Why Docker?

Previously, when a developer or system administrator needed to create a logical server on a physical server, they would use virtualization software to create a logical server from the physical server.

In this approach, logical resources were often wasted. For example, if an application required 1GB of space to run and I allocated 2GB for the logical server, 1GB of space would be wasted.

To solve this issue, the IT industry introduced a new concept called containerization. With containerization, you don't need to create a logical server from your physical server. Instead, you can install Docker Engine on your physical server and run your application as a container. The container will use the necessary binaries and libraries from the hardware or kernel.

This is why we started using Docker. Docker allows applications to run in containers, which are lightweight and portable.

Virtual Machine vs Docker Containers?

Virtual Machine is logical server created on top of the physical server by using a Hypervisor software called Oracle VirtualBox, Xen etc.

Virtual Machine consume the computing resources from physical server. If you delete the virtual machine all resources are release.

Docker Container is a lightweight, standalone, executable packages that include everything needed to run a piece of software, including the code, runtime, system tools, libraries, and settings.

Docker Container vs. Virtual Machine | Download Scientific Diagram

What is Docker?

Docker is a platform that enables developers to build, ship, and run applications inside lightweight, portable containers. Containers allow developers to package an application with all its dependencies into a standardized unit for software development.

Architecture of Docker?

Docker uses a client-server architecture. The Docker client communicates with the Docker daemon, which builds, manages, and distributes your Docker containers.

A Docker client can also be connected to a remote Docker daemon, or the daemon and client can operate on the same machine. They communicate over a REST API, over UNIX sockets, or a network interface.

A Docker registry has Docker images stored in it. The most popular public Docker registry is the Docker Hub which anyone can use.

Docker Architecture

Download & Install Docker on Ubuntu?

Update the software repositories
```
 sudo apt update
```
Install Docker
```
 sudo apt install docker.io -y
```

Enable and start the Docker service

 sudo systemctl start docker
 sudo systemctl enable docker --now

Check Docker version
```
 docker --version
```

Docker Components?

Docker Engine

Docker Engine is the core component of the Docker, It is consist of.

Docker Daemon

The Docker Daemon runs on the host machine and is responsible for building, running, and managing Docker containers. It is also known as dockerd.
Docker Client

he Docker Client is a command-line interface (CLI) tool that allows users to interact with the Docker Daemon. Users can issue commands such as docker run and docker build through the Docker Client. It is also known as docker.
REST API

Docker Engine uses a REST API to communicate between the Docker Daemon and the Docker Client, enabling programmatic control of Docker.

Docker Containers

List all running containers
```
 docker ps
```

List all running and stopped containers
```
 docker ps -a
```
Start a running container
```
 docker start container-id
```
Stop a running container
```
 docker stop container-id
```
Remove a container
```
 docker rm container-id
```
Remove all stopped containers
```
 docker container prune
```
View logs of a container
```
 docker logs container-id
```
Execute a command in running container
```
 docker exec -it container-id command
```
Attach to a running container
```
 docker attach container-id
```

Run a container

docker run -d -p 80:80 --name webserver nginx

Docker Images

Build an image from a Dockerfile
```
 docker build -t image-name
```
List all images
```
 docker images
```
Remove an image
```
 docker rmi image-id
```

Tag an image

 docker tag source-image:tag target-iamge:tag
 docker tag node-app:latest node-app:v1.0

Push an image to a registry
```
 docker push image-name
```
Pull an from a registry
```
 docker pull image-name
```

Docker Networking

List networks
```
 docker network ls
```
Create a network
```
 docker network create network-name
```
Inspect a network
```
 docker network inspect network-name
```

Connect a container to a network

 docker network connect network-name container-id

Disconnect a container from a network

 docker network disconnect network-name container-id

Docker Volumes

List volumes
```
 docker volume ls
```
Create a volume
```
 docker volume create volume-name
```
Inspect a volume
```
 docker volume inspect volume-name
```
Remove a volume
```
 docker volume rm volume-name
```
Remove all unused volumes
```
 docker volume prune
```

Mount a volume to a container

 docker run -d -v volume-name:/path/in/container image
 docker run -d -v myvolume:/app/data nginx

Docker Hub

Docker Hub is a cloud-based registry service for storing and sharing Docker images. It provides a central repository where users can find, publish, and manage Docker images. Docker Hub includes both public and private repositories.

Docker Compose

Docker Compose is a tool for defining and running multi-container Docker applications. It uses a YAML file (docker-compose.yml) to configure the application's services, networks, and volumes. With a single command (docker-compose up), users can start all the services defined in the Compose file.

Docker Swarm

Docker Swarm is Docker's native clustering and orchestration tool. It allows users to create and manage a swarm of Docker nodes (a cluster of Docker engines) and deploy services across the swarm. Swarm provides features for service discovery, load balancing, scaling, and rolling updates.

Docker Registry

A Docker Registry is a storage and distribution system for Docker images. Docker Hub is the default registry, but users can also set up their own private registries using Docker Registry, an open-source implementation of the Docker Registry API.

Dockerfile

A Dockerfile is a text file that contains a series of instructions on how to build a Docker image. It includes commands to specify the base image, copy files, install dependencies, set environment variables, and define the container's startup command.

Conclusion

Docker is a platform that simplifies application development and deployment by using containers for consistency and efficiency. Key components include Docker Engine, Docker Images, Docker Containers, Dockerfile, Docker Hub, Docker Compose, Docker Swarm, Docker Volumes, Docker Network, and Docker Registry. Docker can be installed on Ubuntu via APT, a convenience script, or Snap. A comprehensive cheat sheet provides essential commands for managing containers, images, networks, and volumes.

Understanding Docker: From Installation to Deployment

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