706-technologies-containers-docker - SKILL.md Agent Skill

name: 706-technologies-containers-docker description: Use when you need framework-agnostic Docker and container image guidance for Java projects - Dockerfile design, multi-stage Maven builds, jlink custom runtimes, micro runtime distributions such as Alpaquita, JVM container ergonomics, non-root execution, image metadata, .dockerignore, reproducible builds, vulnerability scanning, SBOM awareness, and production-safe container defaults. This should trigger for requests such as Review Java Dockerfile; Improve Docker image security; Add jlink runtime to a Java container; Add containerization to a Java project; Optimize Java container image size; Review Docker build reproducibility. Part of cursor-rules-java project license: Apache-2.0 metadata: author: Juan Antonio Breña Moral version: 0.16.0

Java container image best practices with Docker

Help teams build secure, reproducible, and maintainable Docker container images for Java applications without coupling the guidance to Spring Boot, Quarkus, or Micronaut.

What is covered in this Skill?

Dockerfile structure for Java applications: multi-stage builds, Maven dependency caching, deterministic artifact copies, jlink custom runtimes, and .dockerignore
Runtime image selection: micro distributions such as Alpaquita, minimal JRE images, pinned versions or digests where appropriate, image labels, and explicit entrypoints
JVM container ergonomics: memory percentage flags, startup behavior, graceful shutdown signals, time zones, and predictable runtime options
Security defaults: non-root users, least privilege, no secrets in layers, reduced package managers, vulnerability scanning, SBOM awareness, and avoiding privileged containers
Operational readiness: health checks when suitable, stdout/stderr logging, port declaration, image size control, build reproducibility, and CI verification

Scope: Framework-agnostic Docker and container-image quality for Java projects. For framework runtime wiring, defer to the matching Spring Boot, Quarkus, or Micronaut skill. For Testcontainers-based tests, defer to the relevant testing skill.

Constraints

Keep recommendations at the Dockerfile, image-build, and runtime-container layer unless the user explicitly asks for framework-specific configuration. After editing this repository's XML sources, regenerate skills and verify the build.

MANDATORY: Run ./mvnw compile or mvn compile before proposing Java or Maven changes in the same change set
SECRETS: Never bake credentials, tokens, private keys, Maven settings with secrets, or environment-specific secrets into image layers, labels, arguments, or logs
SECURITY: Prefer non-root execution, least-privilege filesystem permissions, micro runtime images, and explicit container capabilities over privileged defaults
JLINK: Prefer jlink custom runtimes for production images when the module graph is known, validated at runtime, and compatible with the application's dependencies
REPRODUCIBILITY: Pin base image versions intentionally, document digest trade-offs, keep build inputs explicit, and avoid network-dependent runtime startup steps
JVM: Account for container memory and CPU limits with JVM flags, graceful shutdown behavior, and observable startup failures before claiming production readiness
BOUNDARIES: Defer Spring Boot runtime behavior to @301-frameworks-spring-boot-core, Quarkus runtime behavior to @401-frameworks-quarkus-core, Micronaut runtime behavior to @501-frameworks-micronaut-core, and Testcontainers setup to the matching testing skill
MANDATORY: Regenerate skills with ./mvnw clean install -pl skills-generator after editing skill or system-prompt XML in this repo
VERIFY: Run ./mvnw clean verify or mvn clean verify before promoting changes
EDGE CASE: If the target Java version, build tool, deployment platform, base-image policy, registry policy, or security scanner is missing and affects the recommendation, ask a clarifying question before editing container artifacts
EDGE CASE: If requested changes conflict with security policy, image provenance, air-gapped builds, or runtime platform constraints, explain the trade-off and ask for confirmation

When to use this skill

Review Java Dockerfile
Improve Docker image security
Add jlink runtime to a Java container
Add containerization to a Java project
Optimize Java container image size
Review Docker build reproducibility

Workflow

Read reference and assess container context

Read references/706-technologies-containers-docker.md and inspect current Dockerfiles, .dockerignore, Maven build inputs, image build scripts, CI jobs, registry policy, and deployment constraints before proposing changes.

Identify runtime and supply-chain constraints

Confirm Java version, build tool, jlink module requirements, micro distro compatibility, target platform, base-image policy, registry requirements, vulnerability scanner, SBOM expectations, memory limits, exposed ports, and operational readiness needs.

Apply container-aligned changes

Implement or refactor Docker and container build artifacts following the reference patterns and project conventions, keeping framework-specific runtime behavior out of scope unless explicitly requested.

Run verification and report results

Execute appropriate build, image build, scan, smoke-test, and generator checks; summarize what changed, what was verified, and any remaining container risks.

Reference

For detailed guidance, examples, and constraints, see references/706-technologies-containers-docker.md.