Docker Fundamentals

This repository contains notes and practical examples for learning the fundamentals of Docker. It covers basic commands for working with images and containers, essential instructions for building images with a Dockerfile, and the core concepts of Docker volumes, networks, and Compose.

The examples are intended for local practice with the Dockerfile, the docker-compose.yml file, and the web content available in the html/ directory.

Contents

• Docker and basic commands
• Dockerfile instructions
• Docker volumes
• Docker networks
• Docker Compose

Docker and Basic Commands

Command	Description	Example
docker --version	Check Docker version	docker --version
docker pull <image_name>	Download an image	docker pull python:3.8
docker images	List downloaded images	docker images
docker run <image_name>	Run a container	docker run -d -p 8080:80 nginx
docker ps	List running containers	docker ps
docker ps -a	List all containers (running and stopped)	docker ps -a
docker stop <container_id>	Stop a running container	docker stop 1a2b3c4d5e6f
docker start <container_id>	Start a stopped container	docker start 1a2b3c4d5e6f
docker rm <container_id>	Remove a stopped container	docker rm 1a2b3c4d5e6f
docker rmi <image_name>	Remove an image	docker rmi python:3.8
docker logs <container_id>	View logs of a container	docker logs 1a2b3c4d5e6f
docker exec -it <container_id> <command>	Execute a command inside a running container	docker exec -it 1a2b3c4d5e6f bash
docker build -t <image_name> <path>	Build an image from a Dockerfile	docker build -t myapp:latest .
docker inspect <container_id>	Get detailed information about a container	docker inspect 1a2b3c4d5e6f

What is a Dockerfile

A Dockerfile is a plain text file without an extension that contains a list of step-by-step instructions for automatically building a Docker image.

Dockerfile Instructions

• FROM: Uses an existing image

• WORKDIR: Defines the working directory inside the container

• COPY: Copies selected files from the host system into the container

• RUN: Executes a command

• EXPOSE: Exposes a port to the outside world

• CMD: The command that runs when the container starts

Docker Volumes

What is a volume in Docker?

In Docker, a volume is a persistent storage mechanism that allows you to store data outside of the container's filesystem. Volumes are used to persist data generated by and used by Docker containers. They are managed by Docker and can be shared between multiple containers, making them ideal for scenarios where you need to maintain state or share data.

---

Summary of Docker Volumes:

Volumes persist data generated by containers and can be shared between multiple containers. They are managed by Docker and can be used to persist data even after the container is stopped or removed. Volumes are stored in a part of the host filesystem managed by Docker (/var/lib/docker/volumes/ on Linux).

---

Table of Docker Volume Commands:

Command	Description	Example
docker volume create <volume_name>	Create a new volume	docker volume create myvolume
docker run -d -v <volume_name>:/path/in/container <image_name>	Run a container with a volume attached	docker run -d -v myvolume:/data nginx
docker volume ls	List all volumes	docker volume ls
docker volume inspect <volume_name>	Get detailed information about a volume	docker volume inspect myvolume
docker volume rm <volume_name>	Remove a volume	docker volume rm myvolume

Docker Networks

What is a Docker network?

In Docker, a network is a virtual layer that allows containers to communicate with each other and with the outside world. Docker provides several built-in network drivers, such as bridge, host, overlay, and macvlan, each serving different use cases. Networks enable containers to discover and interact with each other using container names or IP addresses.

Summary of Docker Networks:

Networks allow containers to communicate with each other securely. By default, containers on the same network can communicate with each other using container names.

Types of Docker Networks:

Network Type	Description	Use Case
bridge	Default network driver for standalone containers. It creates a private internal network on the host	Suitable for single-host container communication
host	Removes network isolation between the container and the Docker host, allowing the container to use the host's network directly	Useful for performance-sensitive applications that require direct access to the host network
overlay	Enables communication between containers across multiple Docker hosts, typically used in Docker Swarm or Kubernetes	Ideal for multi-host container communication in a cluster environment
macvlan	Assigns a MAC address to a container, allowing it to appear as a physical device on the network	Useful for scenarios where containers need to be treated as physical devices on the network

Table of Docker Network Commands:

Command	Description	Example
docker network create <network_name>	Create a new network	docker network create mynetwork
docker run --network <network_name> <image_name>	Run a container attached to a specific network	docker run --network mynetwork nginx
docker network ls	List all networks	docker network ls
docker network inspect <network_name>	Get detailed information about a network	docker network inspect mynetwork
docker network connect <network_name> <container_name>	Connect a container to a network	docker network connect mynetwork mycontainer
docker network disconnect <network_name> <container_name>	Disconnect a container from a network	docker network disconnect mynetwork mycontainer

Port Mapping in Docker Networks:

Port mapping allows you to expose container ports to the host machine, enabling external access to services running inside containers. This is typically done using the -p or --publish flag when running a container.

docker run -d -p <host_port>:<container_port> <image_name>

Docker Compose

What is Docker Compose?

Docker Compose is a tool that allows you to define and manage multi-container Docker applications. It uses a YAML file to configure the application's services, networks, and volumes, making it easier to set up and run complex applications with multiple interconnected containers. With Docker Compose, you can start all the services defined in the configuration file with a single command, simplifying the development and deployment process.

Summary

Docker Compose allows you to define multi-container applications in a single file, making it easier to manage and deploy complex applications. It provides a simple way to start, stop, and scale services, as well as manage networks and volumes.

Docker Compose Example

services:
  web:
    image: nginx:latest
	ports:
	  - "80:80"
	volumes:
	  - ./html:/usr/share/nginx/html
  db:
	image: mysql:5.7
	environment:
	  MYSQL_ROOT_PASSWORD: example
	  MYSQL_DATABASE: mydb
	  MYSQL_USER: user
	  MYSQL_PASSWORD: password

---

Basic Commands

Command	Description
docker compose up	Starts the services defined in the docker-compose.yml file.
docker compose down	Stops and removes the containers, networks, and volumes created by up.
docker compose up -d	Starts the services in detached mode, running them in the background.
docker compose ps	Displays the status of the services defined in the docker-compose.yml file.
docker compose logs	View logs of services
docker compose build	Builds or rebuilds the services defined in the docker-compose.yml file.
docker compose restart	Restarts the services defined in the docker-compose.yml file.