container-ops

What I do

• •Guide Containerfile/Dockerfile authoring with best practices
• •Provide patterns for multi-stage builds
• •Document Podman-specific features and differences from Docker
• •Cover image security and scanning practices

When to use me

Use this skill when building container images, troubleshooting container issues, or setting up containerized development environments.

Podman vs Docker

Podman is a drop-in replacement for Docker with key differences:

Containerfile Best Practices

Multi-stage builds

# Stage 1: Build
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --production=false
COPY . .
RUN npm run build

# Stage 2: Runtime
FROM node:20-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
USER node
CMD ["node", "dist/index.js"]

Layer optimization

1. •Order instructions from least to most frequently changing
2. •Combine RUN commands to reduce layers
3. •Use .containerignore / .dockerignore to exclude unnecessary files
4. •Pin base image versions (avoid latest tag)

Security

1. •Use non-root user: USER node or USER 1000
2. •Use COPY instead of ADD (unless extracting archives)
3. •Scan images: podman image scan <image>
4. •Use minimal base images (-alpine, -slim, distroless)
5. •Do not store secrets in images -- use runtime env vars or mounted secrets

Common Podman Commands

# Build
podman build -t myapp:latest .

# Run (detached, with port mapping)
podman run -d --name myapp -p 8080:3000 myapp:latest

# View logs
podman logs -f myapp

# Execute command in running container
podman exec -it myapp sh

# Stop and remove
podman stop myapp && podman rm myapp

# List images and containers
podman images
podman ps -a

# Prune unused resources
podman system prune -a

Podman Pods

Pods group containers that share network and IPC namespaces (similar to Kubernetes pods):

# Create a pod
podman pod create --name mystack -p 8080:80

# Add containers to the pod
podman run -d --pod mystack --name web nginx
podman run -d --pod mystack --name api myapi:latest

# Manage the pod
podman pod ps
podman pod stop mystack
podman pod rm mystack

Troubleshooting

Agent Integration

• •Build, run, and manage containers using Podman (not Docker).
• •Container build files live in cicd/, not at the project root.
• •NEVER delete containers, images, or volumes without user confirmation.
• •ALWAYS show what will change before executing destructive container operations.