Status

Current state: Approved

Discussion thread: here

Vote thread: here

JIRA:

Motivation

All Kafka components register AppInfo metrics to track application details such as start time and commit-id etc. These metrics are valuable for monitoring and debugging. However, AppInfo does not include the client-id for Worker and MM2 clients, which is an important piece of information for custom metrics reporters. While most Kafka clients (consumer, producer, admin) already register their client-id in the metrics config, there are cases in MM2 and Worker where AppInfo is registered without the client-id.

The AppInfoParser class registers a JMX MBean with the provided client-id, but when adding metrics to the Metrics registry, the client-id is not included. This KIP proposes adding the client-id as a metric tag.

Public Interfaces

Currently MetricName for Worker and MM2 clients:

• [name=start-time-ms, group=app-info, description=Metric indicating start-time-ms, tags={}]
• [name=commit-id, group=app-info, description=Metric indicating commit-id, tags={}]
• [name=version, group=app-info, description=Metric indicating version, tags={}]

New MetricName for Worker and MM2 clients:

• [name=start-time-ms, group=app-info, description=Metric indicating start-time-ms, tags={client-id=<component-id>}]
• [name=commit-id, group=app-info, description=Metric indicating commit-id, tags={client-id=<component-id>}]
• [name=version, group=app-info, description=Metric indicating version, tags={client-id=<component-id>}]

Proposed Changes

1) The new MBean will include a new tag, client-id

private static void registerMetrics(Metrics metrics, AppInfo appInfo, String clientId) {
    if (metrics == null) return;
    // Most Kafka clients (producer/consumer/admin) set the client-id tag in the metrics config.
    // Although we don’t explicitly parse client-id here, these metrics are automatically tagged with client-id.
    metrics.addMetric(metricName(metrics, "version", Map.of()), (Gauge<String>) (config, now) -> appInfo.getVersion());
    metrics.addMetric(metricName(metrics, "commit-id", Map.of()), (Gauge<String>) (config, now) -> appInfo.getCommitId());
    metrics.addMetric(metricName(metrics, "start-time-ms", Map.of()), (Gauge<Long>) (config, now) -> appInfo.getStartTimeMs());
    // MirrorMaker/Worker doesn't set client-id tag into the metrics config, so we need to set it here.
    if (!metrics.config().tags().containsKey("client-id") && clientId != null) {
        metrics.addMetric(metricName(metrics, "version", Map.of("client-id", clientId)), (Gauge<String>) (config, now) -> appInfo.getVersion());
        metrics.addMetric(metricName(metrics, "commit-id", Map.of("client-id", clientId)), (Gauge<String>) (config, now) -> appInfo.getCommitId());
        metrics.addMetric(metricName(metrics, "start-time-ms", Map.of("client-id", clientId)), (Gauge<Long>) (config, now) -> appInfo.getStartTimeMs());
    }
}

2) When unregisters an MBean, also remove the new and deprecated MBean.

private static void unregisterMetrics(Metrics metrics, String clientId) {
    if (metrics == null) return;

    metrics.removeMetric(metricName(metrics, "version", Map.of()));
    metrics.removeMetric(metricName(metrics, "commit-id", Map.of()));
    metrics.removeMetric(metricName(metrics, "start-time-ms", Map.of()));

    if (!metrics.config().tags().containsKey("client-id") && clientId != null) {
        metrics.removeMetric(metricName(metrics, "version", Map.of("client-id", clientId)));
        metrics.removeMetric(metricName(metrics, "commit-id", Map.of("client-id", clientId)));
        metrics.removeMetric(metricName(metrics, "start-time-ms", Map.of("client-id", clientId)));
    }
}

Compatibility, Deprecation, and Migration Plan

For users currently relying on the metric name without client-id tag, it will remain available until Kafka 5.0. New users are encouraged to use the new metric name, which includes the client-id tag. This deprecation will be documented in upgrade.html.

In Kafka 5.0, the following metric name will be removed. 

• [name=start-time-ms, group=app-info, description=Metric indicating start-time-ms, tags={}]
• [name=commit-id, group=app-info, description=Metric indicating commit-id, tags={}]
• [name=version, group=app-info, description=Metric indicating version, tags={}]

Test Plan

change unit test or Integration test to verify the new method.

Rejected Alternatives

A new deprecated configuration could be introduced to control the registration of this MBean.

Nevertheless, this approach is considered unnecessary, as it would introduce complexity without significant benefit.