Status

Current state: Accepted

Discussion thread: https://www.mail-archive.com/dev@kafka.apache.org/msg99656.html

Vote thread:

JIRA:  Unable to render Jira issues macro, execution error.

Released: 

Pull request: https://github.com/apache/kafka/pull/7403

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

Motivation

Kafka Connect does not provide an out-of-the-box facility to change log levels. When debugging connectors or the Connect framework, users have to update the log4j.properties file and restart the worker to see new logs. This is cumbersome in most cases, and restarting the worker sometimes hides bugs by resetting the internal state.

Proposed Changes

This change will introduce an /admin/loggers endpoint to the Connect worker that can be used to get/modify the log levels of any named loggers in the Connect worker. These modifications will not be persisted across worker restarts, and will only affect the worker whose endpoint received this REST request (other workers in the cluster will be unaffected). The /admin/loggers endpoint will support the following operations:

Get a list of all named loggers

Returns a list of loggers along with their current log levels. Entries are sorted by the logger's name. A named logger is one that is created by either the worker's classes using the LoggerFactory.getLogger method or is an ancestor denoted by the name of the package it corresponds to. Their levels are set by the log4j configuration file used by the worker JVM, or by using this API. 

$ curl -Ss http://localhost:8083/admin/loggers | jq
[
  ...
  "org.apache.kafka.connect.runtime.WorkerSinkTask": {
    "level": "INFO"
  },
  "org.apache.kafka.connect.runtime.WorkerSourceTask": {
    "level": "DEBUG"
  },
  ...
]

Get the log level of a specific logger

If the name of a logger is specified, only return the level to which that logger is writing messages at. This level may be set by a log4j configuration file, or by this API. If neither of those sources specified a level, log4j uses the level of an ancestor that was set by one of these means (the root logger's level is used if none of the other ancestor had a level set to it).

$ curl -Ss http://localhost:8083/admin/loggers/org.apache.kafka.connect.runtime.WorkerSinkTask | jq
{
   "level": "INFO"
}

Even if it is not used by any runtime classes to log any messages, requesting the level of an ancestor package will also return a log level using the above rules.

$ curl -Ss http://localhost:8083/admin/loggers/org.apache | jq
{
   "level": "INFO",
}

Set the log level of a specific logger

Use PUT to set the level of a logger. The API returns the list of loggers whose levels were modified.

$ curl -Ss -X PUT '{"level": "TRACE"}' http://localhost:8083/admin/loggers/org.apache.kafka.connect.runtime.WorkerSinkTask
{
  modified: [
    "org.apache.kafka.connect.runtime.WorkerSinkTask"
  ]
}

Setting the log level of an ancestor (for example, org.apache.kafka.connect as opposed to a classname) will update the levels of all child classes. Any levels previously set by this API will also be overridden. 

$ curl -Ss -X PUT '{"level": "TRACE"}' http://localhost:8083/admin/loggers/org.apache.kafka.connect
{
  modified: [
    ...
    "org.apache.kafka.connect.runtime.WorkerSinkTask",
    "org.apache.kafka.connect.runtime.WorkerSourceTask",
    ...
  ]
}

The above call returns org.apache.kafka.connect.runtime.WorkerSinkTask and org.apache.kafka.connect.runtime.WorkerSourceTask because they fall under the specified ancestor. If no name parameter is present, this API will set the log level of the root logger.

Configuration Changes

In addition, a new configuration property admin.listeners will be provided to specify which listener to use for the /admin endpoint. An additional configuration property will be used to control how the admin endpoint is made available.

Example Usage

Example 1: Disable the admin endpoints

Set a blank string to the admin.listeners property to disable the entire /admin endpoint.

admin.listeners=

Example 2: Use a separate listener for /admin 

Bring up the admin endpoint on a separate listener:

admin.listeners=http://localhost:9093

Example 3: Use a separate listener for /admin (https)

Set up SSL properties in a separate https listener:

admin.listeners=https://localhost:9093
admin.listeners.https.ssl.truststore.location=/path/to/truststore.jks
admin.listeners.https.ssl.truststore.password=tpass
admin.listeners.https.ssl.keystore.location=/path/to/keystore.jks
admin.listeners.https.ssl.keystore.password=kpass

Public Interfaces

• A /admin endpoint that can be configured to be attached to a different listener than the existing Connect endpoints.
• The /admin/loggers endpoint that be used to modify log levels.
• A new configuration property in WorkerConfig to enable/disable the /admin endpoint along with optionally configuring any HTTPS listeners if needed.

Log level changes are not persisted across worker restarts. These changes also only apply to the worker that receives the PUT request described above. 

Compatibility, Deprecation, and Migration Plan

This is a new feature. Existing features will not be changed.

It must be noted that the changes proposed only work when log4j 1.x is used to log messages and is available on classpath. This is the current default in the AK distribution as well. Other loggers (logback, log4j2 etc) will not be supported and this feature (and others mentioned below in related work) will have to be reworked to support these frameworks.

Rejected Alternatives

• Changing log levels in a single node of an application 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.
• Using JMX to change log levels is too cumbersome, difficult to secure and the other components are going to move away from it (look at KIP-412 where brokers are now using Admin Client to change log levels).

Related Work

• KIP-412: Extend Admin API to support dynamic application log levels
• KIP-449: Add connector contexts to Connect worker logs