## TL;DR
A workflow stuck in Running with no node progress usually means the workflow controller is overloaded, throttled, or out of memory: its work queue backs up and nodes never get processed. Check the controller's queue metrics and logs, relieve the pressure, and the workflow resumes.

## Error
```text
argo workflow stuck in Running: controller queue debugging
```

## Steps
1. Check the workflow's node status: describe the workflow and look at which nodes are pending and their messages. Expected: nodes waiting with no recent updates, pointing at the controller rather than the workload.
2. Inspect the controller: check the workflow-controller deployment's logs for errors, throttling, or OOM kills, and look at its queue-depth metrics. Expected: you see whether the queue is backed up or the controller is crashlooping.
3. Check controller resources: raise CPU and memory if it is throttled or OOMKilled, and check the parallelism and rate-limit settings. Expected: the controller has headroom.
4. Look for a poison workflow: one malformed workflow can wedge the queue; check for workflows with huge node counts or error loops. Expected: the offender identified and deleted or fixed.
5. Watch the stuck workflow after the fix. Expected: nodes start transitioning and the workflow completes.

## When to use
- Argo Workflows stuck in Running with no node progress
- Controller pods crashlooping or throttled
- After scaling up workflow volume

## When not to use
- Workflow template validation errors (fail fast, not stuck)
- Nodes running but slow (workload performance)

## Tool compatibility
- Argo Workflows controller; queue-depth metrics, controller logs

## Variant phrasings
### argo controller queue backed up
Scale the controller and check for poison workflows; the queue only drains as fast as the controller processes.

### workflow running forever argo
Distinguish controller stall (no node updates) from a genuinely long-running node.

## Why it happens
The workflow controller is a single reconciliation loop over a work queue: every node transition goes through it. Overload it (too many workflows, too little CPU, a poison entry) and the queue grows while workflows appear frozen, even though nothing is wrong with the workflow definitions.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_sDqcJCX3wJdLk_zjNRN3PQ