Troubleshooting resources, frequently asked questions, and community support channels.

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Debugging Pods and Replication Controllers

Debugging pods

The first step in debugging a pod is taking a look at it. Check the current state of the pod and recent events with the following command:

$ kubectl describe pods ${POD_NAME}

Look at the state of the containers in the pod. Are they all Running? Have there been recent restarts?

Continue debugging depending on the state of the pods.

My pod stays pending

If a pod is stuck in Pending it means that it can not be scheduled onto a node. Generally this is because there are insufficient resources of one type or another that prevent scheduling. Look at the output of the kubectl describe ... command above. There should be messages from the scheduler about why it can not schedule your pod. Reasons include:

Insufficient resources

You may have exhausted the supply of CPU or Memory in your cluster. In this case you can try several things:

Using hostPort

When you bind a pod to a hostPort there are a limited number of places that the pod can be scheduled. In most cases, hostPort is unnecessary; try using a service object to expose your pod. If you do require hostPort then you can only schedule as many pods as there are nodes in your container cluster.

My pod stays waiting

If a pod is stuck in the Waiting state, then it has been scheduled to a worker node, but it can’t run on that machine. Again, the information from kubectl describe ... should be informative. The most common cause of Waiting pods is a failure to pull the image. There are three things to check:

My pod is crashing or otherwise unhealthy

First, take a look at the logs of the current container:

$ kubectl logs ${POD_NAME} ${CONTAINER_NAME}

If your container has previously crashed, you can access the previous container’s crash log with:

$ kubectl logs --previous ${POD_NAME} ${CONTAINER_NAME}

Alternately, you can run commands inside that container with exec:

$ kubectl exec ${POD_NAME} -c ${CONTAINER_NAME} -- ${CMD} ${ARG1} ${ARG2} ... ${ARGN}

Note that -c ${CONTAINER_NAME} is optional and can be omitted for pods that only contain a single container.

As an example, to look at the logs from a running Cassandra pod, you might run:

$ kubectl exec cassandra -- cat /var/log/cassandra/system.log

If none of these approaches work, you can find the host machine that the pod is running on and SSH into that host.

Debugging Replication Controllers

Replication controllers are fairly straightforward. They can either create pods or they can’t. If they can’t create pods, then please refer to the instructions above to debug your pods.

You can also use kubectl describe rc ${CONTROLLER_NAME} to inspect events related to the replication controller.


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