Celery RabbitMQ Quorum queues with a list of `broker

The Fix

pip install celery==5.5.1

Based on closed celery/celery issue #9651 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -38,3 +38,4 @@ integration-tests-config.json
 dump.rdb
 .env
+junit.xml
diff --git a/celery/worker/consumer/delayed_delivery.py b/celery/worker/consumer/delayed_delivery.py
index d7cacd08068..7a39c60f090 100644

repro.py

CELERY_ACCEPT_CONTENT: ['application/json']
CELERY_BROKER_URL: 'amqp://breww-rabbitmq:********@rabbitmq:5672//'
CELERY_CACHE_BACKEND: 'django-cache'
CELERY_RESULT_SERIALIZER: 'json'
CELERY_TASK_ACKS_LATE: True
CELERY_TASK_DEFAULT_PRIORITY: 5
CELERY_TASK_REJECT_ON_WORKER_LOST: True
CELERY_TASK_SERIALIZER: 'json'
CELERY_TIMEZONE: 'UTC'
CELERY_WORKER_PREFETCH_MULTIPLIER: 2

is_overridden: <bound method Settings.is_overridden of <Settings "goBrew.settings">>
deprecated_settings: None
task_default_queue: 'cq_normal'
task_default_queue_type: 'quorum'
task_queues: [<unbound Queue cq_urgent -> <unbound Exchange ''(direct)> -> >,
 <unbound Queue cq_elasticsearch -> <unbound Exchange ''(direct)> -> >]
broker_transport_options:
    'confirm_publish': True,
    'health_check_interval': 5,
    'queue_order_strategy': 'priority',
    'redis_retry_on_timeout': True,
    'retry_on_error': True,
    'socket_keepalive': True}
broker_connection_retry_on_startup: True
broker_connection_retry: True
broker_channel_error_retry: True

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install celery==5.5.1\nWhen NOT to use: This fix should not be applied if the broker URLs are guaranteed to be strings.\n\n

Why This Fix Works in Production

Trigger: [2025-04-02 10:00:04,411: INFO/MainProcess] Connected to amqp://breww-rabbitmq:**@rabbitmq:5672//
Mechanism: The code attempted to call 'strip' on a list instead of a string
Why the fix works: Fixed an AttributeError when using a list of broker URLs with quorum queues. (first fixed release: 5.5.1).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Shows up under Python 3.13 in real deployments (not just unit tests).
The code attempted to call 'strip' on a list instead of a string
Surfaces as: [2025-04-02 10:00:04,411: INFO/MainProcess] Connected to amqp://breww-rabbitmq:**@rabbitmq:5672//

Proof / Evidence

GitHub issue: #9651
Fix PR: https://github.com/celery/celery/pull/9657
First fixed release: 5.5.1
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.27

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Thank you for fixing so promptly :pray: And all the work that has gone into 5.5.0 :boom:”

@violuke · 2025-04-04 · source

“> Thank you for fixing so promptly 🙏 And all the work that has gone into 5.5.0 💥 Thank you for reporting! This is a…”

@Nusnus · 2025-04-04 · source

“@violuke if you want you can give main a shot and report here, or open a new ticket if you see anything else, and I’ll…”

@Nusnus · 2025-04-04 · source

“Thank you. I can confirm this seems to be working. Just deployed to production so will follow up if anything else comes to light :+1:”

@violuke · 2025-04-08 · source

Failure Signature (Search String)

[2025-04-02 10:00:04,411: INFO/MainProcess] Connected to amqp://breww-rabbitmq:**@rabbitmq:5672//

Error Message

Stack trace

error.txt

Error Message
-------------
[2025-04-02 10:00:04,411: INFO/MainProcess] Connected to amqp://breww-rabbitmq:**@rabbitmq:5672//
[2025-04-02 10:00:04,415: INFO/MainProcess] mingle: searching for neighbors
[2025-04-02 10:00:05,440: INFO/MainProcess] mingle: all alone
[2025-04-02 10:00:05,456: INFO/MainProcess] Global QoS is disabled. Prefetch count in now static.
[2025-04-02 10:00:05,461: CRITICAL/MainProcess] Unrecoverable error: AttributeError("'list' object has no attribute 'strip'")
Traceback (most recent call last):
  File "/app/.venv/lib/python3.13/site-packages/celery/worker/worker.py", line 203, in start
    self.blueprint.start(self)
    ~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/app/.venv/lib/python3.13/site-packages/celery/bootsteps.py", line 116, in start
    step.start(parent)
    ~~~~~~~~~~^^^^^^^^
  File "/app/.venv/lib/python3.13/site-packages/celery/bootsteps.py", line 365, in start
    return self.obj.start()
           ~~~~~~~~~~~~~~^^
  File "/app/.venv/lib/python3.13/site-packages/celery/worker/consumer/consumer.py", line 341, in start
    blueprint.start(self)
    ~~~~~~~~~~~~~~~^^^^^^
  File "/app/.venv/lib/python3.13/site-packages/celery/bootsteps.py", line 116, in start
    step.start(parent)
    ~~~~~~~~~~^^^^^^^^
  File "/app/.venv/lib/python3.13/site-packages/celery/worker/consumer/delayed_delivery.py", line 74, in start
    self._validate_configuration(app)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
... (truncated) ...

Minimal Reproduction

repro.py

CELERY_ACCEPT_CONTENT: ['application/json']
CELERY_BROKER_URL: 'amqp://breww-rabbitmq:********@rabbitmq:5672//'
CELERY_CACHE_BACKEND: 'django-cache'
CELERY_RESULT_SERIALIZER: 'json'
CELERY_TASK_ACKS_LATE: True
CELERY_TASK_DEFAULT_PRIORITY: 5
CELERY_TASK_REJECT_ON_WORKER_LOST: True
CELERY_TASK_SERIALIZER: 'json'
CELERY_TIMEZONE: 'UTC'
CELERY_WORKER_PREFETCH_MULTIPLIER: 2

is_overridden: <bound method Settings.is_overridden of <Settings "goBrew.settings">>
deprecated_settings: None
task_default_queue: 'cq_normal'
task_default_queue_type: 'quorum'
task_queues: [<unbound Queue cq_urgent -> <unbound Exchange ''(direct)> -> >,
 <unbound Queue cq_elasticsearch -> <unbound Exchange ''(direct)> -> >]
broker_transport_options:
    'confirm_publish': True,
    'health_check_interval': 5,
    'queue_order_strategy': 'priority',
    'redis_retry_on_timeout': True,
    'retry_on_error': True,
    'socket_keepalive': True}
broker_connection_retry_on_startup: True
broker_connection_retry: True
broker_channel_error_retry: True

Environment

Python: 3.13

What Broke

Users experienced crashes when using a list of broker URLs with quorum queues.

Why It Broke

The code attempted to call 'strip' on a list instead of a string

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install celery==5.5.1

When NOT to use: This fix should not be applied if the broker URLs are guaranteed to be strings.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/celery/celery/pull/9657

First fixed release: 5.5.1

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the broker URLs are guaranteed to be strings.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Track RSS + object counts after deployments; alert on monotonic growth and GC pressure.
Add a long-running test that repeats the failing call path and asserts stable memory.

Version Compatibility Table

Version	Status
5.5.1	Fixed

Related Issues

No related fixes found.

Cluster: celery:configuration-error Celery hub Celery best practices All hubs All clusters

Related clusters: Data consistency Duplicates Duplicate processing

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Celery RabbitMQ Quorum queues with a list of `broker_url` - AttributeError: 'list' object has no (Fix)