Troubleshooting the Cluster Operator

Use this information to troubleshoot common problems with the RabbitMQ Cluster Kubernetes Operator.

Note, the following information may be helpful for "do it yourself" (DIY) RabbitMQ on Kubernetes deployments but such environments are not its primary focus.

Common Scenarios and Errors

Certain errors have dedicated sections:

RabbitMQ Cluster Fails to Deploy

After creating a RabbitMQ instance, it is not available within a few minutes and RabbitMQ pods are not running.

Common reasons for such failure are:

  • Insufficient CPU or memory in the cluster
  • Incorrect imagePullSecrets configuration. This prevents the image from being pulled from a Docker registry.
  • Incorrect storageClassName configuration.

Potential solution to resolve this issue:

  • Run kubectl describe pod POD-NAME to see if there are any warnings (eg. 0/1 nodes are available: 1 Insufficient memory.)
  • Correct the imagePullSecrets and storageClassName configurations. See imagePullSecrets, Persistence, and Update a RabbitMQ Instance.
  • If the issue persists after updating the above configurations, view the status of your RabbitMQ cluster resources by following in the procedure in Check the Status of an Instance

If deploying to a resource-constrained cluster (eg. local environments like kind or minikube), you may need to adjust CPU and/or memory limits of the cluster. Check the resource-limits example to see how to do this.

Pods Are Not Being Created

An error such as

pods POD-NAME is forbidden: unable to validate against any pod security policy: []

as an event of the underlying ReplicaSet of the Kubernetes Operator deployment, or as an event of the underlying StatefulSet of the RabbitmqCluster.

This occurs if pod security policy admission control is enabled for the Kubernetes cluster, but you have not created the necessary PodSecurityPolicy and corresponding role-based access control (RBAC) resources.

Potential solution is to create the PodSecurityPolicy and RBAC resources by following the procedure in Pod Security Policies.

Pods Restart on Startup

The RabbitMQ container might fail at Pod startup and log a message such as

epmd error for host rabbitmq-server-1.rabbitmq-nodes.mynamespace: nxdomain (non-existing domain)

or

Error during startup: {error,no_epmd_port}

The Pod restarts and becomes Ready eventually.

Since RabbitMQ nodes resolve their own and peer hostnames during boot, CoreDNS caching timeout may need to be decreased from default 30 seconds to a value in the 5-10 seconds range.

Pods in CrashLoopBackOff State

Since Kubernetes restarts failing pods, if a RabbitMQ node can't start, it will likely enter the CrashLoopBackOff state - it attempts to start, fails and is restarted again. In such situations it might be hard to debug or fix the problem, if that requires accessing the pod or its data.

In some cases, you know you can fix the problem by starting a fresh node, which will synchronise everything from the other nodes in the cluster. Here's how you can do that:

The procedure below completely deletes a pod (RabbitMQ node) and its disk. This means the data from that node will be lost. Make sure you understand the consequences.

  1. kubectl rabbitmq pause-reconciliation RMQ_NAME (or add a label if you don't have the kubectl-rabbitmq plugin/CLI) - this means the Operator won't "fix" (overwrite) manual changes to the underlying objects
  2. kubectl delete statefulset --cascade=orphan RMQ_NAME-server - delete the statefulset so that it doesn't "fix" the pods (recreate the missing pod after we delete it)
  3. kubectl delete pod RMQ_SERVER-server-2 (you can delete any pod you want here)
  4. kubectl delete pvc RMQ_NAME-server-2
  5. kubectl delete pv PV_NAME if needed (this will completely delete the previous disk/data)
  6. kubectl rabbitmq resume-reconciliation RMQ_NAME (or delete the label) - the Operator fixes the deployment by recreating the StatefulSet and the StatefulSet recreates the missing pod and PVC

You can adapt this procedure to other situations as well - for example rather than deleting the disk, you can start a pod and attach the volume to investigate the contents.

The only RabbitMQ specific parts of this process are the first and last steps. Leran more about pausing RabbitmqCluster reconciliation. The other commands are common Kubernetes administration tasks.

Pods Are Stuck in the Terminating State

symptom: "After deleting a RabbitmqCluster instance, some Pods are stuck in the terminating state. RabbitMQ is still running in the affected Pods."

cause: "The likely cause is a leftover quorum queue in RabbitMQ."

Potential solution to resolve this issue:

  • Ensure there are no messages in the queue, or that it is acceptable to delete those messages.
  • Delete the queue by force by running:
kubectl delete pod --force --grace-period=0 POD-NAME

This example uses a Pod name:

kubectl delete pod --force rabbit-rollout-restart-server-1
# warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
# pod 'rabbit-rollout-restart-server-1' force deleted

Check the Status of an Instance

To view the status of an instance by running, use

kubectl -n NAMESPACE get all

Where NAMESPACE is the Kubernetes namespace of the instance.

For example:

kubectl -n rmq-instance-1 get all
# NAME                   READY   STATUS    RESTARTS   AGE
# pod/example-server-0   1/1      Running   0          2m27s

# NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE # service/example-nodes ClusterIP None None 4369/TCP 2m27s # service/example ClusterIP 10.111.202.183 None 5672/TCP,15672/TCP,15692/TCP 2m28s
# NAME READY AGE # statefulset.apps/example-server 1/1 2m28s

Cluster Operator Fails on Startup

After deploying RabbitMQ Cluster Operator, it fails during startup and its pod is restarted.

Common reasons for such failure are:

  • The Operator can't connect to the Kubernetes API.

Potential solution to resolve this issue:

  • Check whether the Operator is still crashing. Pod restarts solve many interim issues and therefore a restart is a symptom, not a problem.
  • Check the Operator logs (kubectl -n rabbitmq-system logs -l app.kubernetes.io/name=rabbitmq-cluster-operator)
  • You may see an error such as:
    • Failed to get API Group-Resources
    • Get https://ADDRESS:443/api: connect: connection refused
  • Check whether your Kubernetes cluster is healthy, specifically the kube-apiserver component
  • Check whether any security network policies could prevent the Operator from reaching the Kubernetes API server

RabbitMQ cluster status conditions

A RabbitMQ instance has status.conditions that describe the current state of the RabbitMQ cluster. To get the status, run:

kubectl describe rmq RMQ_NAME

Example status conditions may look like:

Name:         test-rabbit
Namespace:    rabbitmq-system
API Version:  rabbitmq.com/v1beta1
Kind:         RabbitmqCluster
...
Status:
  Binding:
    Name:  sample-default-user
  Conditions:
    Last Transition Time:  2023-07-07T11:57:10Z
    Reason:                AllPodsAreReady
    Status:                True
    Type:                  AllReplicasReady # true when all RabbitMQ pods are 'ready'
    Last Transition Time:  2023-07-07T11:57:10Z
    Reason:                AtLeastOneEndpointAvailable
    Status:                True
    Type:                  ClusterAvailable # true when at least one RabbitMQ pod is 'ready'
    Last Transition Time:  2023-07-07T11:55:58Z
    Reason:                NoWarnings
    Status:                True
    Type:                  NoWarnings
    Last Transition Time:  2023-07-07T11:57:11Z
    Message:               Finish reconciling
    Reason:                Success
    Status:                True
    Type:                  ReconcileSuccess
...

If the status condition ReconcileSuccess is false, that means the last reconcile has errored and RabbitMQ cluster configuration could be out of date. Checking out Cluster Operator logs is useful to understand why reconcile failed.

To get Operator logs:

kubectl -n rabbitmq-system logs -l app.kubernetes.io/name=rabbitmq-cluster-operator
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