Skill: docker

What I do

I provide expertise in containerisation using Docker. I focus on creating reproducible development environments, building optimised production images, and orchestrating multi-service applications.

When to use me

• Building production-ready container images
• Optimising build times and image sizes
• Defining multi-service stacks with Docker Compose
• Implementing multi-stage builds for compiled languages
• Ensuring consistent environments across dev, test, and prod

Core principles

1. Reproducibility — Environments should be identical regardless of the host
2. Immutability — Images are never modified once built; they are replaced
3. Layer Optimisation — Order commands to maximise cache hits
4. Security — Use minimal base images and run as non-root users
5. Isolation — Each container should have a single responsibility

Patterns & examples

Optimised Multi-stage Build:

# Stage 1: Build
FROM golang:1.21-alpine AS builder
WORKDIR /src
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN go build -o /app/bin/server

# Stage 2: Runtime (Minimal)
FROM alpine:3.18
RUN adduser -D -u 1000 appuser
USER appuser
COPY --from=builder /app/bin/server /server
ENTRYPOINT ["/server"]

Layer Caching (Correct Order):

FROM node:20-slim
WORKDIR /app
# Install dependencies first (infrequent changes)
COPY package.json package-lock.json ./
RUN npm ci
# Copy source code last (frequent changes)
COPY . .
CMD ["npm", "start"]

Anti-patterns to avoid

• ❌ Running as root — Increases attack surface; always use a non-privileged user
• ❌ Bloated base images — Avoid ubuntu or full node images; use alpine or slim
• ❌ Secrets in Dockerfile — Never use ENV or ARG for passwords or API keys
• ❌ Hardcoded Config — Use environment variables or volume mounts instead
• ❌ Large Layers — Don't combine unrelated files; keep .dockerignore updated

KB Reference

~/vaults/baphled/3. Resources/Knowledge Base/AI Development System/Skills/DevOps-Operations/Docker.md

Related skills

• devops - Broader operational patterns
• infrastructure-as-code - Provisioning container hosts
• automation - CI/CD integration for container builds
• security - Scanning images for vulnerabilities