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Status

Current state: Draft (WIP).

Discussion thread: here

Vote thread: here

JIRA: KAFKA-7772

Released: AK x.y.z

Pull Request: https://github.com/apache/kafka/pull/6069

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Connect currently does not offer a way to dynamically change log levels. This means debugging an issue with a connector or the framework can involve multiple cycles of "change log4j.properties file and restart connect". This proposal presents a feature to adjust log levels in Connect.

JMX based adjustments using kafka.utils.Log4jController 

Kafka core contains a Log4jController utility that allows log level adjustment from a JMX tool (jconsole or a rest interface using Jolokia). The screenshot below shows how JConsole can be used to navigate to the Kafka mbean, from where log levels can be found out using the getLogLevel operation, or set through setLogLevel. 

Proposed Approach

Even though Connect has a REST interface and it is probably easier to implement this through a simple Connect Rest Extension (requires no new additional configs or any setup steps), there is a lot of value in a consistent user experience. Hence, we propose the following approach:

  1. Rewrite the JMX logging utilities (kafka.utils.Log4jController) in Java, and move them from kafka-core to clients-common (the org.apache.kafka.common package in clients module), which holds other common utilities including but not limited to ConfigDef, Exceptions and Metrics. 
  2. Kafka and Connect depend on this module, and invoke helper functions that add "List Log Levels", "Set Log Level" and "Get Log Level" functionality into their JMX interface. 

Public Interfaces

Since there are standard tools to interface with JMX, we will not be adding any new tools or scripts to access this functionality.

Rejected Alternatives

  • Changing log levels in a single node of a component will affect other nodes in the cluster (for example, changing log level of a class in one Connect worker will update levels in all workers in a Connect cluster) and this new level will be persisted across node restarts. This is beyond the scope of this proposal.
  • Rest extensions were rejected, as Kafka doesn't offer a REST server.
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