Status

Current state: Under DiscussionRejected

Discussion thread: here (<- link to https://mail-archiveslists.apache.org/thread/n8omkpjf1mk9jphx38b8tfrs4h3nxo3zmod_mbox/flink-dev/)

JIRA:

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When this method is called by a ResourceManager, it does only one thing: changes the logging level on this task manager.

Logging Abstraction

The only thing Finally, the problem left is how the logging level is changed on a job manager or task managers. Although log4j2 is the default logging implementation that is included in the distribution libraries, other logging frameworks, including log4j1 and logback, are also recommended by the documentation "How to use logging". We need to have some kind of abstraction to not directly depend on the logging implementation. Provide interfaces The following interface and classes are introduced so that not only do they suit the currently supported ones but also we can have any other logging frameworks in the futureincluding the user-defined ones.

As illustrated by the class diagram above, the interface LogginerProvider is introduced where the setLogLevel() method varies among different logging implementations. The isEnabled() method is invoked during the initialization. All the LoggingProvider implementation classes, that are registered using the Java service loading facility, are tested and only the first enabled one will be used. Any subclass of the Slf4jLoggingProvider is considered to be enabled as long as the factory name returned from StaticLoggerBinder.getLoggerFactoryClassStr() is the same as the one of its logging implementation factory. If no one is enabled, NoOpLoggingProvider is used, and warning messages will be printed both duration initialization and when setLogLevel() method is called.

Supported Log Levels and Their Mappings

Here is the table of the corresponding native levels of all the supported logging implementations.

Limitations

TBD

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Test Plan

Describe in few sentences how the FLIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Rejected Alternatives

Considered to be an MVP (Minimal Viable Product), this improvement does not support the features, such as defining the scope (e.g. job manager or task manager only) and a timer. The log levels of the target logger are going to be changed cluster-wide, on the job manager leader and all the currently-registered task managers. To unset the previously-changed level, pass a null log-level argument.

Another limitation is that changing the log levels is not considered to be a persistent operation for simplicity. Without storing the log settings into a HighAvailabilityService, it is also impossible to change the log level on a follower job manager. If a task manager is (re-)joined or a standby job manager becomes the leader, the log levels on these processes remain unchanged and only will be changed upon the next call.

Compatibility, Deprecation, and Migration Plan

It does not affect any compatibility or have any deprecation or migration.

Test Plan

Besides unit tests, system tests will be included to cover the cases where different logging providers are used or no logging provider is enabled.

Rejected Alternatives

N/AIf there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.