Handling retriable and non-retriable pod failures with Pod failure policy

FEATURE STATE: Kubernetes v1.26 [beta]

This document shows you how to use the Pod failure policy, in combination with the default Pod backoff failure policy, to improve the control over the handling of container- or Pod-level failure within a Job.

The definition of Pod failure policy may help you to:

  • better utilize the computational resources by avoiding unnecessary Pod retries.
  • avoid Job failures due to Pod disruptions (such preemption, API-initiated eviction or taint-based eviction).

Before you begin

You should already be familiar with the basic use of Job.

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

Your Kubernetes server must be at or later than version v1.25. To check the version, enter kubectl version.

Ensure that the feature gates PodDisruptionConditions and JobPodFailurePolicy are both enabled in your cluster.

Using Pod failure policy to avoid unnecessary Pod retries

With the following example, you can learn how to use Pod failure policy to avoid unnecessary Pod restarts when a Pod failure indicates a non-retriable software bug.

First, create a Job based on the config:

/controllers/job-pod-failure-policy-failjob.yamlHandling retriable and non-retriable pod failures with Pod failure policy - 图1

  1. apiVersion: batch/v1
  2. kind: Job
  3. metadata:
  4.   name: job-pod-failure-policy-failjob
  5. spec:
  6.   completions: 8
  7.   parallelism: 2
  8.   template:
  9.     spec:
  10.       restartPolicy: Never
  11.       containers:
  12.       - name: main
  13.         image: docker.io/library/bash:5
  14.         command: ["bash"]
  15.         args:
  16.         - -c
  17.         - echo "Hello world! I'm going to exit with 42 to simulate a software bug." && sleep 30 && exit 42
  18.   backoffLimit: 6
  19.   podFailurePolicy:
  20.     rules:
  21.     - action: FailJob
  22.       onExitCodes:
  23.         containerName: main
  24.         operator: In
  25.         values: [42]

by running:

  1. kubectl create -f job-pod-failure-policy-failjob.yaml

After around 30s the entire Job should be terminated. Inspect the status of the Job by running:

  1. kubectl get jobs -l job-name=job-pod-failure-policy-failjob -o yaml

In the Job status, see a job Failed condition with the field reason equal PodFailurePolicy. Additionally, the message field contains a more detailed information about the Job termination, such as: Container main for pod default/job-pod-failure-policy-failjob-8ckj8 failed with exit code 42 matching FailJob rule at index 0.

For comparison, if the Pod failure policy was disabled it would take 6 retries of the Pod, taking at least 2 minutes.

Clean up

Delete the Job you created:

  1. kubectl delete jobs/job-pod-failure-policy-failjob

The cluster automatically cleans up the Pods.

Using Pod failure policy to ignore Pod disruptions

With the following example, you can learn how to use Pod failure policy to ignore Pod disruptions from incrementing the Pod retry counter towards the .spec.backoffLimit limit.

Caution: Timing is important for this example, so you may want to read the steps before execution. In order to trigger a Pod disruption it is important to drain the node while the Pod is running on it (within 90s since the Pod is scheduled).

  1. Create a Job based on the config:

    /controllers/job-pod-failure-policy-ignore.yamlHandling retriable and non-retriable pod failures with Pod failure policy - 图2

    1. apiVersion: batch/v1
    2. kind: Job
    3. metadata:
    4.   name: job-pod-failure-policy-ignore
    5. spec:
    6.   completions: 4
    7.   parallelism: 2
    8.   template:
    9.     spec:
    10.       restartPolicy: Never
    11.       containers:
    12.       - name: main
    13.         image: docker.io/library/bash:5
    14.         command: ["bash"]
    15.         args:
    16.         - -c
    17.         - echo "Hello world! I'm going to exit with 0 (success)." && sleep 90 && exit 0
    18.   backoffLimit: 0
    19.   podFailurePolicy:
    20.     rules:
    21.     - action: Ignore
    22.       onPodConditions:
    23.       - type: DisruptionTarget

    by running:

    1. kubectl create -f job-pod-failure-policy-ignore.yaml

  2. Run this command to check the nodeName the Pod is scheduled to:

    1. nodeName=$(kubectl get pods -l job-name=job-pod-failure-policy-ignore -o jsonpath='{.items[0].spec.nodeName}')

  3. Drain the node to evict the Pod before it completes (within 90s):

    1. kubectl drain nodes/$nodeName --ignore-daemonsets --grace-period=0

  4. Inspect the .status.failed to check the counter for the Job is not incremented:

    1. kubectl get jobs -l job-name=job-pod-failure-policy-ignore -o yaml

  5. Uncordon the node:

    1. kubectl uncordon nodes/$nodeName

The Job resumes and succeeds.

For comparison, if the Pod failure policy was disabled the Pod disruption would result in terminating the entire Job (as the .spec.backoffLimit is set to 0).

Cleaning up

Delete the Job you created:

  1. kubectl delete jobs/job-pod-failure-policy-ignore

The cluster automatically cleans up the Pods.

Using Pod failure policy to avoid unnecessary Pod retries based on custom Pod Conditions

With the following example, you can learn how to use Pod failure policy to avoid unnecessary Pod restarts based on custom Pod Conditions.

Note: The example below works since version 1.27 as it relies on transitioning of deleted pods, in the Pending phase, to a terminal phase (see: Pod Phase).

  1. First, create a Job based on the config:

    /controllers/job-pod-failure-policy-config-issue.yamlHandling retriable and non-retriable pod failures with Pod failure policy - 图3

    1. apiVersion: batch/v1
    2. kind: Job
    3. metadata:
    4.   name: job-pod-failure-policy-config-issue
    5. spec:
    6.   completions: 8
    7.   parallelism: 2
    8.   template:
    9.     spec:
    10.       restartPolicy: Never
    11.       containers:
    12.       - name: main
    13.         image: "non-existing-repo/non-existing-image:example"
    14.   backoffLimit: 6
    15.   podFailurePolicy:
    16.     rules:
    17.     - action: FailJob
    18.       onPodConditions:
    19.       - type: ConfigIssue

    by running:

    1. kubectl create -f job-pod-failure-policy-config-issue.yaml

    Note that, the image is misconfigured, as it does not exist.

  2. Inspect the status of the job’s Pods by running:

    1. kubectl get pods -l job-name=job-pod-failure-policy-config-issue -o yaml

    You will see output similar to this:

    1. containerStatuses:
    2. - image: non-existing-repo/non-existing-image:example
    3.    ...
    4.    state:
    5.    waiting:
    6.       message: Back-off pulling image "non-existing-repo/non-existing-image:example"
    7.       reason: ImagePullBackOff
    8.       ...
    9. phase: Pending

    Note that the pod remains in the Pending phase as it fails to pull the misconfigured image. This, in principle, could be a transient issue and the image could get pulled. However, in this case, the image does not exist so we indicate this fact by a custom condition.

  3. Add the custom condition. First prepare the patch by running:

    1. cat <<EOF > patch.yaml
    2. status:
    3.   conditions:
    4.   - type: ConfigIssue
    5.     status: "True"
    6.     reason: "NonExistingImage"
    7.     lastTransitionTime: "$(date -u +"%Y-%m-%dT%H:%M:%SZ")"
    8. EOF

    Second, select one of the pods created by the job by running:

    1. podName=$(kubectl get pods -l job-name=job-pod-failure-policy-config-issue -o jsonpath='{.items[0].metadata.name}')

    Then, apply the patch on one of the pods by running the following command:

    1. kubectl patch pod $podName --subresource=status --patch-file=patch.yaml

    If applied successfully, you will get a notification like this:

    1. pod/job-pod-failure-policy-config-issue-k6pvp patched

  4. Delete the pod to transition it to Failed phase, by running the command:

    1. kubectl delete pods/$podName

  5. Inspect the status of the Job by running:

    1. kubectl get jobs -l job-name=job-pod-failure-policy-config-issue -o yaml

    In the Job status, see a job Failed condition with the field reason equal PodFailurePolicy. Additionally, the message field contains a more detailed information about the Job termination, such as: Pod default/job-pod-failure-policy-config-issue-k6pvp has condition ConfigIssue matching FailJob rule at index 0.

Note: In a production environment, the steps 3 and 4 should be automated by a user-provided controller.

Cleaning up

Delete the Job you created:

  1. kubectl delete jobs/job-pod-failure-policy-config-issue

The cluster automatically cleans up the Pods.

Alternatives

You could rely solely on the Pod backoff failure policy, by specifying the Job’s .spec.backoffLimit field. However, in many situations it is problematic to find a balance between setting a low value for .spec.backoffLimit to avoid unnecessary Pod retries, yet high enough to make sure the Job would not be terminated by Pod disruptions.