Ops Docker

Docker Containerization (pointer)

Dockerfile syntax, Compose schema and image-publish flows drift on each release and are canonical at:

• Docker official — docs.docker.com (Engine + Compose + Buildx)
• Dockerfile best practices — docs.docker.com/develop/develop-images/dockerfile_best-practices
• Snyk Container Security — snyk.io/learn/container-security (vulnerability scanning, base-image hardening)
• Hadolint — github.com/hadolint/hadolint (Dockerfile linter, CI-integrable)
• Dive — github.com/wagoodman/dive (image layer analysis)

Foundation discipline (keep across releases)

• Multi-stage builds: always separate build deps from runtime image. The "node:20 with full npm" image weighs 1GB+; the runtime layer should be ~100MB. Build stage produces artifacts, runtime stage copies them in.
• Non-root user: RUN addgroup -S app && adduser -S app -G app && USER app — never run app code as root inside the container, even if "it's just a sandbox".
• .dockerignore mandatory: forgotten .git/ or node_modules/ in the build context bloats images by hundreds of MB and leaks secrets. The .dockerignore rules mirror your .gitignore plus build artifacts.
• HEALTHCHECK at the Dockerfile level: not just at the orchestrator level. Lets Docker/Compose detect unhealthy containers before the orchestrator does.
• Pin base image major+minor (node:20-alpine, not node:latest or bare node:20): floating tags break reproducibility; SHA pinning is overkill for most apps but worth it for security-critical builds.
• Secret management: never COPY .env or hardcode credentials in ENV. Use BuildKit secrets (--mount=type=secret) or runtime-injected env vars from the orchestrator.

See also

• /ops:ops-deploy — deployment checklist consumes the built image
• /ops:ops-database — Compose patterns for DB services (depends_on: { condition: service_healthy })
• qa-security — image scanning gate (Snyk/Trivy) before push
• ops-ci — Hadolint + image scan as CI steps