Log4j2 yml config do not support YAML Anchors and Aliases

[darkSheep404]

Description

Log4j2 yml config do not support YAML Anchors and Aliases with error Logger contains an invalid element or attribute "<<"

Configuration:
  status: WARN
  Appenders:
    RollingFileTemplate: &RollingFileTemplate
      ignoreExceptions: false
      PatternLayout:
        pattern: "[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%X{traceId},%X{spanId}] [%pid] [%thread] %-5level %X{class}.%M - %msg%n"
      Policies:
        SizeBasedTriggeringPolicy:
          size: "50 MB"
      DefaultRolloverStrategy:
        max: 200
    RollingFile:
      - name: XX_LOGGER_LOG
        fileName: ./logs/xx/${env:HOSTNAME:-}/app/app.log
        filePattern: "./logs/xx/${env:HOSTNAME:-}/app/app_%d{yyyy}-%i.log.gz"
        <<: *RollingFileTemplate
  Loggers:
    Root:
      level: INFO
      AppenderRef:
        - ref: CONSOLE_OUT_APPENDER
        - ref: XX_LOGGER_LOG

main ERROR Unable to locate plugin for LoggerTemplate
2025-01-06T08:35:01.514260458Z 2025-01-06 08:35:01,514 main ERROR Logger contains an invalid element or attribute "<<"
2025-01-06T08:35:01.514794013Z 2025-01-06 08:35:01,514 main ERROR Logger contains an invalid element or attribute "<<"
2025-01-06T08:35:01.515709563Z 2025-01-06 08:35:01,515 main ERROR Logger contains an invalid element or attribute "<<"
2025-01-06T08:35:01.516202917Z 2025-01-06 08:35:01,516 main ERROR Logger contains an invalid element or attribute "<<"
2025-01-06 08:35:01,516 main ERROR Unable to invoke factory method in class org.apache.logging.log4j.core.config.LoggersPlugin for element Loggers: java.lang.NullPointerException 

Configuration

Version: [2.18.0]

Operating system: [redheat]

JDK: [JDK 8 ]

Logs

[Stacktraces, errors, etc. relevant applications logs.]

Reproduction

[An isolated test reproducing the test.
JUnit tests similar to the ones in the code base are extremely appreciated.]

[ppkarwasz]

The YAML features that you can use in a Log4j configuration depend on the features supported by the parser we use.
Since the Jackson YAML data format module does not support the << merge key YAML extension, you can not use it in a Log4j configuration file. Log4j will automatically support merge keys, if FasterXML/jackson-dataformats-text#171 is ever implemented.

If you wish to use merge keys in a Log4j configuration file consider:

• contributing a PR to the Jackson project that solves com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "<<" (class com.wasiqb.config.DeviceSetting), not marked as ignorable FasterXML/jackson-dataformats-text#171. This is the preferred solution, since it does not require a change to the tree parser used by Log4j.
• or contributing an AbstractConfiguration implementation to Log4j that is based on SnakeYAML, which is the low-level parser used by Jackson. Since adding an additional direct dependency to Log4j has security implications, please discuss it on the dev@logging.apache.org mailing list first, if you choose this way.

Remark: Regardless of the support for merge keys, your configuration file would not work, since RollingFileTemplate is not a valid configuration snippet: it lacks the required name, fileName and filePattern attributes. This will always result in a configuration error, because Log4j Core interprets all the children of Appenders as appender definitions.

You should use something like this instead (again: assuming merge keys are supported by jackson-dataformat-yaml, which is not the case right now):

RollingFile:
  - &template
    name: FOO_LOG
    fileName: logs/foo.log
    filePattern: logs/foo.%i.log.gz
    ignoreExceptions: false
    PatternLayout:
      pattern: "%d [%t] %-5p %c{1.} - %m%n"
    Policies:
      SizeBasedTriggeringPolicy:
        size: "50 MB"
    DefaultRolloverStrategy:
      max: 200
  - <<: *template
    name: BAR_LOG
    fileName: logs/bar.log
    filePattern: logs/bar.%i.log.gz

[darkSheep404]

got it , many thx🙇🏻