docker-development

# Docker Development Patterns for building, testing, and deploying Docker containers. ## Core Principles 1. **Minimal** -- Alpine/distroless, multi-stage 2. **Secure** -- Non-root USER, no layer secrets, pin versions 3. **Testable** -- CI-verifiable: entrypoint bypass, DNS mocking 4. **Cache-efficient** -- deps first, clean in same layer ## Quick Reference ### Multi-Stage Build (Node.js) ```dockerfile FROM node:20-alpine AS builder WORKDIR /app COPY package*.json ./ RUN npm ci --only=production COPY . . FROM node:20-alpine RUN addgroup -g 1001 app && adduser -u 1001 -G app -D app USER app COPY --from=builder /app . HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \ CMD wget -qO- http://localhost:3000/health || exit 1 CMD ["node", "server.js"] ``` ### Multi-Stage Build (Go -- scratch/distroless) ```dockerfile FROM golang:1.22-alpine AS builder WORKDIR /app COPY go.* ./ RUN go mod download COPY . . RUN CGO_ENABLED=0 go build -o /app/server . FROM gcr.io/distroless/static:nonroot COPY --from=builder /app/server /server CMD ["/server"] ``` ### Layer Optimization ```dockerfile RUN apt-get update && \ apt-get install -y --no-install-recommends curl && \ rm -rf /var/lib/apt/lists/* ``` ### Build Cache: Copy Dependency Files First ```dockerfile COPY package*.json ./ RUN npm ci COPY . . ``` Manifests before source keeps install layers cached on source-only changes. ### BuildKit Secrets ```dockerfile RUN --mount=type=secret,id=ssh_key,dst=/root/.ssh/id_rsa git clone git@github.com:org/repo.git ``` `ENV`/`ARG`/`COPY` secrets persist in `docker history`. Use `--mount=type=secret`. ### Docker Bake (Multi-Platform) ```hcl target "app" { platforms = ["linux/amd64", "linux/arm64"] cache-from = ["type=gha"] cache-to = ["type=gha,mode=max"] } ``` ## Security Anti-Patterns | Anti-pattern | Fix | | ------------------------------ | -------------------------------------------- | | `FROM image:latest` | Pin version: `image:1.2.3-alpine` | | No `USER` directive | `adduser` + `USER appuser` | | `chmod 777` | Use specific permissions: `chmod 550` | | `privileged: true` in compose | Remove or use specific `cap_add` | | `volumes: [/:/host]` | Mount only needed paths | | `ports: ["0.0.0.0:3000:3000"]` | Bind to `127.0.0.1:3000:3000` | | `ENV DB_PASSWORD=secret` | Use `--mount=type=secret` or compose secrets | ## CI Testing Gotchas 1. **Bypass entrypoint**: `docker run --rm --entrypoint php myimage -v` 2. **Mock upstream DNS**: `docker run --rm --add-host backend:127.0.0.1 nginx-image nginx -t` 3. **Compose validation**: `cp .env.example .env` before `docker compose config` 4. **Secret scanning**: Exclude `.env.example`, README, docs from scanners 5. **Root-owned artifacts**: in-container installs leave root-owned bind-mount dirs (`EACCES` on host) -- `references/bind-mount-ownership.md` ## .dockerignore Exclude: `.git`, `node_modules`/`vendor`, `.env*`, `*.pem`, `*.key` ## Compose Essentials - startup ordering: `depends_on.condition: service_healthy` + `healthcheck` `start_period` - `networks.internal: true` isolates databases from external access - `profiles: [debug]`: services start only with `--profile debug` ## References - `references/ci-testing.md` -- CI testing patterns for Docker images - `references/dind-testing-patterns.md` -- Docker-in-Docker (DinD) testing patterns - `references/bind-mount-ownership.md` -- root-owned bind-mount artifacts