How to set JVM arguments when running mvn spring-boot:build-image command in Spring Boot 2.3.0 to generate a docker image?

Question

I am trying to build a docker image using the latest version of Spring Boot (2.3.0) . All I have to create an image now is run the command mvn:spring-boot:build-image . This will create a docker image for me. How do I set the JVM arguments (Max , Min heap sizes) in this case?

Answer 1

As of today, you can't set JVM arguments in spring-boot:build-image.

Spring boot build image uses Packeto internally and it accepts following 4 environment variables as mentioned in bellsoft-liberica GitHub.

"BP_JVM_VERSION" : "13.0.1",  
"BPL_JVM_HEAD_ROOM" : "10",
"BPL_JVM_LOADED_CLASS_COUNT" : "35", 
"BPL_JVM_THREAD_COUNT" : "10"

As alternate option, you can pass JVM arguments when you run the image.

docker run -p 8080:8080 --env JAVA_OPTS="-Xmx300m -Xms200m" -t youImageName

If using Kubernetes, you can configure JVM options at deployment level.

    spec:
      containers:
      - name: yourapp
        image: image path
        ports:
        - containerPort: 8080
        env:
        - name: SPRING_PROFILES_ACTIVE
          value: "prod"    
        - name: BPL_JVM_HEAD_ROOM
          value: "2"  
        - name: BPL_JVM_LOADED_CLASS_COUNT
          value: "35"  
        - name: BPL_JVM_THREAD_COUNT
          value: "10"  
        - name: JAVA_OPTS
          value: >-
                -XX:ReservedCodeCacheSize=40M
                -XX:MaxMetaspaceSize=60M
                -Xlog:gc
                -Xms34m
                -Xmx40m
                -Xss256k
                -XX:MaxRAM=150M

There's a GitHub issue open in Spring boot repository discussing this Failed to change JVM arguments for buildpacked image

Answer 2

Build Back Environment Variables

I tried setting JVM arguments when I started using Spring Boot 2.3 & BuildPacks in November 2020, got nowhere and gave up / put it to one side.

Two weeks ago I picked it up again and purely by chance found this: https://github.com/paketo-buildpacks/environment-variables

Basically, you prefix your environment variable with BPE_APPEND_ and this triggers the Environment Variables Build Pack to append your value to the environment variable.

NB: JAVA_TOOL_OPTIONS is what you want here, not JAVA_OPTS.

I needed to attach a Java Agent to monitor our microservices and something like this build.gradle snippet was what worked:

bootBuildImage {
  environment = [
    'BPE_DELIM_JAVA_TOOL_OPTIONS' : ' ',
    'BPE_APPEND_JAVA_TOOL_OPTIONS' : '-javaagent:my-java-agent.jar'
    ]
}

I used BPE_DELIM_JAVA_TOOL_OPTIONS to make sure a space was added to the existing value of JAVA_TOOL_OPTIONS before my value was appended (the buildpack also allows you to override or prepend to existing value - see their README).

PS: my value was more like '-javaagent:my-java-agent-${some-dynamic-version}.jar', so I needed double quotes, but that made it a Gradle String which didn't work so I had to write this instead "-javaagent:my-java-agent-${some-dynamic-version}.jar".toString().