Proposal : Jib CLI Jar Processing

Relevant Issue: #2796

Motivation

Allow users to containerize arbitrary jar files without having to integrate Jib into java build tools (maven and gradle) or use a .yaml jib cli buildfile.

Proposal Changes

Standard Jar

A standard jar can be containerized in two modes, exploded or packaged.

Exploded Mode

Achieved by calling jib jar ${JAR_NAME}.jar --target ${TARGET_REGISTRY} The default mode for containerizing a jar. It will explode a jar into the following layers:

• Dependencies Layer: Contains dependencies whose versions do not contain SNAPSHOT. Note that this layer will not be created if Class-Path is not present in the manifest.
• Snapshot-Dependencies Layer: Contains dependencies whose versions contain SNAPSHOT. Note that this layer will not be created if Class-Path is not present in the manifest.
• Resources Layer: Contains resources parsed from jar file. Note that it will also include MANIFEST.MF.
• Classes Layer: Contains classes parsed from jar file.

Entrypoint : java -cp /app/dependencies/:/app/explodedJar/ ${MAIN_CLASS}

Packaged Mode

Achieved by calling jib jar ${JAR_NAME}.jar --target ${TARGET_REGISTRY} --mode packaged. It will result in the following layers on the container:

• Dependencies Layer: Contains the dependencies derived from Class-Path in jar manifest. Note that this layer will not be created if Class-Path is not present in the manifest.
• Jar Layer: Contains the original jar.

Entrypoint : java -jar ${JAR_NAME}.jar

Spring-Boot Fat Jar

A Spring-Boot Fat Jar can be containerized in two modes, exploded or packaged.

Exploded Mode

Achieved by calling jib jar ${JAR_NAME}.jar --target ${TARGET_REGISTRY} The default mode for containerizing a jar. It will explode a jar according to what is specified in the layers.idx file of the jar, if present, or according to following format:

• Dependencies Layer: For a dependency whose version does not contain SNAPSHOT.
• Spring-Boot-Loader Layer: Contains jar loader classes.
• Snapshot-Dependencies Layer: For a dependency whose version contains SNAPSHOT.
• Resources Layer: Contains resources parsed from BOOT-INF/classes/ in the jar and META-INF/.
• Classes Layer: Contains classes parsed from BOOT-INF/classes/ in the jar.

Entrypoint : java -cp /app org.springframework.boot.loader.JarLauncher

Packaged Mode

Achieved by calling jib jar ${JAR_NAME}.jar --target ${TARGET_REGISTRY} --mode packaged It will containerize the jar as is. However, note that we highly recommend against using packaged mode for containerizing spring-boot fat jars.

Entrypoint: java -jar ${JAR_NAME}.jar

Optional Parameters

The jar command also provides the option to configure the parameters listed below.

    --from                    The base image to use
    --jvm-flags               JVM arguments, example: --jvm-flags=-Dmy.property=value,-Xshare:off.
    --expose                  Ports to expose on container, example: --expose=5000,7/udp.
    --volumes                 Directories on container to hold extra volumes,  example: --volumes=/var/log,/var/log2.
    --environment-variables   Environment variables to write into container, example: --environment-variables env1=env_value1,env2=env_value2.
    --labels                  Labels to write into container metadata, example: --labels=label1=value1,label2=value2.
-u, --user                    The user to run the container as, example: --user=myuser:mygroup.
    --image-format            Format of container, example --image-format=OCI. Overrides the default (Docker).
    --program-args            Program arguments for container entrypoint.
    --entrypoint              Entrypoint for container. Overrides the default entrypoint, example: --entrypoint='custom entrypoint'.
    --creation-time           The creation time of the container in milliseconds since epoch or iso8601 format. Overrides the default (1970-01-01T00:00:00Z).