Docker : Unlocking the Power of Containerization

Introduction to Docker

Docker is a set of platform as a service products that use OS-level virtualisation to deliver software in packages called containers. Containers are isolated from one another and bundle their own software, libraries and configuration files; they can communicate with each other through well-defined channels. All containers are run by a single operating-system kernel and are thus more lightweight than virtual machines.

Containers

Docker Container is a standardised unit which can be created on the fly to deploy a particular application or environment. It could be an Ubuntu container, CentOs container, etc. to full-fill the requirement from an operating system point of view. Also, it could be an application oriented container like CakePHP container or a Tomcat-Ubuntu container etc.

Virtual Machines

A Virtual Machine (VM) is created to perform tasks that if otherwise performed directly on the host environment, may prove to be risky. VMs are isolated from the rest of the system; the software inside the virtual machine cannot tamper with the host computer. Therefore, implementing tasks such as accessing virus-infected data and testing of operating systems are done using virtual machines. We can define a virtual machine as:

A virtual machine is a computer file or software usually termed as a guest, or an image that is created within a computing environment called the host.

Containers v/s Virtual Machines

lets discuss the key differences:

• Virtual Machines are slow and take a lot of time to boot.

• Containers are fast and boots quickly as it uses host operating system and shares the relevant libraries.

• Containers do not waste or block host resources unlike virtual machines.

• Containers have isolated libraries and binaries specific to the application they are running.

• Containers are handled by Containerisation engine.

• Docker is one of the containerisation platforms which can be used to create and run containers.

Knowledge Check - 1

Docker Architecture

Docker uses a client-server architecture. The Docker client talks to the Docker daemon, which does the heavy lifting of building, running, and distributing your Docker containers. The Docker client and daemon can run on the same system, or you can connect a Docker client to a remote Docker daemon. The Docker client and daemon communicate using a REST API, over UNIX sockets or a network interface. Another Docker client is Docker Compose, that lets you work with applications consisting of a set of containers.

Docker daemon

The Docker daemon (dockerd) listens for Docker API requests and manages Docker objects such as images, containers, networks, and volumes. A daemon can also communicate with other daemons to manage Docker services.

Docker client

The Docker client (docker) is the primary way that many Docker users interact with Docker. When you use commands such as docker run, the client sends these commands to dockerd, which carries them out. The docker command uses the Docker API. The Docker client can communicate with more than one daemon.

Docker registries

A Docker registry stores Docker images. Docker Hub is a public registry that anyone can use, and Docker looks for images on Docker Hub by default. You can even run your own private registry.

When you use the docker pull or docker run commands, Docker pulls the required images from your configured registry. When you use the docker push command, Docker pushes your image to your configured registry.

Docker objects

When you use Docker, you are creating and using images, containers, networks, volumes, plugins, and other objects. This section is a brief overview of some of those objects.

Images

An image is a read-only template with instructions for creating a Docker container. Often, an image is based on another image, with some additional customization. For example, you may build an image which is based on the ubuntu image, but installs the Apache web server and your application, as well as the configuration details needed to make your application run.

Containers

A container is a runnable instance of an image. You can create, start, stop, move, or delete a container using the Docker API or CLI. You can connect a container to one or more networks, attach storage to it, or even create a new image based on its current state. By default, a container is relatively well isolated from other containers and its host machine. You can control how isolated a container's network, storage, or other underlying subsystems are from other containers or from the host machine.

A container is defined by its image as well as any configuration options you provide to it when you create or start it. When a container is removed, any changes to its state that aren't stored in persistent storage disappear.

Install Docker Engine

The best way to get started developing containerized applications is with Docker Desktop, for OSX or Windows. Docker Desktop will allow you to easily set up Kubernetes or Swarm on your local development machine, so you can use all the features of the orchestrator you’re developing applications for right away, no cluster required.

1. Download the installer using the download button at the top of the page, or from the release notes.

2. Double-click Docker Desktop Installer.exe to run the installer. By default, Docker Desktop is installed at C:\Program Files\Docker\Docker.

3. When prompted, ensure the Use WSL 2 instead of Hyper-V option on the Configuration page is selected or not depending on your choice of backend.

   If your system only supports one of the two options, you will not be able to select which backend to use.

4. Follow the instructions on the installation wizard to authorize the installer and proceed with the install.

5. When the installation is successful, select Close to complete the installation process.

Happy Dockerizing!

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