Docker Cheat Sheet for DevOps Engineers

Docker Basics

Docker is an open-source platform that automates the deployment of applications inside lightweight containers, ensuring consistency across multiple development and release cycles.

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Docker Commands

Docker Installation

# Install Docker on Ubuntu
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io

Basic Commands

# Check Docker version
docker --version

# Pull an image from Docker Hub
docker pull <image_name>

# List all Docker images
docker images

# Run a container from an image
docker run -it <image_name> /bin/bash

# List running containers
docker ps

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

# Stop a running container
docker stop <container_id>

# Remove a container
docker rm <container_id>

# Remove an image
docker rmi <image_name>

Real-Life Example

# Pull and run a simple web server
docker pull nginx
docker run -d -p 8080:80 nginx

Access the Nginx web server on your browser at http://localhost:8080.

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Docker Compose

Docker Compose is a tool for defining and running multi-container Docker applications.

Compose File Example

version: '3'
services:
  web:
    image: nginx
    ports:
      - "8080:80"
  db:
    image: postgres
    environment:
      POSTGRES_PASSWORD: example

Docker Compose Commands

# Start services defined in the Compose file
docker-compose up

# Start services in detached mode
docker-compose up -d

# Stop services
docker-compose down

# View service logs
docker-compose logs

Real-Life Example

Create a docker-compose.yml file with the content above, then run:

docker-compose up

This will start both an Nginx web server and a PostgreSQL database.

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Docker Networking

Docker networking allows containers to communicate with each other, either on the same host or across different hosts.

Basic Networking Commands

# List networks
docker network ls

# Create a network
docker network create <network_name>

# Connect a container to a network
docker network connect <network_name> <container_name>

# Disconnect a container from a network
docker network disconnect <network_name> <container_name>

Real-Life Example

# Create a network
docker network create my_network

# Run two containers in the same network
docker run -d --name web --network my_network nginx
docker run -d --name db --network my_network postgres

# Connect to the web container and ping the db container
docker exec -it web /bin/bash
ping db

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Docker Images

A Docker image is a read-only template with instructions for creating a Docker container.

Managing Images

# Build an image from a Dockerfile
docker build -t <image_name> .

# Tag an image
docker tag <image_id> <repository>/<image_name>:<tag>

# Push an image to a repository
docker push <repository>/<image_name>:<tag>

# Remove an image
docker rmi <image_name>

Real-Life Example

Create a Dockerfile with the following content:

FROM ubuntu:latest
RUN apt-get update && apt-get install -y nginx
CMD ["nginx", "-g", "daemon off;"]

Build and run the image:

docker build -t my_nginx_image .
docker run -d -p 8080:80 my_nginx_image

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Docker Containers

A Docker container is a runnable instance of an image. You can create, start, stop, move, or delete a container using Docker commands.

Basic Container Commands

# Run a container
docker run -d --name <container_name> <image_name>

# Start a stopped container
docker start <container_id>

# Stop a running container
docker stop <container_id>

# Restart a container
docker restart <container_id>

# View container logs
docker logs <container_id>

# Execute a command in a running container
docker exec -it <container_id> <command>

Real-Life Example

# Run a detached Nginx container
docker run -d --name my_nginx -p 8080:80 nginx

# View logs of the Nginx container
docker logs my_nginx

# Execute a bash shell inside the Nginx container
docker exec -it my_nginx /bin/bash

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Conclusion

Docker simplifies the deployment process by encapsulating applications in containers, providing consistency across different environments. By leveraging Docker Compose, you can easily manage multi-container applications. Docker networking ensures seamless communication between containers, while Docker images and containers allow for efficient application management and scaling.

With this cheat sheet, you should have a foundational understanding of Docker and its core components, enabling you to streamline your DevOps workflows effectively.

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