Docker Guide Index

A collection of Docker-related learning paths, command references, and patterns. Organized from beginner basics to production practices.

Core Concepts

Docker packages an application and its dependencies into a container — a lightweight, isolated environment that runs the same way on any host.

Essential Commands

# Build an image from a Dockerfile in current directory
docker build -t myapp:latest .

# Run a container (detached, port mapped)
docker run -d -p 8080:80 --name myapp myapp:latest

# List running containers
docker ps

# List all containers (including stopped)
docker ps -a

# View container logs (follow mode)
docker logs -f myapp

# Execute a command inside a running container
docker exec -it myapp /bin/sh

# Stop and remove a container
docker stop myapp && docker rm myapp

# Remove all stopped containers
docker container prune

Minimal Dockerfile Pattern

# Multi-stage build — builder stage
FROM golang:1.23-alpine AS builder
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN go build -o /bin/server ./cmd/server

# Final stage — minimal runtime image
FROM alpine:3.20
RUN adduser -D -u 1001 appuser
USER appuser
COPY --from=builder /bin/server /bin/server
EXPOSE 8080
CMD ["/bin/server"]

Multi-stage builds keep the final image lean — the Go toolchain stays in the builder stage; only the binary ships.

Docker Compose

# docker-compose.yml
version: "3.9"
services:
  app:
    build: .
    ports:
      - "8080:8080"
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/mydb
    depends_on:
      db:
        condition: service_healthy

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
      POSTGRES_DB: mydb
    volumes:
      - pgdata:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U user"]
      interval: 5s
      timeout: 5s
      retries: 5

volumes:
  pgdata:

Debugging Patterns

# Inspect container metadata (networking, mounts, env)
docker inspect myapp

# Check resource usage
docker stats myapp

# Copy files out of a container
docker cp myapp:/app/logs/error.log ./error.log

# Run a temporary container to debug the image
docker run --rm -it myapp:latest /bin/sh

# Check what changed from the base image
docker diff myapp

Best Practices

• Pin base image versions (alpine:3.20, not alpine:latest)
• Run as non-root user (USER appuser)
• Use .dockerignore to exclude node_modules, .git, build artifacts
• One process per container — use Compose for multi-service setups
• Use multi-stage builds to keep images small
• Never put secrets in ENV or build args — use runtime secrets or mounted files