Paketo Buildpack for OpenTelemetry not working with maven spring boot 2.5.12 app

I'm trying to add OpenTelemetry automated instrumentation to our spring boot app but I can't get it working.

The app is deployed as a docker image and the image is created via the spring-boot-maven-plugin.

I'm following these instructions: https://github.com/paketo-buildpacks/opentelemetry

I've added an env section to the spring-boot-maven-plugin config in the pom.xml:

        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <image>
                    <name>appname</name>
                    <env>
                        <BP_OPENTELEMETRY_ENABLED>true</BP_OPENTELEMETRY_ENABLED>
                    </env>
                </image>
            </configuration>
        </plugin>

I'm not sure this is the correct way to enable it but I'm having a hard time determining whether that step is working or not.

The docker image is created and run with:

    mvn clean spring-boot:build-image
    docker compose -f app.yml up

I've added environment variables to app.yml file (hostname replaced with XXXXXX):

    services:
      appname:
        image: appname:latest
        environment:
          - SPRING_PROFILES_ACTIVE=docker-local
          - BPE_OTEL_TRACES_EXPORTER=zipkin
          - BPE_OTEL_EXPORTER_ZIPKIN_ENDPOINT=http://XXXXXX:9411/api/v2/spans
          - BPE_OTEL_SERVICE_NAME=appname
          - BPE_OTEL_JAVAAGENT_ENABLED=true

I don't think these environment variables are being set, however because I don't see them when I run:

docker run --entrypoint launcher -it appname:latest bash -c set

I don't see any traces going to zipkin and I don't see anything in the logs.

Without docker, I have everything working fine.

I tried to figure out if I just need to use a more recent version of spring boot but I couldn't find a way to determine that.

I couldn't find any examples of apps that have this working.

Edit to include working solution:

Martin Theiss's solution is correct. Here is the section of the pom.xml that does everything:

        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <image>
                    <name>appname</name>
                    <buildpacks>
                        <buildpack>paketo-buildpacks/java</buildpack>
                        <buildpack>gcr.io/paketo-buildpacks/opentelemetry</buildpack>
                    </buildpacks>
                    <env>
                        <BP_OPENTELEMETRY_ENABLED>true</BP_OPENTELEMETRY_ENABLED>
                        <BPE_OTEL_JAVAAGENT_ENABLED>true</BPE_OTEL_JAVAAGENT_ENABLED>
                        <BPE_OTEL_TRACES_EXPORTER>zipkin</BPE_OTEL_TRACES_EXPORTER>
                        <BPE_OTEL_EXPORTER_ZIPKIN_ENDPOINT>http://zipkinhost:9411/api/v2/spans</BPE_OTEL_EXPORTER_ZIPKIN_ENDPOINT>
                        <BPE_OTEL_SERVICE_NAME>appname</BPE_OTEL_SERVICE_NAME>
                    </env>
                </image>
            </configuration>
        </plugin>

Note that this is sending traces directly to zipkin. Eventually I'll be sending traces to an opentelemetry collector.

Note also that I was wrong to try to put environment variables in the spring app.yml config file. These should be put in the pom.xml as per above.

OpenTelemetry buildpack is not contained in the buildpacks/java. You have to specify it additionally.

                    <image>
                        <buildpacks>
                            <buildpack>paketo-buildpacks/java</buildpack>
                            <buildpack>gcr.io/paketo-buildpacks/opentelemetry</buildpack>
                        </buildpacks>
                        <env>
                            <BP_OPENTELEMETRY_ENABLED>true</BP_OPENTELEMETRY_ENABLED>
                        </env>
                    </image>