GWphua opened a new pull request, #17738:
URL: https://github.com/apache/druid/pull/17738
### Description
This PR aims to allow task pods to run in a namespace different from the
rest of the cluster.
#### Running Kubernetes Task Pods in Another Namespace
Currently, Druid already supports running task pods in another namespace by
specifying `druid.indexer.runner.namespace: taskPodNamespace`. If we only have
one Druid cluster that spins all these task pods up, we will not need this PR.
However, running task pods from multiple clusters will be a problem. Let us
imagine this scenario:
1. We have two Druid clusters running in two seperate namespaces: C1 and C2.
2. Suppose we aim to run our task pods in another namespace X.
3. C1 and C2 overlord spins up task pods by creating peon jobs in namespace
X.
4. WLOG, when Overlord server in C1 decides to retrieve peon jobs, it will
receive jobs from BOTH C1 and C2.
5. C1 Overlord throws an error as it cannot process jobs from C2.
#### Dealing with Kubernetes Task Pods from Multiple Namespaces
The Overlord service filters peon jobs by labels. Hence, the intuition
behind this PR is to simply label the peon jobs (`druid.overlord.namespace=C1`)
so that the Overlord can filter jobs that are relevant to its cluster.
Hence, we introduce the new config:
`druid.indexer.runner.overlordNamespace`. Here's an usage example using the
above-mentioned namespaces C1 and X.
1. When not provided, Druid will assume that X = C1, and default to
`druid.indexer.runner.namespace`.
2. When we want to run task pods in X, we can set
`druid.indexer.runner.namespace: X` and
`druid.indexer.runner.overlordNamespace: C1`.
#### Documentation
Added documentation for running Kubernetes Task Pods in another namespace.
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You can now run task pods in a namespace different from the rest of the
cluster.
<hr>
##### Key changed/added classes in this PR
* `k8s-jobs.md`
* `KubernetesTaskRunnerConfig.java`
* `KubernetesTaskRunnerFactory.java`
* `KubernetesPeonClient.java`
* `K8sTaskAdapter.java`
* `PodTemplateTaskAdapter.java`
* `DruidK8sConstants.java`
* Relevant test files and YAML files containing expected output.
<hr>
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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 or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [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](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
- [x] been tested in a test Druid cluster.
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