ERROR No appender references provided to AsyncAppender: appenderRefs

[virajjasani]

Description

Using log4j2.properties to define AsyncAppender and have RFA added to the AsyncAppender. Somehow the appender ref is not correctly getting identified and hence it's resulting in error.

Configuration

Version: 2.17.2

Operating system: MacOS 13.2

JDK: 1.8.0_341

log4j2.properties:

appender.DRFA.type = RollingFile
appender.DRFA.name = DRFA
appender.DRFA.fileName = xyz
appender.DRFA.filePattern = xyz
appender.DRFA.createOnDemand = true
appender.DRFA.layout.type = PatternLayout
appender.DRFA.layout.pattern = %d{ISO8601} %-5p [%t] %c{2}: %.1000m%n
appender.DRFA.policies.type = Policies
appender.DRFA.policies.time.type = TimeBasedTriggeringPolicy
appender.DRFA.policies.time.interval = 1
appender.DRFA.policies.time.modulate = true
appender.DRFA.policies.size.type = SizeBasedTriggeringPolicy
appender.DRFA.policies.size.size = 256MB
appender.DRFA.strategy.type = DefaultRolloverStrategy
appender.DRFA.strategy.max = 20


appender.ASYA.type = Async
appender.ASYA.name = ASYA
appender.ASYA.appenderRefs = DRFA
appender.ASYA.blocking = true
appender.ASYA.bufferSize = 256

This results in error:

2023-01-26 00:58:07,944 main ERROR No appender references provided to AsyncAppender: appenderRefs
2023-01-26 00:58:07,951 main DEBUG AsyncAppender$Builder(={}, errorRef="null", blocking="true", shutdownTimeout="null", bufferSize="256", name="ASYA", includeLocation="null", Configuration(PropertiesConfig), ignoreExceptions="null", BlockingQueueFactory=null, Filter=null, ={})
2023-01-26 00:58:07,951 main ERROR Could not create plugin of type class org.apache.logging.log4j.core.appender.AsyncAppender for element Async org.apache.logging.log4j.core.config.ConfigurationException: Arguments given for element Async are invalid: field 'appenderRefs' has invalid value '[Lorg.apache.logging.log4j.core.config.AppenderRef;@35cabb2a'
    at org.apache.logging.log4j.core.config.plugins.util.PluginBuilder.injectFields(PluginBuilder.java:212)
    at org.apache.logging.log4j.core.config.plugins.util.PluginBuilder.build(PluginBuilder.java:123)
    at org.apache.logging.log4j.core.config.AbstractConfiguration.createPluginObject(AbstractConfiguration.java:1122)
...
...
... 

Tried these options but they are not able to attach ref:

appender.ASYA.appenderRefs.ref = DRFA
appender.ASYA.appenderRefs.DRFA.ref = DRFA
appender.ASYA = DRFA 

[ppkarwasz]

@virajjasani,

Try:

appender.ASYA.$0.type = AppenderRef
appender.ASYA.$0.ref = DRFA

You chose probably the worst configuration format available. Log4j2 configuration is hierarchical, which can not be said of the properties format. The properties format basically follows these rules:

• all properties and subcomponents of a Log4j2 component have the same prefix (in your case appender.ASYA for the asynchronous appender),
• simple properties are specified as prefix.property_name (e.g. appender.ASYA.blocking),
• subcomponents have a prefix of parent_prefix.unique_id (in my example appender.ASYA.$0), must have a type property (appender.ASYA.$0.type = AppenderRef in the example) and then you specify the subcomponent's properties as in the previous points.

Remark: some subcomponents, such as layouts or filters have a hardcoded unique id. Other parts of the configuration, like properties, follow slightly different rules.

[virajjasani]

Thanks @ppkarwasz. Yes looks like I got it wrong with hierarchical way for properties.

[virajjasani]

Closing the issue, thanks

[virajjasani]

@ppkarwasz

appender.ASYA.$0.type = AppenderRef
appender.ASYA.$0.ref = DRFA

Are you aware of log4j1.properties alternatives for the above?

log4j.appender.RFA=org.apache.log4j.RollingFileAppender
log4j.appender.RFA.File=${hadoop.log.dir}/datanode-metrics.log
log4j.appender.RFA.layout=org.apache.log4j.PatternLayout
log4j.appender.RFA.layout.ConversionPattern=%d{ISO8601} %m%n
log4j.appender.RFA.MaxBackupIndex=1
log4j.appender.RFA.MaxFileSize=64MB
log4j.appender.ASYNC=org.apache.log4j.AsyncAppender
log4j.appender.ASYNC.appender-ref=RFA
log4j.logger.classname=INFO,ASYNC
log4j.additivity.classname=false

I tried this but it says log4j:WARN No such property [appender-ref] in org.apache.log4j.AsyncAppender.

[ppkarwasz]

Check the AsyncAppender javadoc:

Important note: The AsyncAppender can only be script configured using the DOMConfigurator.

In the XML configuration you can use <appender-ref ref="..."/>.

Remark: Log4j 1.2 reached end-of-life almost 8 years ago. Several security vulnerabilities were discovered since then. You should not use it.

[virajjasani]

Important note: The AsyncAppender can only be script configured using the DOMConfigurator.

I see, thanks for the details. Looks like we might have to use AsyncAppenders together with RFA in that case (instead of applying RFA as appender ref to AsyncAppender).

Remark: Log4j 1.2 reached end-of-life almost 8 years ago. Several security vulnerabilities were discovered since then. You should not use it.

I agree, we are migrating from Log4J1 to Log4J2 only. However, as part of the big migration, we would be working on several sub-tasks. Since we use log4j.properties (rather than xml), we had added RFA to AsyncAppender programmatically. In order to avoid using org.apache.log4j.Logger directly, we need to replace them with slf4j. Before we do that, first I wanted to replace code that does asyncAppender.addAppender(rfaAppender) with log4j.properties in log4j1. Once this sub-task is done, as part of the overall migration, we can directly replace all log4j.properties to log4j2.properties in one shot.
Hence, I raised above question.

Thanks

[ppkarwasz]

@virajjasani,

Check our Log4j 1.2 to Log4j 2.x migration guide. Even if the original Log4j 1.2 does not support configuring an AsyncAppender through properties log4j-1.2-api does (the config you provided should work just fine).

... we need to replace them with slf4j.

No you don't, Log4j2 API provides everything SLF4J does and more. Check Remko's answer on SO from 5 years ago. Although SLF4J has introduced some features since then, Log4j2 API was not idling either.

If you have more question on the migration, I propose to continue this discussion on the log4j-user mailing list.

[virajjasani]

Thanks @ppkarwasz

[elDaniello]

@ppkarwasz thanks!