Package jmx prometheus exporter to be run as a Java Agent

[sidps]

This is part of addressing Yolean/kubernetes-kafka#322 (comment)

This solution involves building the javaagent jar and stashing it in a separate docker image, and may be built with docker build --target javaagent.

The image that's used for the exporter sidecar can be built with docker build --target httpserver.

[sidps]

I've tested that this works with docker-compose, by copying over the jar and sample config into the kafka container. The docker-compose.yaml looks something like this:

---
version: "3.7"
services:
  jmx-jar-init:
    image: <image-we-just-built>
    entrypoint:
      - /bin/bash
      - -c
      - |
        cp jmx_prometheus_javaagent.jar /jmx-jar/;
        cp example_configs/kafka-2_0_0.yml /jmx-jar/
    volumes:
      - type: volume
        source: jmx-jar
        target: /jmx-jar
  kafka:
    image: solsson/kafka:2.3.0@sha256:b59603a8c0645f792fb54e9571500e975206352a021d6a116b110945ca6c3a1d
    entrypoint:
      - /bin/bash
      - -c
      - |
        until test -f "/jmx-jar/jmx_prometheus_javaagent.jar"; do
          sleep 3;
        done;
        until test -f "/jmx-jar/kafka-2_0_0.yml"; do
          sleep 3;
        done;
        ./bin/kafka-server-start.sh /etc/kafka/server.properties
    environment:
      - EXTRA_ARGS=-javaagent:/jmx-jar/jmx_prometheus_javaagent.jar=8080:/jmx-jar/kafka-2_0_0.yml
    volumes:
      - type: volume
        source: jmx-jar
        target: /jmx-jar
    network_mode: host
    depends_on:
      - zookeeper
      - jmx-jar-init
  zookeeper:
    image: solsson/kafka:2.3.0@sha256:b59603a8c0645f792fb54e9571500e975206352a021d6a116b110945ca6c3a1d
    network_mode: host
    entrypoint:
      - ./bin/zookeeper-server-start.sh
      - /etc/kafka/zookeeper.properties

volumes:
  jmx-jar:

And then metrics were exposed at localhost:8080

[sidps]

This would imply a mutation on the tag for the existing jmx exporter image, because a new layer has been introduced.

Would it make sense to bump the version? We're currently pointing at 0.12 of the jmx exporter, while 0.13 has been released.

[sidps]

This isn't exactly a diff, just copy-pasta from above with the appropriate selection in find.