How to add a static field to gelf logstash appender in properties file? biz.paluch.logging

I am using GELF-logstash appender together with log4j2 as logging appender, to send logs from my application through logstash to ElasticSearch/Kibana.
In each log message I want to configure a static field, namely the region my application is deployed to, which is gathered from an environment variable differing by the region the application is running in.

I found out that Static Literals are supported by the XML configuration like this: <Field name="fieldName1" literal="your literal value" /> https://logging.paluch.biz/examples/log4j-2.x.html But I would like to stay with my log4j2.properties file based configuration if possible, but could not find a documentation to add a static literal there.

Solution

Yes, this is possible. You can use the pre-defined field facility, or define as many custom static fields as you wish in your log4j2.properties file:

# required configuration for GELF
appender.gelf.type = Gelf
appender.gelf.name = GELF
appender.gelf.host = ${sys:LOG_HOST}
appender.gelf.port = ${sys:LOG_PORT}

# pre-defined field facility
appender.gelf.facility = a_static_value

# custom static field using environment variable
appender.gelf.environment.type = Field
appender.gelf.environment.name = environment_logging_field_name
appender.gelf.environment.literal = ${sys:ENV_VAR_NAME}

# custom static field with static value
appender.gelf.secondfield.type = Field
appender.gelf.secondfield.name = fieldName
appender.gelf.secondfield.literal = your_value_here