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What is Docker? Complete Guide 2023

February 15, 2024

Creating software applications often requires dealing with intricate databases, programming languages, frameworks, and dependencies, among other things. Additionally, when collaborating with various Operating Systems (OSs), you may encounter issues with compatibility.

Each of these factors has the potential to impede your progress. This is where Docker can provide a solution. It allows you to create and oversee applications within containerized environments. As a result, Docker can not only remove many complicated configuration tasks but also make development easier and more efficient.

According to the Stack Overflow Developer Survey 2022, Docker is becoming an equally essential tool as Git for professional developers, with the Docker adoption rates rising from 55% to 69% between 2021 and 2022.

In this article, we’ll share a complete guide on what Docker is, how it works, its architecture, and its pros and cons to help you start.

Let’s dive right in!

Getting familiar with Docker and containerization

Docker is an open-source platform that allows you to create, deploy, and manage applications inside containers. It scales your applications quickly and easily by deploying multiple containers that run the same application. Therefore, you can easily manage and orchestrate these containers using tools like Docker Compose or Kubernetes.

Containerization is a method of packaging and running software applications to ensure consistency and reliability across different computing environments. It allows developers to package an application and all its dependencies into a self-contained container.

Docker is a popular tool for implementing containerization. It provides a powerful solution for modern software development, simplifying the process of building and deploying applications across multiple environments while ensuring consistency and reliability.

How does Docker work?

Docker Architecture

It’s time to learn about the creation of Docker, the software that underpins containerization.

The engine, which facilitates the creation and containerization of applications in Docker, consists of three major components:

Docker Daemon: this is the core component of the Docker engine that manages and controls the Docker containers, images, networks, and volumes. It’s a process that keeps running in the background, waiting for the commands from the client.

Docker Engine REST API: allows the user to communicate with the Daemon.

Docker CLI: command-line tool that provides a user-friendly interface for interacting with the Docker engine via the REST API.

The Docker Engine allows you to run applications stored in containers on any infrastructure. This helps make Docker the best container runtime in the industry.

Docker Image

An image is a pre-packaged, standalone software package that contains all the files, dependencies, and configurations needed to run a specific application or service. Think of it as a snapshot of a particular software environment at a specific time.

Images are instructions in a Dockerfile, specifying steps to build a container.

Each modification added to the image creates a new layer in the container, forming a sequence of stacked changes that ultimately result in the final container.

Docker Container

According to the official Docker resources, a container is a software package containing an application and all its dependencies, making it easy to run the application reliably in different computing environments. The container image is a lightweight and standalone executable package that includes everything necessary to run the application, such as the code, runtime, system libraries, tools, and settings.

Containers are created from Dockerfiles to build images. When a container starts, it runs in its own isolated namespace with a separate filesystem, network interfaces, and process tree. This allows multiple containers to run on the same host without interfering with each other, providing a level of isolation and security.

Docker containers are considered to be:

  • Lightweight: Containers don’t require a separate operating system for each application, which saves money on licensing and maintenance costs.
  • Secure: With Docker’s robust default isolation capabilities, containers provide a secure environment for applications.
  • Standard: Even though containers have been in use for many years, Docker has established the industry benchmark for their utilization. Docker containers are highly portable and simple to use.
docker guide

Docker Registry

Registry is a tool that allows you to store, manage, and distribute Docker images. It’s like a central repository where you can store your images and access them from anywhere.

By default, Docker Engine interacts with Docker’s public registry called Docker Hub. It’s a central repository for images that provides an easy-to-use web interface and API for managing and sharing images.

Some of Docker Hub’s key features are:

 

FEATURE DESCRIPTION
Private Repositories Pushing and pulling container images
Official Images Pulling and using high-quality container images provided by Docker
Automated Image Builds The process of automatically constructing container images from GitHub and Bitbucket, and pushing them to Docker Hub
Teams & Organizations Access to the repository can be limited to either the creator or the members of the organization associated with it
Webhooks After a successful push to a repository, actions can be triggered to enable the integration of Docker Hub with other services

Docker Compose

Docker Compose is a tool that allows developers to define and run multi-container Docker applications. With Compose, developers can specify the different services that make up an application, such as web servers, databases, and microservices, and how they should interact with each other.

By defining an application in a single YAML file, developers can easily spin up and manage the entire application stack with a single command. This makes it easier to develop and test complex applications, as well as deploy them to production environments.

Compose is especially useful for developers who work on microservices-based architectures, where applications are composed of multiple, independent services that need to communicate with each other. By using Compose, developers can easily manage and scale these services, while keeping the infrastructure as code in a single file.

What are the use cases of Docker?

Developers and DevOps professionals mainly use Docker for their work.Its purpose is to facilitate the creation, modification, and deployment of applications as containers that are portable and lightweight. This configuration involves packaging all necessary dependencies into a single unit, which can run on almost any operating system.

As for the Docker’s use cases, here are some of its most common applications:

  • Application development and testing: with Docker, developers can create an isolated environment for developing and testing applications, without worrying about the dependencies or clashes with other applications installed on their system.
  • Continuous integration and deployment (CI/CD):Docker can automate the building, testing, and deployment of applications. Its lightweight containers can be quickly started, speeding up the testing cycle. This feature ensures that code changes are thoroughly tested and deployed promptly.
  • Microservices architecture: with the excellent community support, Docker offers uniform development and production environments. When used in microservices architectures, Docker allows independent services to be scaled and updated separately by containerizing each of them, making it easy to manage and deploy.
  • Cloud computing: Docker containers can be deployed on cloud platforms, such as Amazon Web Services (AWS) and Google Cloud Platform (GCP), making it easier to run applications in could-based, scalable environment.
  • Legacy application migration: Docker can help migrate legacy applications to modern environments by containerizing them, making it easier to maintain and update them.

How to install Docker

The steps to install Docker depend on your operating system. Here are the general steps for installing Docker on a few common platforms:

For Windows

  1. Download Docker Desktop from the Docker website.
  2. Double-click the downloaded EXE file to run the installer.
  3. Follow the prompts to install Docker Desktop.
  4. When prompted, select “Enable WSL 2 Windows Features” and “Install required Windows components for WSL 2”.
  5. Restart your computer to complete the installation.
  6. Verify that Docker is installed and running by opening a PowerShell or Command Prompt window and running the
hello-world

command.

For macOS

  1. Download Docker Desktop from the Docker website.
  2. Double-click the downloaded DMG file to open the installer.
  3. Drag the Docker.app file to the Applications folder.
  4. Open Docker from the Applications folder and follow the prompts to install command-line tools.
  5. Verify that Docker is installed and running by opening a terminal and running the
hello-world

command

For Linux

  1. Update the package index and install required packages:

sql

sudo apt-get update sudo apt-get install apt-transport-https ca-certificates curl gnupg lsb-release
  1. Add Docker’s official GPG key:

bash

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
  1. Add Docker repository to APT sources:

bash

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
  1. Update the package index and install Docker:

sql

sudo apt-get update sudo apt-get install docker-ce docker-ce-cli containerd.io
  1. Verify that Docker is installed and running:
sudo docker run hello-world

It’s important to note that these steps are specific to Ubuntu Linux. If you are using a different distribution of Linux, the steps may vary slightly. However, the general process of adding Docker’s official GPG key and repository to package sources should be the same.

Pros and cons of Docker

Docker is a popular platform for containerization, which allows developers to package their applications and dependencies into a single, portable unit that can run consistently across different environments.

Pros

Portability: Docker provides a consistent environment across different platforms, making it easy to move applications between development, testing, and production environments. This helps streamline the development process and ensures that applications behave the same way across different environments.

Resource efficiency: Docker containers contain only the necessary code for the application and its dependencies, making them smaller in size. Running them on the cloud eliminates the need for large physical servers.

Isolation: Docker containers operate independently, so if one fails, others remain unaffected. This simplifies application management and deployment at scale.

Scalability: with Docker’s lightweight containers, you can add or remove resources quickly. As a result, it allows your application to scale rapidly to meet changing demand.

Consistency: Docker ensures that the application runs consistently, regardless of the underlying host operating system or hardware configuration.

Cons

Learning curve: Docker has a steep learning curve, especially for developers who are new to the concept of containerization. It requires a good understanding of its architecture, containerization principles, and related technologies to be able to use Docker effectively.

Compatibility: with Docker, an application designed to run on a specific operating system may not be compatible with another operating system. For example, an application designed to run in a Docker container on Windows may not be able to run on Linux, and vice versa. This can be a significant issue for organizations that have heterogeneous environments with both Windows and Linux servers.

Support for graphical interfaces: Docker is primarily designed to run server-side applications, so running applications with graphical interfaces on Docker containers can be challenging as it requires some additional workarounds.

To sum it up

Now that we’ve covered the basics of Docker, its architecture, and key terminology, you’ll have a better understanding of what Docker is and how it works.

Docker is a valuable tool that can benefit developers, system administrators, and DevOps engineers. It simplifies the containerization process, making it easier to package, deploy and run applications.

Docker’s scalability, portability, and security features make it a valuable tool with a wide range of use cases, from small-scale development environments to large-scale production deployments.

Anyone looking to streamline their application deployment process and improve infrastructure management can benefit from reading this Docker guide and incorporating Docker into their workflow.

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