Docker fundamentals

Containerize using Docker

Docker is an open-source platform that enables developers to automate the deployment and packaging of applications into containers. Containers are lightweight, standalone, and executable software packages that contain all the necessary dependencies and configuration to run an application.

Here's how Docker and containers work:

Containerization: Docker uses containerization technology to create isolated environments called containers. Each container includes the application code, runtime, system tools, libraries, and dependencies. Containers are built from images, which are read-only templates that define the initial state of a container.
Docker Image: A Docker image is a lightweight, portable, and self-sufficient package that contains everything needed to run an application. It includes the application code, runtime environment, system libraries, and dependencies. Images are created from a set of instructions called a Dockerfile, which specifies how to build the image.
Docker Engine: The Docker Engine is the runtime that runs and manages containers. It provides an interface to build, run, and manage containers on a host machine. Docker Engine includes a client-server architecture, where the Docker client communicates with the Docker daemon, which handles container operations.
Portability: Containers created with Docker are highly portable. They can run on any machine that has Docker installed, regardless of the underlying operating system or infrastructure. This portability makes it easier to develop, test, and deploy applications across different environments.
Isolation: Containers offer a level of isolation between applications and the underlying host system. Each container runs in its own isolated environment, ensuring that applications and their dependencies do not interfere with each other. This isolation improves security and allows multiple containers to run on the same host without conflicts.
Resource Efficiency: Containers are lightweight and share the host machine's operating system kernel. They consume fewer resources compared to traditional virtual machines (VMs) since they do not require a separate operating system for each container. This efficiency allows for higher density and better utilization of system resources.
Rapid Deployment: Docker simplifies the deployment process by packaging applications into containers. Containers can be easily created, deployed, and scaled up or down as needed. This speed and agility in deploying applications make it ideal for modern application architectures and continuous integration/continuous deployment (CI/CD) pipelines.

Docker is an open-source platform that automates the deployment, scaling, and management of applications using containerization. It provides a lightweight and portable environment for running applications in containers. Docker's architecture consists of several components working together to enable efficient containerization. Here's a detailed explanation of Docker and its architecture:

Docker Architecture Components:

Docker Engine:
Docker Daemon: It runs as a background process on the host system and is responsible for managing Docker objects, such as containers, images, networks, and storage volumes.
Docker Client: It is a command-line interface (CLI) tool that allows users to interact with the Docker Daemon. Users issue commands to the Docker Client, which communicates with the Docker Daemon to execute those commands.
REST API: Docker provides a RESTful API that enables programmatic control and management of Docker resources. The API allows developers to interact with Docker programmatically.
Docker Images:
Docker Images are the building blocks of containers. An image is a lightweight, standalone, and executable software package that includes everything needed to run an application, such as code, runtime environment, libraries, and dependencies.
Images are created from Dockerfiles, which are text files containing instructions for building the image. Dockerfiles define the base image, add dependencies, copy files, set environment variables, and specify commands to run when a container is started.
Docker Containers:
Docker Containers are instances of Docker Images that are running and isolated from each other. Each container runs as a separate process and has its own file system, networking, and resources.
Containers can be started, stopped, paused, and restarted using Docker commands. They encapsulate the application and its dependencies, providing an isolated and consistent runtime environment.
Docker Registry:
Docker Registry is a central repository that stores Docker Images. It allows users to share and distribute images across different environments and users.
The default public Docker Registry is Docker Hub, which hosts a vast collection of public images. However, you can also set up private registries to store and share images within your organization.
Docker registries use the Docker Registry API for image push, pull, and management operations.

Docker Workflow:

Writing a Dockerfile: A Dockerfile is a text file that contains instructions for building a Docker Image. It specifies the base image, adds dependencies, copies files, sets environment variables, and defines the commands to run when a container is started.
Building Images: Docker builds images based on Dockerfiles using the Docker build command. It executes the instructions in the Dockerfile and creates a layered image that represents the application and its dependencies.
Running Containers: Docker allows you to create, run, and manage containers based on the built images. Containers can be started, stopped, paused, and restarted using Docker commands. You can also configure networking, storage volumes, and resource allocation for containers.
Container Orchestration: Docker can be integrated with container orchestration platforms like Kubernetes to manage and scale containerized applications across a cluster of machines. These platforms handle container scheduling, scaling, load balancing, and fault tolerance.
Docker Registry Usage: Docker Images can be pushed to and pulled from a Docker Registry. You can use public registries like Docker Hub or set up private registries to store and share images within your organization.

Benefits of Docker:

Portability: Docker allows applications to be packaged into self-contained containers, which can be deployed on any system running Docker. This provides portability and eliminates issues related to compatibility and environment differences.
Efficiency: Docker containers are lightweight and share the host system's kernel, resulting in better resource utilization and higher application density on a single host.
Isolation: Containers provide isolation, ensuring that applications and their dependencies run in a self-contained environment without interfering with each other or the host system.
Reproducibility: Docker's image-based approach allows for easy reproducibility of application builds. The same image can be used across different environments, providing consistency and reducing deployment-related issues.
Scalability: Docker enables efficient scaling of applications by allowing multiple instances of containers to be deployed and managed easily, either manually or through container orchestration platforms like Kubernetes.
Collaboration: Docker facilitates collaboration among development teams by providing a standardized and easily shareable environment. Developers can work on the same image and share it across the development lifecycle.

Docker's architecture and features make it a popular choice for containerization, enabling developers to streamline application deployment, improve scalability, enhance collaboration, and achieve consistent and reliable application delivery.

Docker installation and configuration on Linux

Docker has become widely adopted due to its ease of use, portability, and ecosystem of tools and services. It revolutionized the software development and deployment process by providing a standardized way to package and distribute applications, making it easier to build and deploy software in a consistent and reproducible manner.

Installing and configuring Docker on Linux involves several steps to ensure a successful setup. The following is a detailed explanation of how to install and configure Docker on a Linux system:

Check System Requirements:

Ensure that your Linux system meets the requirements for Docker installation. Generally, Docker requires a 64-bit version of Linux with a kernel version of 3.10 or higher.

Uninstall Older Docker Versions (if applicable):

If you have an older version of Docker installed, it is recommended to uninstall it before proceeding. Use the package manager or appropriate commands specific to your Linux distribution to remove the older version.

Update System Packages:

Before installing Docker, update your system's package repositories and packages to ensure you have the latest versions. Use the following commands based on your Linux distribution:

Debian/Ubuntu:
```
 sudo apt update

 sudo apt upgrade
```
CentOS/RHEL:
```
 sudo yum update
```
Install Docker:

The Docker installation process varies slightly depending on the Linux distribution you are using. Here are the steps for popular Linux distributions:

Debian/Ubuntu:

Install the required packages to allow apt to use a repository over HTTPS:

sudo apt install apt-transport-https ca-certificates curl software-properties-common

Add Docker's official GPG key:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

Add the Docker repository to your system:

echo "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Update the package repository and install Docker:

 sudo apt update
 sudo apt install docker-ce docker-ce-cli containerd.io

CentOS/RHEL:

Install required packages:

sudo yum install -y yum-utils device-mapper-persistent-data lvm2

Set up Docker's repository:

 sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

Install Docker:

sudo yum install docker-ce docker-ce-cli containerd.io

Start and Enable Docker:

After installing Docker, start the Docker service and enable it to start automatically on system boot. Use the following commands:

        sudo systemctl start docker
        sudo systemctl enable docker

Verify Docker Installation:

Verify that Docker is installed correctly by running a simple Docker command:

        docker --version

This should display the Docker version installed on your system.
Configure Docker for Non-root Users (Optional):

By default, Docker requires root or sudo privileges to execute Docker commands. If you want to allow a non-root user to run Docker commands, you can add the user to the "docker" group:

        sudo usermod -aG docker your_username

After adding the user to the "docker" group, the user will need to log out and log back in for the changes to take effect.

Docker should now be successfully installed and configured on your Linux system. You can start using Docker to create, run, and manage containers. Remember to refer to Docker's documentation for more advanced configuration and usage options.