Fail fast for unrecoverable Kubernetes jobs

[GWphua]

Description

Currently, Kubernetes jobs will retry for a total of 10 times to create a peon pod for ingestion tasks. However, there are some pain points that surface during periods of heavy configuration, or when starting new clusters using similar Druid helm charts (copy-paste):

1. The error Error when looking for K8s pod with label[job-name=%s] is not useful for us. We will need to further discover what is going on by doing kubectl describe job ${jobname}.
2. Given the 10 retries for pod creation, along with Kubernetes exponential backoff, jobs will be pending for ~2minutes before failing and giving the above-mentioned logs.

This PR improves error handling and retry logic in druid-kubernetes-overlord-extension when the Kubernetes job fails to create peon pods.

Enhanced Error Handling for Pod Creation Failures

1. Provides more descriptive error messages that include the related job's latest Kubernetes event message.
2. Better error categorization using DruidException with appropriate persona (OPERATOR) and category (NOT_FOUND)

Important Note: You (or K8s Operators) will need to allow event logging for Druid service accounts to allow the fail-fast feature to work properly.

If you somehow forget to allow event logging for your Druid service account, the behaviour of jobs that successfully spin up pods will not be affected, but you will get a warning Failed to get events for job[%s] and receive the old K8s pod with label[job-name=%s] not found"message.

Improved Retry Logic using Blacklisted Error Message

Implements intelligent retry logic that avoids retrying when the failure is due to known unrecoverable conditions. A list of unrecoverable event message substrings are specified under BLACKLISTED_PEON_POD_ERROR_MESSAGES. The shouldRetryStartingPeonPod() method checks exception messages (in the form of Kubernetes Job event messages) against this blacklist to determine if retrying would be futile.

BLACKLISTED_PEON_POD_ERROR_MESSAGES currently includes: "max limit to request ratio" - which catches failures when resource (cpu, memory, etc.) request-limits ratio is beyond the allowable amount.

This is how the exception message will look like now:

Job[XXX] failed to start up pods. Latest event: [Error creating: pods "XXX" is forbidden: memory max limit to request ratio per Container is 1, but provided ratio is 1.333333]

I have only added one event message substring that really hits me very often. Feel free to add upon this constant should you discover more unrecoverable issues (or even allow this list to be configurable?).

Release note

Kubernetes jobs will have clearer failure messages during pod creation, and will fail fast under unrecoverable conditions.

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Key changed/added classes in this PR

• KubernetesPeonClient.java
• DruidK8sConstants.java
• KubernetesPeonClientTest.java

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This PR has:

• [x] been self-reviewed.
• [x] added documentation for new or modified features or behaviors.
• [x] a release note entry in the PR description.
• [x] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• [x] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• [x] added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• [x] been tested in a test Druid cluster.