true

            name: backoff--30000ms

            vhost: /

            timestamp_in_ms: 1622461853276 (2021-05-31T14:50:53.276000)

    redelivered: false

    exchange: amq.rabbitmq.event

    routing_key: binding.created

    properties:

        timestamp: 1622461853 (2021-05-31T14:50:53.282000)

        delivery_mode: 2

        headers:

            user_who_performed_action: admin

            vhost: /

            arguments: [

                <<"backoff">>,signedint,30000

                <<"x-match">>,longstr,<<"any">>

            ]

            routing_key:

            destination_kind: queue

            destination_name: backoff--30000ms

            source_kind: exchange

            source_name: backoff

            timestamp_in_ms: 1622461853282 (2021-05-31T14:50:53.282000)

Then message with expiration of 30000 ms published in exchange:

redelivered: false

    exchange: amq.rabbitmq.trace

    routing_key: publish.backoff

    properties:

        timestamp_in_ms: 1622461853289 (2021-05-31 14:50:53.289)

        headers:

            exchange_name: backoff

            routing_keys: [

                previous_queue

            ]

            properties:

                expiration: 30000

                priority: 0

                delivery_mode: 2

                headers:

                    backoff: 30000

                content_encoding: utf-8

                content_type: application/json

            node: rabbit

            vhost: /

            connection: 127.0.0.1:59282 -> 127.0.0.1:5672

            channel: 1

            user: admin

            routed_queues: [

                backoff--30000ms

            ]

And finally after 24 seconds instead of 35 the queue was automatically deleted:

redelivered: false

exchange: amq.rabbitmq.event

routing_key: binding.deleted

properties:

    timestamp: 1622461877 (2021-05-31T14:51:17.243000)

    delivery_mode: 2

    headers:

        user_who_performed_action: rmq-internal

        vhost: /

        arguments: [

            <<"backoff">>,signedint,30000

            <<"x-match">>,longstr,<<"any">>

        ]

        routing_key: "

        destination_kind: queue

        destination_name: backoff--30000ms

        source_kind: exchange

        source_name: backoff

        timestamp_in_ms: 1622461877243 (2021-05-31T14:51:17.243000)

Queue deleted

redelivered: false

exchange: amq.rabbitmq.event

routing_key: queue.deleted

properties:

    timestamp: 1622461877 (2021-05-31T14:51:17.243000)

    delivery_mode: 2

    headers:

        user_who_performed_action: rmq-internal

        name: backoff--30000ms

        vhost: /

        timestamp_in_ms: 1622461877243 (2021-05-31T14:51:17.243000)

Documentation says "The server guarantees that the queue will be deleted, if unused for at least the expiration period" but in my case it didn't work. 

What am I doing wrong?

RabbitMQ 3.8.0

Erlang 22.1.2