Debug Running Pods

This page explains how to debug Pods running (or crashing) on a Node.

Before you begin

  • Your Pod should already be scheduled and running. If your Pod is not yet running, start with Troubleshoot Applications.
  • For some of the advanced debugging steps you need to know on which Node the Pod is running and have shell access to run commands on that Node. You don't need that access to run the standard debug steps that use kubectl.

Examining pod logs

First, look at the logs of the affected 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}

Debugging with container exec

If the container image includes debugging utilities, as is the case with images built from Linux and Windows OS base images, you can run commands inside a specific container with kubectl exec:

kubectl exec ${POD_NAME} -c ${CONTAINER_NAME} -- ${CMD} ${ARG1} ${ARG2} ... ${ARGN}
Note: -c ${CONTAINER_NAME} is optional. You can omit it 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

You can run a shell that's connected to your terminal using the -i and -t arguments to kubectl exec, for example:

kubectl exec -it cassandra -- sh

For more details, see Get a Shell to a Running Container.

Debugging with an ephemeral debug container

FEATURE STATE: Kubernetes v1.18 [alpha]

Ephemeral containers are useful for interactive troubleshooting when kubectl exec is insufficient because a container has crashed or a container image doesn't include debugging utilities, such as with distroless images. kubectl has an alpha command that can create ephemeral containers for debugging beginning with version v1.18.

Example debugging using ephemeral containers

Note: The examples in this section require the EphemeralContainers feature gate enabled in your cluster and kubectl version v1.18 or later.

You can use the kubectl alpha debug command to add ephemeral containers to a running Pod. First, create a pod for the example:

kubectl run ephemeral-demo --restart=Never
Note: This section use the pause container image in examples because it does not contain userland debugging utilities, but this method works with all container images.

If you attempt to use kubectl exec to create a shell you will see an error because there is no shell in this container image.

kubectl exec -it ephemeral-demo -- sh
OCI runtime exec failed: exec failed: container_linux.go:346: starting container process caused "exec: \"sh\": executable file not found in $PATH": unknown

You can instead add a debugging container using kubectl alpha debug. If you specify the -i/--interactive argument, kubectl will automatically attach to the console of the Ephemeral Container.

kubectl alpha debug -it ephemeral-demo --image=busybox --target=ephemeral-demo
Defaulting debug container name to debugger-8xzrl.
If you don't see a command prompt, try pressing enter.
/ #

This command adds a new busybox container and attaches to it. The --target parameter targets the process namespace of another container. It's necessary here because kubectl run does not enable process namespace sharing in the pod it creates.

Note: The --target parameter must be supported by the Container Runtime. When not supported, the Ephemeral Container may not be started, or it may be started with an isolated process namespace.

You can view the state of the newly created ephemeral container using kubectl describe:

kubectl describe pod ephemeral-demo
Ephemeral Containers:
    Container ID:   docker://b888f9adfd15bd5739fefaa39e1df4dd3c617b9902082b1cfdc29c4028ffb2eb
    Image:          busybox
    Image ID:       docker-pullable://busybox@sha256:1828edd60c5efd34b2bf5dd3282ec0cc04d47b2ff9caa0b6d4f07a21d1c08084
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Wed, 12 Feb 2020 14:25:42 +0100
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:         <none>

Use kubectl delete to remove the Pod when you're finished:

kubectl delete pod ephemeral-demo

Debugging via a shell on the node

If none of these approaches work, you can find the host machine that the pod is running on and SSH into that host, but this should generally not be necessary given tools in the Kubernetes API. Therefore, if you find yourself needing to ssh into a machine, please file a feature request on GitHub describing your use case and why these tools are insufficient.

Last modified May 30, 2020 at 3:10 PM PST: add en pages (ecc27bbbe)