Cookbook: Container and Sidecar Deployment

Situation: You want to record GC data inside a Docker container with minimal footprint and pull the .cjfr files out for offline analysis; without the container needing cjfr inflate capability.

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Build the base image with the inflaterless agent

FROM eclipse-temurin:21-jre

# ~1.5 MB agent JAR; no inflate, no JMC dependencies
ADD https://github.com/parttimenerd/condensed-data/releases/latest/download/condensed-data-linux-amd64-inflaterless.jar \
    /opt/cjfr/cjfr-agent.jar

# Mount point for recordings
RUN mkdir -p /var/rec
VOLUME /var/rec

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Start with rotating recording

ENV JAVA_TOOL_OPTIONS="-javaagent:/opt/cjfr/cjfr-agent.jar=start,/var/rec/app_\$index.cjfr,rotating,max-files=5,max-size=100m"

Or pass it at docker run time:

docker run \
  -v /host/recordings:/var/rec \
  -e JAVA_TOOL_OPTIONS="-javaagent:/opt/cjfr/cjfr-agent.jar=start,/var/rec/app_\$index.cjfr,rotating,max-files=5,max-size=100m" \
  myapp:latest

Escape $index

docker run -e "…" (shell string): the shell expands $index to empty before Docker sees it. Use \$index in double-quoted strings.

Dockerfile ENV line: Docker performs its own variable substitution on ENV values using declared ARG/ENV. Use \$index to pass the literal placeholder through to the JVM.

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Pull recordings and analyse on the host

The container only needs the inflaterless JAR. Inflation uses the full JAR on your workstation:

# Copy from container
docker cp mycontainer:/var/rec/. ./recordings/

# Summary; no inflate needed
cjfr summary recordings/app_0.cjfr recordings/app_1.cjfr

# Inflate the interesting window
cjfr inflate --start="2024-05-24 14:00:00" --duration=1h \
  recordings/app_0.cjfr recordings/app_1.cjfr \
  recordings/incident.jfr

---

For absolute minimum JAR size (~450 KB)

Use the minimal variant; LZ4FRAMED and GZIP, ProGuard-optimised:

condensed-data-linux-amd64-inflaterless-minimal.jar

The recording format is identical; any full JAR can inflate it.

---

Kubernetes: volume-mount + init container pattern

volumes:
  - name: gc-recordings
    emptyDir: {}
initContainers:
  - name: cjfr-agent
    image: curlimages/curl
    command:
      - sh
      - -c
      - |
        curl -L -o /agent/cjfr-agent.jar \
          https://github.com/parttimenerd/condensed-data/releases/latest/download/condensed-data-linux-amd64-inflaterless.jar
    volumeMounts:
      - name: gc-recordings
        mountPath: /agent
containers:
  - name: myapp
    env:
      - name: JAVA_TOOL_OPTIONS
        # Kubernetes env values are not shell-expanded; $index reaches the JVM literally
        value: "-javaagent:/agent/cjfr-agent.jar=start,/var/rec/app_$index.cjfr,rotating,max-files=10,max-size=100m"
    volumeMounts:
      - name: gc-recordings
        mountPath: /var/rec