java-docker

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Containerize Java applications - Dockerfile optimization, JVM settings, security

⭐1stars🔀0forks📁View on GitHub🕐Updated Dec 31, 2025
[Cloud Infrastructure]

When & Why to Use This Skill

This Claude skill automates the creation of high-performance, production-ready Docker containers for Java applications. It solves common deployment challenges by optimizing Dockerfile layers for faster builds, fine-tuning JVM settings for container resource constraints to prevent OOM errors, and implementing industry-standard security hardening such as non-root execution and distroless images.

Use Cases

  • Optimizing build performance: Implementing multi-stage builds and layer caching strategies to significantly reduce Docker image size and CI/CD pipeline duration.
  • JVM Resource Management: Automatically configuring MaxRAMPercentage and container support flags to ensure Java applications respect Kubernetes memory limits and avoid OOMKilled events.
  • Security Hardening: Migrating legacy root-based containers to secure non-root users and utilizing distroless or Alpine base images to minimize the attack surface.
  • Spring Boot Deployment: Generating specialized Dockerfiles that leverage Spring Boot's layered JAR feature for efficient dependency management and faster updates.
  • Troubleshooting Containerized Java: Diagnosing and resolving issues related to heap memory visibility, permission denials in read-only filesystems, and health check failures.
namejava-docker
descriptionJava version
sasmp_version"1.3.0"
version"3.0.0"
bonded_agent08-java-devops
bond_typePRIMARY_BOND
allowed-toolsRead, Write, Bash, Glob, Grep
typestring
enum[temurin, distroless, alpine]
default"21"

Java Docker Skill

Containerize Java applications with optimized Dockerfiles and JVM settings.

Overview

This skill covers Docker best practices for Java including multi-stage builds, JVM container settings, security hardening, and layer optimization.

When to Use This Skill

Use when you need to:

  • Create optimized Java Dockerfiles
  • Configure JVM for containers
  • Implement security best practices
  • Reduce image size
  • Set up health checks

Topics Covered

Dockerfile Optimization

  • Multi-stage builds
  • Layer caching strategy
  • Spring Boot layered JARs
  • Dependency caching

JVM Container Settings

  • UseContainerSupport
  • MaxRAMPercentage
  • GC selection
  • Exit on OOM

Security

  • Non-root users
  • Read-only filesystem
  • Vulnerability scanning
  • Secrets handling

Quick Reference

# Multi-stage optimized Dockerfile
FROM eclipse-temurin:21-jdk-alpine AS builder

WORKDIR /app

# Cache dependencies
COPY pom.xml .
COPY .mvn .mvn
RUN mvn dependency:go-offline -B

# Build and extract layers
COPY src ./src
RUN mvn package -DskipTests && \
    java -Djarmode=layertools -jar target/*.jar extract

# Runtime stage
FROM eclipse-temurin:21-jre-alpine

# Security: non-root user
RUN addgroup -S app && adduser -S app -G app
USER app

WORKDIR /app

# Copy layers in order of change frequency
COPY --from=builder /app/dependencies/ ./
COPY --from=builder /app/spring-boot-loader/ ./
COPY --from=builder /app/snapshot-dependencies/ ./
COPY --from=builder /app/application/ ./

# JVM container settings
ENV JAVA_OPTS="-XX:+UseContainerSupport \
    -XX:MaxRAMPercentage=75.0 \
    -XX:+ExitOnOutOfMemoryError \
    -XX:+UseG1GC"

EXPOSE 8080

HEALTHCHECK --interval=30s --timeout=3s --start-period=30s \
    CMD wget -qO- http://localhost:8080/actuator/health/liveness || exit 1

ENTRYPOINT ["sh", "-c", "java $JAVA_OPTS org.springframework.boot.loader.launch.JarLauncher"]

JVM Container Flags

# Recommended production settings
JAVA_OPTS="
  -XX:+UseContainerSupport
  -XX:MaxRAMPercentage=75.0
  -XX:InitialRAMPercentage=50.0
  -XX:+ExitOnOutOfMemoryError
  -XX:+HeapDumpOnOutOfMemoryError
  -XX:HeapDumpPath=/tmp/heapdump.hprof
  -XX:+UseG1GC
  -Djava.security.egd=file:/dev/./urandom
"

Base Image Comparison

Image Size Security Use Case
temurin:21-jre ~200MB Good General use
temurin:21-jre-alpine ~100MB Good Size-optimized
distroless/java21 ~80MB Best Production

Security Best Practices

# Non-root user
RUN addgroup -S app && adduser -S app -G app
USER app

# Read-only filesystem
# (Configure at runtime with --read-only)

# No shell access with distroless
FROM gcr.io/distroless/java21-debian12

# Health check
HEALTHCHECK --interval=30s --timeout=3s \
    CMD wget -qO- localhost:8080/actuator/health || exit 1

Troubleshooting

Common Issues

Problem Cause Solution
OOMKilled Heap > limit Set MaxRAMPercentage
Slow startup Large image Multi-stage build
Permission denied Root required Fix file permissions
No memory info Old JVM Update to Java 11+

Debug Checklist

□ Check container memory limits
□ Verify JVM sees container limits
□ Review health check configuration
□ Scan image for vulnerabilities
□ Test with resource constraints

Usage

Skill("java-docker")
  • java-maven-gradle - Build integration
  • java-microservices - K8s deployment