What is Docker ?
In this article we are going to discuss Docker, what it is, what it is used for? Let's start
To understand docker first and foremost we need to understand what is the problem statement that docker is trying to resolve.
For example whenever you develop any website using PHP or may be asp.net or any other project and move that project onto the server there are definitely some uncertainties that occurs may be your images are not being loaded properly may be the path little bit different or glitchy in some of these cases that is a classic example when everything works on the developer machine but as soon as it moves to another place it doesn't work like that.
While running on the projects on other machines, There are some reasons to fail to project work on that machine such as, while running the project on another machine it might have some dependencies not installed on those machines or may be the path little bit different etc.
Docker is designed to specifically address this problem. Docker is compatible with any programming language or any project. Docker allows you to create absolutely sealed tight containers and these containers are very powerful and consist of a lot of things. These containers are a very important part of docker. These containers wrap up your entire code, dependencies, configuration, some of the processes running in the system, networking information and some of the special cases consist of the chunk of the operating system that is responsible for tweaking out something in your code. These containers are absolutely portable. When you put this container on other machines, this container works absolutely and exactly like how it worked on the developer machine.
“Docker is an open platform for developing, shipping, and running applications. Docker enables you to separate your applications from your infrastructure so you can deliver software quickly. With Docker, you can manage your infrastructure in the same ways you manage your applications. By taking advantage of Docker’s methodologies for shipping, testing, and deploying code quickly, you can significantly reduce the delay between writing code and running it in production.”
Docker contains three main essential things: first client side application - you can just install the docker. Second - it acts as a service that can be deployed on to any server. Third - you can share your docker image hence someone wants to start with a specific checkpoint, it can be started.
Docker provides the capability to package and run the project in an isolated environment known as the container. Security and isolation allow you to run multiple containers simultaneously on the host operating system. These containers are lightweight and contain all necessary things needed to run the application. You can share the container while you are working.
Docker uses a client-server architecture. The Docker client talks to the Docker daemon, which does the work of building, running, and distributing your Docker containers. The Docker client and the daemon can run on an equivalent system, or you can connect the Docker client to a remote Docker daemon. Docker clients and daemons communicate using REST APIs over UNIX sockets or network interfaces. Another Docker client is Docker Compose, which allows you to work with applications consisting of a group of containers.
Docker contains the following these things :
Docker engines : Docker engines containerization technology for building and containerizing your application. It contains three major parts: 1. Docker CLI 2. Docker API 3. Docker Daemon
Docker CLI uses Docker API to control or communicate with docker daemon through CLI commands. Docker daemon responsible for creating and managing docker objects like docker image, container, volumes and networks etc.
Docker objects : You use images, containers, networks, volumes, while you are working with Docker. These are the Docker objects.
Docker Images : Docker image is a read only template that contains the instructions to create containers that can run docker platforms. It provides a way to package up apps and a preconfigured server environment. Docker Image consists of files or layers that pack up together all the necessary things such as dependencies, source code, libraries. Docker image is made up of multiple layers and it is stored on docker registry such as docker hub or local registry.
Containers : When you run the docker image, it creates the docker container that contains all the applications and their environment run inside the container.
Volume : Volume is the perfect mechanism for continuous data generated by and used by docker containers. It is managed by the docker CLI and docker API.
Networks : Docker networking is a medium through which all the isolated containers communicate.
Docker registry : A registry is a storage and content delivery system, holding named Docker images, available in different tagged versions. Users can interact with a registry using docker push and pull command.
Docker compose : It is a tool that helps define and share multi-container applications. With compose, we can create a YAML file to define the services and with a single command, can spin everything up or tear it all down.
Docker swarm: It is a set of physical and virtual machines that run on the docker application. You can still run the docker command that you are used to even if a set of machines have been clustered together, but they will now be carried out by the machines in your cluster. Activities of the cluster are managed by the swarm manager and machines that have joined the cluster are known as nodes. It is a container orchestration tool, it allows the user to manage the multiple containers deployed across the multiple host machines.
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