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PublishedOctober 28, 2026 at 05:23 PM
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name: docker-management description: Build, optimize, and troubleshoot Docker containers and images. category: devops risk: critical source: https://github.com/BagelHole/DevOps-Security-Agent-Skills source_repo: BagelHole/DevOps-Security-Agent-Skills source_type: community date_added: '2026-09-20' license: MIT license_source: https://github.com/BagelHole/DevOps-Security-Agent-Skills/blob/main/LICENSE compatibility: Requires the relevant platform CLIs (kubectl, helm, terraform, git, CI runners) and authorized access to the target environment. Docs-only; helper scripts and templates not bundled. metadata: author: devops-skills version: '1.0'

Docker Management

Build, run, and manage Docker containers for application deployment and development.

When to Use This Skill

Use this skill when:

  • Creating and optimizing Dockerfiles
  • Building and tagging Docker images
  • Running and managing containers
  • Debugging container issues
  • Configuring Docker networking and volumes
  • Implementing container security best practices

Execution Scope

Confirm the selected Docker context and project before any operation. Build instructions execute contributed commands; inspect the Dockerfile, build context, scripts and downloaded dependencies first. Image publication, shared-container stops and volume deletion need authorization for the exact target. Do not expose environment values, image history or logs containing credentials. These examples are independent fragments with project-specific assets, not a complete deployment.

Prerequisites

  • Docker Engine installed (20.10+)
  • Basic command line knowledge
  • Understanding of application deployment

Dockerfile Best Practices

Multi-Stage Build

dockerfile
# Build stage
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build && npm prune --omit=dev
 
# Production stage
FROM node:20-alpine AS production
WORKDIR /app
RUN addgroup -g 1001 -S nodejs && \
    adduser -S nodejs -u 1001 -G nodejs
COPY --from=builder --chown=nodejs:nodejs /app/dist ./dist
COPY --from=builder --chown=nodejs:nodejs /app/node_modules ./node_modules
USER nodejs
EXPOSE 3000
CMD ["node", "dist/index.js"]

Layer Optimization

dockerfile
FROM python:3.12-slim
 
# Install dependencies first (cached unless requirements change)
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
 
# Copy application code (changes frequently)
COPY . .
 
CMD ["python", "app.py"]

Security Hardening

dockerfile
FROM node:20-alpine
 
# Create non-root user
RUN addgroup -g 1001 appgroup && \
    adduser -u 1001 -G appgroup -D appuser
 
WORKDIR /app
 
# Copy with proper ownership
COPY --chown=appuser:appgroup . .
 
# Drop privileges
USER appuser
 
# Use exec form for proper signal handling
CMD ["node", "server.js"]

Building Images

Basic Build

bash
# Build with tag
docker build -t myapp:1.0 .
 
# Build with build args
docker build --build-arg NODE_ENV=production -t myapp:prod .
 
# Build for specific platform
docker build --platform linux/amd64 -t myapp:amd64 .
 
# Build with no cache
docker build --no-cache -t myapp:fresh .

Multi-Platform Builds

bash
# Create builder
docker buildx create --name multiplatform --use
 
# Build for multiple architectures
docker buildx build \
  --platform linux/amd64,linux/arm64 \
  -t myregistry/myapp:latest \
  --push .

Running Containers

Basic Operations

bash
# Run container
docker run -d --name myapp -p 8080:3000 myapp:latest
 
# Run with environment variables
docker run -d \
  -e DATABASE_URL=postgres://localhost/db \
  -e NODE_ENV=production \
  myapp:latest
 
# Run with resource limits
docker run -d \
  --memory="512m" \
  --cpus="1.0" \
  myapp:latest
 
# Run with restart policy
docker run -d --restart=unless-stopped myapp:latest

Volume Management

bash
# Named volume
docker volume create mydata
docker run -v mydata:/app/data myapp:latest
 
# Bind mount
docker run -v "$(pwd)/config:/app/config:ro" myapp:latest
 
# tmpfs mount (memory)
docker run --tmpfs /tmp:rw,noexec,nosuid myapp:latest

Networking

bash
# Create network
docker network create mynetwork
 
# Run on network
docker run -d --network mynetwork --name api myapp:latest
 
# Connect existing container
docker network connect mynetwork existing-container
 
# Expose specific ports
docker run -d -p 127.0.0.1:8080:3000 myapp:latest

Container Lifecycle

Management Commands

bash
# List containers
docker ps -a
 
# Stop container
docker stop myapp
 
# Remove container
docker rm myapp
 
# Force remove running container
docker rm -f myapp
 
# Prune stopped containers
docker container prune -f

Logs and Monitoring

bash
# View logs
docker logs myapp
 
# Follow logs
docker logs -f --tail 100 myapp
 
# View resource usage
docker stats myapp
 
# Inspect container
docker inspect myapp

Debugging Containers

Interactive Access

bash
# Execute command in running container
docker exec -it myapp /bin/sh
 
# Run container with shell
docker run -it --rm myapp:latest /bin/sh
 
# Debug failed container
docker run -it --entrypoint /bin/sh myapp:latest

Troubleshooting

bash
# Check container logs for errors
docker logs myapp 2>&1 | grep -i error
 
# Inspect container state
docker inspect --format='{{.State.Status}}' myapp
 
# Check container processes
docker top myapp
 
# View container filesystem changes
docker diff myapp
 
# Export container filesystem
docker export myapp > myapp-fs.tar

Health Checks

dockerfile
HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
  CMD ["node", "-e", "fetch('http://localhost:3000/health').then(r=>process.exit(r.ok?0:1)).catch(()=>process.exit(1))"]
bash
# Check health status
docker inspect --format='{{.State.Health.Status}}' myapp

Image Management

Tagging and Pushing

bash
# Tag image
docker tag myapp:latest myregistry.com/myapp:v1.0
 
# Push to registry
docker push myregistry.com/myapp:v1.0
 
# Pull image
docker pull myregistry.com/myapp:v1.0

Cleanup

bash
# Remove unused images
docker image prune -a
 
# Destructive broad cleanup: only after explicit scope approval and verified backups
docker system prune -a --volumes
 
# Remove specific image
docker rmi myapp:old
 
# List image sizes
docker images --format "table {{.Repository}}\t{{.Tag}}\t{{.Size}}"

Image Analysis

bash
# View image history
docker history myapp:latest
 
# Inspect image layers
docker inspect myapp:latest
 
# Check image vulnerabilities (with Docker Scout)
docker scout cves myapp:latest

Docker Compose Integration

yaml
# docker-compose.yml
 
services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "127.0.0.1:3000:3000"
    environment:
      - NODE_ENV=production
    volumes:
      - app-data:/app/data
    depends_on:
      - db
    restart: unless-stopped
 
  db:
    image: postgres:15-alpine
    environment:
      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:?set a local fixture password}
    volumes:
      - db-data:/var/lib/postgresql/data
 
volumes:
  app-data:
  db-data:

Security Best Practices

Image Security

dockerfile
# Use specific version tags
FROM node:22-alpine
 
# Don't run as root
USER nobody
 
# Remove unnecessary packages
RUN apk del --purge .build-deps  # only if this virtual build-dependency group was created earlier
 
# Use COPY instead of ADD
COPY . .

Runtime Security

bash
# Run with security options
docker run -d \
  --security-opt=no-new-privileges \
  --cap-drop=ALL \
  --cap-add=NET_BIND_SERVICE \
  --read-only \
  myapp:latest
 
# Use user namespace remapping
# Add to /etc/docker/daemon.json: {"userns-remap": "default"}

Common Issues

Issue: Container Exits Immediately

Problem: Container starts and stops instantly Solution: Check if CMD/ENTRYPOINT runs foreground process, use docker logs to see errors

Issue: Cannot Connect to Container

Problem: Port not accessible Solution: Verify port mapping (-p), check container is running, verify firewall rules

Issue: Out of Disk Space

Problem: Docker using too much disk Solution: Inspect docker system df and named resources first. Remove only explicitly authorized unused targets; broad volume pruning can destroy data

Issue: Build Cache Not Working

Problem: Every build downloads dependencies Solution: Order Dockerfile instructions from least to most frequently changing

Best Practices

  • Use multi-stage builds to minimize image size
  • Never store secrets in images - use runtime injection
  • Pin base image versions for reproducibility
  • Implement health checks for production containers
  • Use .dockerignore to exclude unnecessary files
  • Run containers as non-root users
  • Scan images for vulnerabilities regularly
  • Use Docker BuildKit for faster builds

Related Skills

  • docker-compose (docker-compose) - Multi-container applications
  • container-scanning (container-scanning) - Security scanning
  • container-hardening (container-hardening) - Security hardening

Limitations

  • Guidance executes against real environments: confirm target, blast radius, and rollback plan before applying anything.
  • Never deploy to production without explicit approval. Docs-only import: upstream scripts and templates not bundled.

Example

bash
git status && git diff --stat
docker context show
docker compose config --quiet
Adapted from BagelHole/DevOps-Security-Agent-Skills (MIT); frontmatter, When to Use/Limitations, and safety boundaries added for upstream compliance. Docs-only import: helper scripts and templates not bundled.
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