Docker Basics:
- Docker Image: A lightweight, standalone, executable package that includes everything needed to run an application, including code, libraries, dependencies, and configurations.
- Docker Container: An instance of a Docker image that is running as a process on the host system.
- Dockerfile: A text file that contains instructions for building a Docker image.
- Docker Registry: A place to store and share Docker images, such as Docker Hub.
Docker Commands:
- docker run: Runs a Docker container from an image. Example: docker run hello-world
- docker build: Builds a Docker image from a Dockerfile. Example: docker build -t my-image .
- docker images: Lists all Docker images on the host system. Example: docker images
- docker ps: Lists all running Docker containers on the host system. Example: docker ps
- docker stop: Stops a running Docker container. Example: docker stop my-container
- docker rm: Removes a stopped Docker container. Example: docker rm my-container
- docker rmi: Removes a Docker image. Example: docker rmi my-image
- docker exec: Runs a command inside a running Docker container. Example: docker exec my-container ls
Dockerfile Instructions:
- FROM: Specifies the base image for the Docker image. Example: FROM ubuntu:latest
- RUN: Executes a command inside the Docker image during the build process. Example: RUN apt-get update && apt-get install -y python
- COPY: Copies files or directories from the host system to the Docker image. Example: COPY app.py /app/
- EXPOSE: Exposes a port for the Docker container. Example: EXPOSE 8000
- CMD: Specifies the default command to run when a Docker container is started. Example: CMD ["python", "app.py"]
Docker Compose
Docker Compose is a tool used to run multi-container Docker applications. It allows you to define and run multiple containers as a single application, providing an easy way to manage, configure, and deploy your containers
Docker Compose Basics
- Docker Compose: A tool for defining and running multi-container Docker applications.
- docker-compose.yml: A YAML file that defines the services, networks, and volumes for a Docker Compose application.
- Service: A containerized application that can be run as part of a Docker Compose application.
- Network: A named network that connects the services in a Docker Compose application.
- Volume: A named volume that can be used to share data between containers in a Docker Compose application.
Basic commands:
- docker-compose up - starts all the services defined in the docker-compose.yml file.
- docker-compose down - stops and removes all the containers, networks, and volumes created by docker-compose up.
- docker-compose build - builds or rebuilds the Docker images of the services defined in the docker-compose.yml file.
- docker-compose ps - lists all the running containers for the services defined in the docker-compose.yml file.
- docker-compose logs - shows the logs of the containers for the services defined in the docker-compose.yml file.
- docker-compose start - starts the containers for the services defined in the docker-compose.yml file.
- docker-compose stop - stops the containers for the services defined in the docker-compose.yml file.
- docker-compose restart - restarts the containers for the services defined in the docker-compose.yml file.
- docker-compose pause - pauses the containers for the services defined in the docker-compose.yml file.
- docker-compose unpause - unpauses the containers for the services defined in the docker-compose.yml file.
- docker-compose exec - runs a command inside a running container for a service defined in the docker-compose.yml file.
- docker-compose pull - pulls the latest images for the services defined in the docker-compose.yml file.
- docker-compose config - validates and displays the configuration of the services defined in the docker-compose.yml file.
- docker-compose kill - sends a SIGKILL signal to the containers for the services defined in the docker-compose.yml file.
- docker-compose rm - removes the stopped containers for the services defined in the docker-compose.yml file.
Configuration:
- docker-compose.yml: Default configuration file for Docker Compose.
- -f/--file flag: Specifies an alternate compose file.
- --project-name flag: Specifies an alternate project name.
Services:
- services: Defines a list of services to run in the application.
- build: Specifies the path to the Dockerfile for building an image.
- image: Specifies the name of the image to use.
- container_name: Specifies the name of the container.
- ports: Exposes ports on the host machine.
- volumes: Mounts directories or files from the host machine to the container.
- environment: Sets environment variables for the service.
Networks:
- networks: Defines a list of custom networks to create.
- driver: Specifies the network driver to use.
- name: Specifies the name of the network.
- external: Specifies an existing network to connect to.
Volumes:
- volumes: Defines a list of named volumes to create.
- driver: Specifies the volume driver to use.
- name: Specifies the name of the volume.
- external: Specifies an existing volume to use.
Docker Compose Service Configuration
A Docker Compose service can be configured with the following options:
- build: Specifies the path to the Dockerfile used to build the service image.
- image: Specifies the name of the Docker image to use for the service.
- ports: Specifies the port mapping between the host system and the container.
- environment: Specifies environment variables to be set in the container.
- networks: Specifies the networks to connect the container to.
- volumes: Specifies the volumes to mount in the container.
Docker Compose File Structure
A Docker Compose file consists of the following sections:
- version: The version of the Docker Compose file format to use.Example: version: '3'
- services: The services to run as part of the Docker Compose application.Example:
services:
? app:
? ? build: .
? ? ports:
? ? ? - "8000:8000"
? ? environment:
? ? ? DEBUG: "true"
- networks: The networks to create and connect the services in the Docker Compose application.Example:
networks:
? app-network:
? ? driver: bridge
- volumes: The volumes to create and share between the containers in the Docker Compose application.Example:
volumes:
? data:
? ? driver: local
Examples:
Example 1: Simple web application
version: '3'
services:
? web:
? ? build: .
? ? ports:
? ? ? - "5000:5000"
This configuration defines a single service named "web" that builds an image from the Dockerfile in the current directory and exposes port 5000 on the host machine.
Example 2: Multi-container application with custom network and volumes
version: '3'
services:
? web:
? ? build: .
? ? ports:
? ? ? - "5000:5000"
? ? volumes:
? ? ? - type: bind
? ? ? ? source: ./app
? ? ? ? target: /app
? ? networks:
? ? ? - mynet
? db:
? ? image: postgres
? ? volumes:
? ? ? - db_data:/var/lib/postgresql/data
? ? networks:
? ? ? - mynet
networks:
? mynet:
volumes:
? db_data:
This configuration defines two services named "web" and "db" that use a custom network named "mynet" and a named volume named "db_data". The "web" service builds an image from the Dockerfile in the current directory, exposes port 5000 on the host machine, mounts the ./app directory as a volume in the container, and connects to the "mynet" network. The "db" service uses the "postgres" image, mounts the "db_data" volume, and connects to the "mynet" network.
