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Custom logging

In a cases when you need to override default Metarank logging configuration, you may need to build a custom docker image, based on an original upstream one from Metarank.

Metarank uses the following entrypoint for the docker container:

#!/bin/bash

set -euxo pipefail
OPTS=${JAVA_OPTS:-"-Xmx1g -verbose:gc"}

exec /usr/bin/java $OPTS -cp "/app/*" ai.metarank.main.Main "$@"

So you should note the following configuration toggles here:

  • env variable JAVA_OPTS can be used to pass custom JVM flags, like path to a custom logger configuration.

  • by default Metarank loads all the JAR files found in the /app/ directory.

Example: logstash-logback-encoder

To enable structured logging via logstash-logback-encoder, you can build a custom Docker image with the following Dockerfile:

FROM metarank/metarank:0.7.9-amd64

# add logback configuration file to the image
ADD logback.xml /app/

# add the logstash-logback-encoder with all its runtime dependencies to the classpath
ADD https://repo1.maven.org/maven2/net/logstash/logback/logstash-logback-encoder/7.4/logstash-logback-encoder-7.4.jar /app/
ADD https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.16.0/jackson-core-2.16.0.jar /app/
ADD https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.16.0/jackson-databind-2.16.0.jar /app/

# override default logback configuration
ENV JAVA_OPTS="-Xmx1g -Dlogback.configurationFile=/app/logback.xml -Dlogback.debug=true"

Such a custom image will successfully load the custom conviguration with non-default appender:

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