Docker Explained – An Introductory Guide To Docker

Docker Explained

Docker is an open-source platform for developing, deploying, and running applications in containers. Containers are lightweight, portable, and self-contained environments that can run on any machine, regardless of its operating system or hardware. Docker has become increasingly popular in recent years because it simplifies the deployment and scaling of applications.

Docker containers are built from images, which are essentially snapshots of a Docker container’s file system and its configuration. Docker images can be built from scratch or based on existing images, which can be customized to fit specific needs. Images can be easily shared and distributed via Docker registries, such as Docker Hub.

Docker containers offer several advantages over traditional virtual machines. They are much more lightweight, as they share the host machine’s kernel and only include the application and its dependencies. They also offer greater flexibility and scalability, as containers can be quickly and easily deployed and replicated.

In this blog, the following Docker concepts will be covered:

• History Before Containerization
• Reasons to use containers
• What is Docker?
• Dockerfile, Images, and Containers
• Docker Compose and Docker Swarm

Docker Explained: What is Docker?

Docker is a platform that enables developers to create, deploy, and run applications in containers. It provides a command-line interface (CLI) and API for interacting with containers, as well as a number of tools for managing and deploying containerized applications.

As you can see in the diagram, each and every application runs on separate containers and has its own set of dependencies and libraries. This makes sure that each application is independent of other applications, giving developers reassurance that they can build applications that will not interfere with one another.

So a developer can build a container having different applications installed on it and give it to the QA team. Then the QA team would only need to run the container to replicate the developer’s environment.

Docker has gained immense popularity in this fast-growing IT world. Organizations are continuously adopting Docker in their production environment. I take this opportunity to explain Docker in the most simple way.

Since Docker is a containerization platform, understand the history behind containerization.

Docker Explained: History Before Containerization 

Before the advent of containerization, applications were typically run on physical servers or virtual machines, which could be time-consuming to provision and manage. Virtual machines provided some advantages over physical servers, such as the ability to easily create and manage multiple instances of an application, but they were still relatively heavyweight and resource-intensive.

Containerization, on the other hand, is a lightweight alternative to virtual machines that isolates applications and their dependencies at the operating system level. This approach offers several advantages over traditional virtual machines, including improved portability, efficiency, and scalability.

The history of Docker can be traced back to the early days of containerization, when technologies such as FreeBSD jails and Solaris Zones were used to provide lightweight, isolated environments on UNIX-based systems. These technologies were limited to specific operating systems and lacked the flexibility and portability of modern containerization solutions.

In 2008, Google introduced the concept of Linux containers, which allowed multiple isolated user-space instances to run on a single kernel. This technology formed the basis for several early containerization solutions, including LXC and OpenVZ.

In 2013, Docker was launched as an open-source project based on the Linux container technology. Docker quickly gained popularity among developers and DevOps teams due to its ease of use, portability, and compatibility with a wide range of programming languages and platforms.

Since then, Docker has continued to evolve and expand, adding features such as Docker Compose, Docker Swarm, and Docker Kubernetes to support container orchestration and management at scale. The company behind Docker, Docker Inc., was founded in 2013 and has since become a major player in the containerization market.

These drawbacks led to the emergence of a new technique called containerization.

Containerization

Containerization is a method of deploying and running applications in a lightweight, portable, and isolated environment called a container. Containers provide a standardized way of packaging an application and its dependencies, enabling it to run consistently across different environments and infrastructures.

Containers are created from images, which are essentially pre-configured templates that contain all the necessary files, libraries, and dependencies required to run an application. Images can be customized and versioned, and can be easily shared and distributed via container registries such as Docker Hub.

Containers are isolated from each other and from the host system, providing a high degree of security and stability. They share the host system’s kernel and other resources, which allows them to be much more lightweight and efficient than traditional virtual machines.

Containerization offers several advantages over other deployment methods, including:

1. Portability: Containers can be run on any host system that supports the container runtime, regardless of the underlying operating system or infrastructure.
2. Consistency: Containers ensure that the application and its dependencies are packaged and run consistently, regardless of the host system or environment.
3. Efficiency: Containers are lightweight and efficient, as they share the host system’s resources and only include the application and its dependencies.
4. Scalability: Containers can be quickly and easily replicated and scaled horizontally to meet changing demand.

Containerization has become increasingly popular in recent years, with Docker being the most widely used containerization platform. Other containerization platforms include Kubernetes, Mesos, and Docker Swarm.

Moving ahead, it’s time that you understand the reasons to use containers.

Reasons to Use Containers

There are several reasons to use containers for deploying and running applications:

1. Portability: Containers are highly portable, making it easy to move applications between different environments, such as development, testing, and production, without having to worry about compatibility issues or dependencies.
2. Consistency: Containers provide a consistent runtime environment for applications, regardless of the underlying infrastructure or operating system. This ensures that the application will behave the same way regardless of where it is deployed.
3. Resource efficiency: Containers are lightweight and do not require a full operating system to be installed on each instance, which reduces the overall resource requirements and improves the efficiency of the infrastructure.
4. Scalability: Containers can be quickly and easily replicated and scaled horizontally to meet changing demand. This enables applications to handle increased traffic or workload without requiring significant changes to the underlying infrastructure.
5. Security: Containers provide a high degree of isolation between applications, reducing the risk of security breaches or conflicts with other applications running on the same infrastructure.
6. Speed: Containers can be started and stopped quickly, reducing the time required for deployment and updates.

Now, that you have understood what containerization is and the reasons to use containers, it’s the time you understand What is Docker?

Dockerfile, Images, and Containers

Dockerfile, Docker images, and Docker containers are three important terms that you need to understand while using Docker.

Dockerfile, Images, and Containers

As you can see in the above diagram when the Dockerfile is built, it becomes a Docker image, and when we run the Docker image then it finally becomes a Docker container.

• Dockerfile: A Dockerfile is a text document that contains all the commands that a user can call on the command line to assemble an image. So, Docker can build images automatically by reading the instructions from a Docker file. You can use docker build to create an automated build to execute several command-line instructions in succession.
• Docker Image: In layman’s terms, a Docker image can be compared to a template that is used to create Docker containers. So, these read-only templates are the building blocks of a Docker container. You can use docker run it to run the image and create a container. Docker images are stored in the Docker Registry. It can be either a user’s local repository or a public repository like a Dockerhub which allows multiple users to collaborate in building an application.
• Docker Container: Docker container is a running instance of a Docker image as they hold the entire package needed to run the application. So, these are basically the ready applications created from Docker images, which is the ultimate utility of Docker.

1. Creating a Container: You can create a container by using the docker run command. The run the command takes the image name as its first argument, and any additional arguments are passed as commands to the container when it starts.

docker run -it --name my-container ubuntu:20.04

2. Running a Container: You can start, stop, and restart a container using the docker start, docker stop, and docker restart commands, respectively. You can also use the docker run command to start a container in the background, by adding the -d option.

docker start my-container

3. Managing Containers: You can list all running containers using docker ps command and all containers using docker ps -a. Also, you can remove the container by docker rm container_name.

docker ps

This is a high-level introduction to Docker, there is a lot more to explore in detail such as Dockerfile, Networking, and Volumes. Additionally, you can look into sample projects that demonstrate how to use Docker in real-world scenarios.

What are Containers?

Containers are a form of virtualization at the operating system level. They allow you to package an application and its dependencies into a single container image, which can then be run consistently across different environments.

How Does Docker Work?

Docker works by creating and managing containers, which are isolated environments for running applications. Docker achieves this by using several key components:

1. Docker Engine: The core component of Docker is the Docker Engine, which is responsible for building, running, and managing containers. The Docker Engine consists of a daemon process that runs in the background and a command-line interface (CLI) that allows users to interact with the Docker Engine.
2. Docker Images: Docker uses images as the building blocks for containers. An image is a read-only template that contains all the necessary files, libraries, and dependencies required to run an application. Images can be built from scratch or based on existing images, and can be versioned and shared with other users via container registries.
3. Docker Containers: Containers are isolated environments that run on top of the Docker Engine. Each container is created from an image and contains a complete runtime environment for the application, including the application code, dependencies, and configuration. Containers can be easily started, stopped, and deleted, and can communicate with each other via network connections.
4. Docker Registries: Docker Registries are repositories for storing and sharing Docker images. The most commonly used registry is Docker Hub, which is a public registry that allows users to store and share images with other users. Docker Hub also provides a platform for discovering and downloading images created by other users.

To use Docker, you first need to install the Docker Engine on your system. Once installed, you can use the Docker CLI to interact with the Docker Engine and perform tasks such as building images, running containers, and managing container networks and volumes.

To run an application in a Docker container, you first need to create an image that contains the application code and its dependencies. You can do this by writing a Dockerfile, which is a script that defines the steps required to build an image. Once the image is built, you can use the Docker CLI to start a container from the image, which will run the application in an isolated environment.

Docker Explained: Docker Compose and Docker Swarm

Docker Compose and Docker Swarm are two tools that are commonly used with Docker to manage containerized applications and orchestrate container deployments.

Docker Compose is a tool that allows developers to define and run multi-container applications with Docker. It uses a YAML file to define the services, networks, and volumes required for the application, and can start and stop containers as a single unit. Docker Compose simplifies the process of managing complex, multi-container applications by providing a simple and standardized way to define and manage them.

Docker Swarm, on the other hand, is a container orchestration tool that allows users to manage large-scale container deployments across multiple hosts. It provides a way to scale and manage containerized applications across a cluster of Docker hosts, and includes features such as service discovery, load balancing, and rolling updates. Docker Swarm simplifies the process of managing and scaling container deployments by providing a unified interface for managing containers across multiple hosts.

While both Docker Compose and Docker Swarm provide similar functionality for managing containerized applications, they are designed for different use cases. Docker Compose is designed for local development and testing, where developers need to spin up multiple containers to test their applications. Docker Swarm is designed for large-scale production deployments, where applications need to be managed across multiple hosts.

Conclusion:

Docker has revolutionized the way that applications are developed, deployed, and managed. By using containers to isolate applications from the underlying infrastructure, Docker provides a consistent and portable runtime environment that can be easily moved between different environments.

The key benefits of using Docker include portability, consistency, resource efficiency, scalability, security, and speed. Docker enables developers and DevOps teams to build and deploy applications quickly and reliably, while also reducing the risk of conflicts and security breaches.

In addition to the core Docker Engine, Docker Compose and Docker Swarm provide powerful tools for managing containerized applications and orchestration container deployments at scale. By using these tools, developers and DevOps teams can simplify the process of managing complex, multi-container applications and enable large-scale container deployments across multiple hosts.

Overall, Docker has become an essential tool for modern software development and DevOps practices, enabling teams to build and deploy applications more efficiently, reliably, and securely.