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Docker Cheat Sheet

A Docker cheat sheet can be a handy reference while learning and working with Docker. Here's a comprehensive Docker cheat sheet covering the basic commands and concepts:

Images and Containers​

  • docker pull [image_name:tag]: Pull an image from Docker Hub.
  • docker build -t [image_name:tag][path_to_Dockerfile]: Build an image from a Dockerfile.
  • docker images: List all available images.
  • docker rmi [image_id]: Remove an image.
  • docker run [options][image_name:tag]: Run a container from an image.
    • -d: Run in detached mode (in the background).
    • -p [host_port]:[container_port]: Map ports between host and container.
    • --name [container_name]: Specify a name for the container.
    • -e [env_variable=value]: Set environment variables.
    • -v [host_path]:[container_path]: Mount volumes between host and container.
    • --rm: Remove the container when it stops.
  • docker ps: List running containers.
    • -a: List all containers (including stopped ones).
  • docker stop [container_name/ID]: Stop a running container.
  • docker start [container_name/ID]: Start a stopped container.
  • docker restart [container_name/ID]: Restart a container.

Docker Compose​

  • docker-compose up: Create and start containers defined in the docker-compose.yml file.
    • -d: Run in detached mode.
  • docker-compose down: Stop and remove containers defined in the docker-compose.yml file.
  • docker-compose logs [container_name]: View logs of a specific container.
  • docker-compose exec [container_name][command]: Execute a command in a running container.

Docker Volumes​

  • docker volume create [volume_name]: Create a named volume.
  • docker volume ls: List all volumes.
  • docker volume inspect [volume_name]: Display detailed information about a volume.
  • docker run -v [volume_name]:[container_path]: Mount a volume to a container.

Networking​

  • docker network create [network_name]: Create a custom network.
  • docker network ls: List all networks.
  • docker network inspect [network_name]: Display detailed information about a network.
  • docker run --network [network_name][image_name:tag]: Run a container in a specific network.

Other Commands​

  • docker ps -aq: List IDs of all containers (running and stopped).
  • docker rm [container_name/ID]: Remove a stopped container.
  • docker system prune: Remove all stopped containers, unused networks, and dangling images.

As you get more comfortable, you can delve into more advanced topics such as Dockerfile best practices, multi-stage builds, Docker Swarm for orchestration, and Kubernetes for container management.


Multi-Stage Builds​

Multi-stage builds are a Docker feature that allows you to create smaller, more efficient Docker images by using multiple build stages within a single Dockerfile. Each build stage can have its own base image and set of instructions, and only the necessary artifacts are carried forward to the next stage.

Benefits

  • Smaller Images: Unnecessary build dependencies and intermediate files are discarded, resulting in smaller final images.
  • Improved Security: Only the necessary components are included, reducing potential attack vectors.
  • Simpler Build Process: Developers can bundle various steps (compilation, testing, etc.) into a single Dockerfile.
  • Faster Builds: The build process can be more efficient due to fewer layers and smaller context.

Example

# Stage 1: Build application
FROM node:14 AS build
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

# Stage 2: Production image
FROM nginx:alpine
COPY --from=build /app/dist /usr/share/nginx/html
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

In this example, the first stage builds the application using Node.js, while the second stage uses a minimal Nginx image to serve the built files. The --from=build instruction copies files from the first stage into the second stage without carrying over unnecessary build artifacts.


Docker Swarm​

Docker Swarm is a native orchestration and clustering solution for Docker. It allows you to create and manage a cluster of Docker nodes, turning them into a single virtual Docker engine. Docker Swarm enables you to deploy and manage containers across multiple nodes, providing high availability and scalability.

Key Concepts

  • Node: A physical or virtual machine in the Docker Swarm cluster.
  • Service: A definition of a desired state for a containerized application, specifying which image to use, how many replicas to run, and more.
  • Task: An instance of a service running on a node.
  • Stack: A collection of services that make up an application, defined using a Compose file.
  • Manager Node: Controls the swarm and maintains the desired state.
  • Worker Node: Executes tasks assigned by the manager nodes.

Benefits

  • High Availability: Services can be replicated across multiple nodes for fault tolerance.
  • Scalability: Easily scale services up or down to meet demand.
  • Service Discovery: Built-in DNS for service discovery among containers.
  • Load Balancing: Traffic to services is automatically load balanced.
  • Rolling Updates: Services can be updated with minimal downtime.
  • Secrets Management: Securely manage sensitive data like passwords and tokens.

Getting Started

  • Initialize a Swarm: Use the docker swarm init command on a manager node.
  • Deploy Services: Define and deploy services using the docker service create command.
  • Scaling: Scale services up or down using the docker service scale command.
  • Load Balancing: Access services through the swarm's load balancer.
# Initialize Swarm on manager node
docker swarm init

# Deploy a service
docker service create --name web --replicas 3 -p 80:80 nginx:alpine

# Scale the service
docker service scale web=5

In this example, the nginx service is deployed with three replicas. It can be scaled to five replicas for higher availability and load distribution.

Docker Swarm provides a simpler and more lightweight alternative to more complex orchestration solutions like Kubernetes, making it a great choice for many use cases.


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