afedulov opened a new pull request #11195: [FLINK-16222][runtime] Use plugins mechanism for initializing MetricReporters URL: https://github.com/apache/flink/pull/11195 ## What is the purpose of the change [FLINK-11952](https://issues.apache.org/jira/browse/FLINK-11952) introduced Plugins mechanism into Flink. This PR makes it possible to benefit from using this new functionality during the MetricReporters initialization. Instead of placing MetricReporters JARs into`/libs`, it is now additionally possible (and encouraged) to convert them into plugins and use the `/plugins` folder for initialization via independent plugin classloaders. Note that to enable this functionality, a bounded type of Plugin was removed from the PluginLoader/PluginManager methods. This removal did not affect any existing functionality, including FileSystems initialization. The adjustment was required for the following reason: `MetricReporter` interface, which is located in the `flink-metrics-core` module is currently not a `Plugin`. `Plugin` interface is located in `flink-core` and this module already has a depency on `flink-metrics-core`. This makes in impossible to mark `MetricReporter` as `Plugin` without introducing a circular dependency. An alternative approach could be extraction of the whole plugin classloading functionality out of `flink-core` into a separate module. Another important consideration - current `PluginClassLoader` implementation uses parent-first initialization for classes, which start with Flink-native package prefixes, such as *org.apache.flink.*. Currently, metrics reporters shipped with Flink all have the same package prefix. This leads to the following situation: if there is a version of `PluginMetricFactory` for a particular reporter found in the /lib folder, JARs for this reporter in /plugins directory will effectively be ignored. The opposite priority might actually be desirable to improve user's experience when transitioning to plugins-based metrics initialization approach. ## Brief change log - `PluginManager`, already created for `FileSystems` initialization, is propagated from all Flink entrypoints into metrics reporters initializer - Reporters initializer (`ReporterSetup`) combines initialization via existing `ServiceLoader` approach with the new approach of loading plugins - `PrometheusReporter` is adjusted to be compatible with the new plugins mechanism. Proper functioning is verified with the end-to-end tests ## Verifying this change This change added tests and can be verified as follows: - Added integration tests for end-to-end tests ## 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 changed class annotated with `@Public(Evolving)`: (no) - The serializers: (no) - The runtime per-record code paths (performance sensitive): (no) - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: (yes) - The S3 file system connector: (no) ## Documentation - Does this pull request introduce a new feature? (yes) - If yes, how is the feature documented? (not documented)
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