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Status
Current state: Under discussion
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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Motivation
Currently, there exists a kafka.server:type=MetadataLoader,name=CurrentMetadataVersion metric which tells the operator the metadata version feature level for every node in a cluster. However, now that there several features with support beyond the metadata.version feature, adding a metric to display those features' levels would be helpful for monitoring upgrade/downgrade scenarios for clusters using those features. Additionally, adding metrics for the minimum and maximum supported feature levels of each node would be helpful for the operator to determine if a feature upgrade/downgrade is safe to perform.
Public Interfaces
Monitoring
Add a metric metrics for each production feature (i.e. metadata.version , kraft.version , transaction.version , group.version , eligible.leader.replicas.version , share.version, and streams.version ).
This can be accomplished via one generic "feature level" metric metrics that is are tagged by feature name. Using a generic metric metrics allows for new production features to automatically expose their feature level and supported feature levels going forward.
| Name | Type | Description |
|---|---|---|
| kafka.server:type=MetadataLoader,name=FinalizedLevel,featureName=X | Integer | The finalized value of the feature level for a feature named "X". |
| kafka.controller:type=KafkaController,name=MinimumSupportedLevel,featureName=X | Integer | The minimum supported feature level for a feature named "X" on the controller. |
| kafka.controller:type=KafkaController,name=MaximumSupportedLevel,featureName=X | Integer | The maximum supported feature level for a feature named "X" on the controller. |
| kafka.server:type=broker-metadata-metrics,name=minimum-supported-feature-level,featureName=X | Integer | The minimum supported feature level for a feature named "X" on the broker. |
kafka.server:type=broker-metadata-metrics,name=maximum-supported-feature-level,featureName=X | Integer | The maximum supported feature level for a feature named "X" on the broker. |
The FinalizedLevel metric will report the finalized feature level for each production feature. If the feature level is not set, the metric will return a value of 0, since that means the feature is not enabled.
Compatibility, Deprecation, and Migration Plan
We will deprecate the kafka.server:type=MetadataLoader,name=CurrentMetadataVersion metric since this per-feature tagged metric also exposes this value, and the previous metric can be removed starting in 5.0.
Test Plan
We will add junit tests to verify the new metrics.
Rejected Alternatives
Running kafka-feature describe on every node is one way to track feature level upgrades/downgrades, but it is not straightforward to monitor since it is not a metric.