Extend logging handling and exposure

[cdprete]

Hello.

For Spring Boot 4, I would like to suggest the following modifications and/or extensions around the Spring Boot Logging system:

• as already happens since years with Lo4j2 and Logback, Spring Boot Logging should allow to configure multiple appenders that can potentially log to different files or get triggered on different log levels (e.g.: https://logback.qos.ch/manual/filters.html#thresholdFilter).
  • of course, external log files should then also be possible.
• the rolling strategies should be extended to allow also the rolling of the log files by time and not just by size
• the /logFile Actuator endpoint should be converted to:
  • /logFiles: returns a list of the log files currently handled, including rotated ones.
  • /logFiles/{filename}: return the chunked content of the selected log file as it's done today by /logFile.
• the /loggers/{name} endpoint should allow to change the log level also if the logging is configured externally (e.g.: logback.xml or log4j2.xml) and loaded by logging.config.
  Maybe it's already the case, but I fail to find some documentation that really explains it, since every example I found configures the logging directly in the application.yaml.

[wilkinsona]

Thanks for the suggestions.

configure multiple appenders that can potentially log to different files or get triggered on different log levels

You should use custom log configuration for this. It is too complex to configure through application properties.

the rolling strategies should be extended to allow also the rolling of the log files by time and not just by size

This is already possible. As described in Logback's documentation the time-based policy is inferred from the file name pattern. In Boot, that pattern can be configured using logging.logback.rollingpolicy.file-name-pattern

returns a list of the log files currently handled, including rotated ones.
return the chunked content of the selected log file as it's done today by /logFile.

There's no easy way for us to identify these files as Spring Boot knows nothing about them. Adding knowledge of them would couple the endpoint to a specific logging system, and expose it to significant complexity as files are renamed and deleted during rotation.

If you want access to historic log events, I would recommend exporting your logging over OTLP or the like.

the /loggers/{name} endpoint should allow to change the log level also if the logging is configured externally

This is already possible. If it required a particular configuration mechanism the documentation would state that was the case.

Thanks again for the suggestions. I'm going to close this one as I don't think there's anything to be done here.

[cdprete]

Thanks for the suggestions.

configure multiple appenders that can potentially log to different files or get triggered on different log levels

You should use custom log configuration for this. It is too complex to configure through application properties.

The idea is exactly to not do that, but configure everything in the app config file.

the rolling strategies should be extended to allow also the rolling of the log files by time and not just by size

This is already possible. As described in Logback's documentation the time-based policy is inferred from the file name pattern. In Boot, that pattern can be configured using logging.logback.rollingpolicy.file-name-pattern

Ah yeah. That's true.
I think the issue I had in the past is that you're forced to archive the rolled log files, which is not desirable in some cases.
But I need to double-check it.

returns a list of the log files currently handled, including rotated ones.
return the chunked content of the selected log file as it's done today by /logFile.

There's no easy way for us to identify these files as Spring Boot knows nothing about them. Adding knowledge of them would couple the endpoint to a specific logging system, and expose it to significant complexity as files are renamed and deleted during rotation.

Can't Spring Boot parse the logging configuration for this? You've anyway some coupling through logging.config somehow.

If you want access to historic log events, I would recommend exporting your logging over OTLP or the like.

Absolutely. But we're using Spring Boot Admin and it would be nice to have the possibility to see them there.

the /loggers/{name} endpoint should allow to change the log level also if the logging is configured externally

This is already possible. If it required a particular configuration mechanism the documentation would state that was the case.

Does it mean I can use it even with the logging system being configured externally?