Docker Tutorial: A Comprehensive Guide to Getting Started¶

What is Docker?¶

Docker is a containerization platform that allows developers to package, ship, and run applications in containers. Containers are lightweight and portable, providing a consistent and reliable way to deploy applications. Docker enables developers to create, deploy, and manage applications more efficiently, making it a popular choice among developers and organizations.

Docker Basics¶

Images¶

Docker images are templates that define the environment and dependencies required to run an application. Images are used to create containers. An image typically includes the following components:

Base image: A minimal Linux distribution, such as Ubuntu or Alpine Linux.
Application code: The code for the application, including dependencies and libraries.
Configuration files: Configuration files for the application, such as environment variables or settings files.
Metadata: Metadata about the image, such as its name, version, and author.

Containers¶

Docker containers are instances of images. Containers run the application and its dependencies, isolated from the host system. Containers provide a consistent and reliable way to deploy applications, with the following benefits:

Lightweight: Containers are lightweight, with a small footprint compared to virtual machines.
Portable: Containers are portable, allowing developers to deploy applications across different environments and platforms.
Isolated: Containers are isolated, providing a secure and reliable way to deploy applications.

Volumes¶

Docker volumes provide persistent storage for containers. Volumes allow data to be shared between containers and the host system. Volumes are useful for storing data that needs to be persisted across container restarts, such as database files or user data.

Docker Concepts¶

Containerization¶

Containerization is the process of packaging an application and its dependencies into a container. Containerization provides a consistent and reliable way to deploy applications, with the benefits of isolation, portability, and efficiency.

Layering¶

Docker images are composed of layers, which are stacked on top of each other to form the final image. Each layer represents a change to the image, such as adding a new file or updating a dependency. Layering provides an efficient way to build and deploy images, with the benefits of reduced storage usage and faster deployment times.

Networking¶

Docker provides a built-in networking system that allows containers to communicate with each other. Containers can be connected to a network, allowing them to communicate with other containers and the host system. Docker networking provides a flexible and scalable way to deploy applications, with the benefits of isolation and security.

Docker Components¶

Docker Engine¶

The Docker Engine is the core component of Docker, responsible for managing containers and images. The Docker Engine provides a RESTful API for interacting with containers and images, allowing developers to automate and script Docker workflows.

Docker Hub¶

Docker Hub is a public registry of Docker images, providing a centralized location for sharing and discovering images. Docker Hub allows developers to push and pull images, making it easy to share and deploy applications.

Docker Compose¶

Docker Compose is a tool for defining and running multi-container applications. Docker Compose allows developers to define a YAML file that describes the services and dependencies for an application, making it easy to deploy and manage complex applications.

General tips¶

By default, docker data is not persistent. You need to create a separate volume and use it in the container for persistence. The other way to do this is bind mount where you specify host folder as a folder available in container.
Docker containers are ephemeral. If you stop a container, all the data inside it is lost. You can use volumes to persist data.
Docker containers are isolated from the host system. They have their own filesystem and network stack.
Bind mounts can be used for persisting data between the host and the container.

Installing Docker on Debian¶

Install Docker with this one command

curl -fsSL https://get.docker.com | sudo sh
#This can be unsafe is url is incorrect or pointing to some rouge script.
# you are giving root access to a script at this location. :)
# Follow below steps, if you want to install manually.

#Give the current user docker group permissions
sudo usermod -aG docker $USER

#The docker service starts automatically on Debian based distributions after this method of installation.

To install Docker manually on Debian, follow these steps:

# Add Docker's official GPG key:
sudo apt-get update
sudo apt-get install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/debian/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

# Add the repository to Apt sources:
#Replace this part with the codename of the corresponding Debian release, such as bookworm.
echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/debian \
  $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update


# Install latest version
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Verifying Docker Installation¶

To verify that Docker is installed correctly, run the following command:

bash
docker --version

sudo docker run hello-world

This should display the version of Docker that is installed.

Creating a Docker Container

To create a Docker container, follow these steps:

Pull the official Ubuntu image:

bash docker pull ubuntu

2.  Run a new container from the Ubuntu image:
    ```
bash
docker run -it ubuntu /bin/bash

This will start a new container from the Ubuntu image and open a bash
1
2
3 shell inside the container.

1. Inside the container, you can run commands and install packages just like you would on a regular Ubuntu system. For example, you can install the `nginx` web server:

bash
apt update
apt install nginx
1
2
3 1. Once you've installed and configured the software you need, you can exit the container by typing `exit`.

2. To verify that the container is still running, you can use the `docker ps` command:

bash
docker ps
1
2
3 This will display a list of running containers, including the one you just created.

1. To stop the container, you can use the `docker stop` command:

bash
docker stop <container_id>
1
2
3 Replace `<container_id>` with the ID of the container you want to stop.

1. To restart the container, you can use the `docker start` command:

bash
docker start <container_id>

Replace <container_id> with the ID of the container you want to restart.

Managing Containers¶

Docker provides several commands for managing containers. Here are a few examples:

docker ps: Displays a list of running containers.
docker stop: Stops a running container.
docker start: Starts a stopped container.
docker restart: Restarts a running container.
docker rm: Deletes a stopped container.
docker logs: Displays the logs for a container.
docker exec: Runs a command inside a running container.

Docker image¶

Docker images are templates that define the environment and dependencies required to run an application. Images are used to create containers.

docker pull: Pulls an image from a registry.
docker build: Builds an image from a Dockerfile.
docker push: Pushes an image to a registry.
docker tag: Tags an image with a name and version.
docker image ls: Displays a list of images.
docker image rm: remove images.
docker image prune: Remove unused images.

Docker Volumes¶

Docker volumes provide persistent storage for containers. Volumes allow data to be shared between containers and the host system.

docker volume create: Creates a new volume. Default linux location: /var/lib/docker/volumes/
docker volume ls: Displays a list of volumes.
docker volume rm: Deletes a volume.
docker volume inspect: Displays detailed information about a volume.

Docker Networking¶

Docker provides a built-in networking system that allows containers to communicate with each other and the host system. Here are some key concepts and commands related to Docker networking:

Docker Network Types¶

Docker provides several types of networks:

Bridge Network: The default network type, which allows containers to communicate with each other on the same host.
Host Network: Allows containers to use the host's network stack, providing direct access to the host's network interfaces.
None Network: Disables networking for a container.
Overlay Network: Allows containers to communicate with each other across multiple hosts.
Macvlan Network: Allows containers to use a MAC address and communicate directly with the host's network interfaces.

Docker Network Commands¶

Here are some key Docker network commands:

docker network create: Creates a new network.
docker network ls: Displays a list of networks.
docker network rm: Deletes a network.
docker network inspect: Displays detailed information about a network.
docker network connect: Connects a container to a network.
docker network disconnect: Disconnects a container from a network.

Docker Compose¶

Docker Compose is a tool for defining and running multi-container applications. Here are some key concepts and commands related to Docker Compose:

Docker Compose Files¶

Docker Compose uses YAML files to define the services and dependencies for an application.

version: Specifies the version of the Compose file format.
services: Defines the services that make up the application.
volumes: Defines the volumes that are shared between services.
networks: Defines the networks that are used by the services.

Docker Compose Commands¶

Here are some key Docker Compose commands:

docker-compose up: Starts the services defined in the Compose file.
docker-compose down: Stops the services defined in the Compose file.
docker-compose ps: Displays a list of running services.
docker-compose logs: Displays the logs for a service.
docker-compose exec: Runs a command inside a running service.

Best Practices for Docker¶

Here are some best practices to keep in mind when working with Docker:

Security¶

Use official images: Whenever possible, use official images from Docker Hub to minimize the risk of vulnerabilities.
Keep images up-to-date: Regularly update your images to ensure you have the latest security patches.
Use non-root users: Run containers as non-root users to reduce the risk of privilege escalation.
Limit capabilities: Limit the capabilities of containers to prevent them from accessing sensitive resources.

Networking¶

Use Docker networks: Use Docker networks to manage container communication and reduce the risk of exposure.
Limit exposure: Limit the exposure of containers to the host network and other containers.
Use DNS: Use DNS to manage container naming and discovery.

Storage¶

Use Docker volumes: Use Docker volumes to manage persistent storage and reduce the risk of data loss.
Limit storage access: Limit the access of containers to sensitive storage resources.
Use storage drivers: Use storage drivers to manage storage resources and improve performance.

Monitoring and Logging¶

Monitor container performance: Monitor container performance to identify issues and optimize resource utilization.
Collect logs: Collect logs from containers to troubleshoot issues and improve security.
Use monitoring tools: Use monitoring tools to manage container performance and logs.

Backup and Recovery¶

Backup containers: Backup containers regularly to prevent data loss.
Use backup tools: Use backup tools to manage container backups and improve recovery times.
Test backups: Test backups regularly to ensure they are valid and recoverable.

Troubleshooting Docker¶

Here are some common issues and solutions for troubleshooting Docker:

Container Issues¶

Container not starting: Check the container logs for errors and ensure the container has sufficient resources.
Container crashing: Check the container logs for errors and ensure the container has sufficient resources.
Container not responding: Check the container logs for errors and ensure the container has sufficient resources.

Networking Issues¶

Container not accessible: Check the container's network configuration and ensure it is exposed to the host network.
Container not communicating with other containers: Check the container's network configuration and ensure it is connected to the correct network.
Container not resolving DNS: Check the container's DNS configuration and ensure it is resolving correctly.

Storage Issues¶

Container not accessing storage: Check the container's storage configuration and ensure it has access to the correct storage resources.
Container not persisting data: Check the container's storage configuration and ensure it is using persistent storage.
Container running out of storage space: Check the container's storage configuration and ensure it has sufficient storage resources.