Dennis-Mircea opened a new pull request, #1081:
URL: https://github.com/apache/flink-kubernetes-operator/pull/1081
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## What is the purpose of the change
JIRA: [FLINK-39390](https://issues.apache.org/jira/browse/FLINK-39390)
This PR enables plugin-based extensibility for the built-in Kubernetes
Operator autoscaler components (`ScalingRealizer`, `AutoScalerStateStore`,
`AutoScalerEventHandler`, `KubernetesJobAutoScalerContext`), using the same
`PluginUtils` mechanism already in place for `FlinkResourceListener`,
`FlinkResourceMutator`, and `FlinkResourceValidator`.
Previously, customizing these components required forking the operator. With
this change, users can drop plugin JARs into the operator's plugin directory
and have them discovered automatically at startup.
## Brief change log
**Core changes:**
- **`AutoscalerUtils`** *(new)* - Introduces the
`discoverOrDefault(Configuration, Class<T>, Supplier<T>)` utility that attempts
SPI discovery via `PluginUtils` and falls back to a default supplier. Logs
which implementation is used and warns if multiple are found.
- **`AutoscalerFactory`** - Now accepts a `FlinkConfigManager` parameter and
uses `discoverOrDefault` to resolve `AutoScalerStateStore`,
`AutoScalerEventHandler`, and `ScalingRealizer` instead of hardcoding the
Kubernetes defaults.
- **`FlinkResourceContext`** - `createJobAutoScalerContext()` now uses
`discoverOrDefault` to allow custom `KubernetesJobAutoScalerContext` subclasses
to be discovered from the plugin directory.
- **`FlinkOperator`** - Updated both `AutoscalerFactory.create()` call sites
(FlinkDeployment and FlinkSessionJob) to pass the `FlinkConfigManager`.
**Test changes:**
- **`AutoscalerUtilsTest`** *(new)* - 3 tests covering default fallback,
plugin discovery, and multiple-implementation scenarios.
- **`AutoscalerFactoryTest`** - 6 tests (default + custom plugin for each of
the 3 components). Extracted `withCustomPlugins(ThrowingRunnable)` helper to
eliminate duplicated env setup across custom plugin tests.
- **`FlinkResourceContextTest`** - 3 new tests: default context type,
caching behavior, and custom context discovery via plugin.
- **Test SPI implementations** *(new)* - `TestAutoScalerStateStore`,
`TestAutoScalerEventHandler`, `TestScalingRealizer`, `TestJobAutoScalerContext`
with corresponding `META-INF/services/` files and assembly descriptor entries.
- **`TestingFlinkDeploymentController`** - Updated
`AutoscalerFactory.create()` call to include `FlinkConfigManager`.
**Documentation:**
- **`autoscaler.md`** - Updated the "Extensibility of Autoscaler" section
with sub-bullets showing both Kubernetes Operator and Autoscaler Standalone
defaults for each interface. Added info hint about
`KubernetesJobAutoScalerContext` tight coupling and plugin scope. The
"Extensibility of Autoscaler" section was moved to the end as it covers both
build-in and standalone implementations.
- **`plugins.md`** - Added new "Custom Autoscaler Components" section with
interface descriptions, step-by-step guide, code example, directory structure,
and hints.
- Both English and Chinese (`content.zh/`) docs are updated.
## Verifying this change
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This change is not breaking any existent tests and is covered by **12 new
tests** and existing tests:
- Added a new test class called `AutoscalerUtilsTest` with the
`testDefaultFallback`, `testPluginDiscovery`, and
`testMultipleImplementationsUsesFirst` UTs to cover the functionality of
`AutoscalerUtils` new class
- Extended UT support for `AutoscalerFactoryTest` by adding
`testDefaultStateStore`, `testCustomStateStore`, `testDefaultEventHandler`,
`testCustomEventHandler`, `testDefaultScalingRealizer`, and
`testCustomScalingRealizer`.
- Extended UT support for `FlinkResourceContextTest` by adding
`testDefaultJobAutoScalerContext`, `testJobAutoScalerContextIsCached`, and
`testCustomJobAutoScalerContext`.
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): no
- The public API, i.e., is any changes to the `CustomResourceDescriptors`:
no
- Core observer or reconciler logic that is regularly executed: no
## Documentation
- Does this pull request introduce a new feature? yes
- If yes, how is the feature documented? docs
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