What is Docker?
Docker is a tool designed to make it easier to create, deploy, and run applications by using containers. Docker is based on the idea of containers, which are a way of packaging software in a format that can be easily run on any platform.

Docker provides a way to manage and deploy containerized applications, making it easier for developers to create, deploy, and run applications in a consistent and predictable way. Docker also provides tools for managing and deploying applications in a multi-container environment, allowing developers to easily scale and manage the application as it grows.

What is a container?
A container is a lightweight, stand-alone, and executable package that includes everything needed to run the software, including the application code, system tools, libraries, and runtime.

Containers allow a developer to package up an application with all of the parts it needs, such as libraries and other dependencies, and ship it all out as one package. It allows developers to package an application with all of its dependencies into a single package, making it easier to deploy and run the application on any platform. This is especially useful in cases where an application has specific requirements, such as certain system libraries or certain versions of programming languages, that might not be available on the target platform.

What is Dockerfile, Docker Image, Docker Engine, Docker Desktop, Docker Toolbox?
A Dockerfile is a text file that contains instructions for building a Docker image. It specifies the base image to use for the build, the commands to run to set up the application and its dependencies, and any other required configuration.

A Docker image is a lightweight, stand-alone, executable package that includes everything needed to run the software, including the application code, system tools, libraries, and runtime.

The Docker Engine is the runtime environment that runs the containers and provides the necessary tools and libraries for building and running Docker images. It includes the Docker daemon, which is the process that runs in the background to manage the containers, and the Docker CLI (command-line interface), which is used to interact with the Docker daemon and manage the containers.

Docker Desktop is a desktop application that provides an easy-to-use graphical interface for working with Docker. It includes the Docker Engine, the Docker CLI, and other tools and libraries for building and managing Docker containers.

Docker Toolbox is a legacy desktop application that provides an easy way to set up a Docker development environment on older versions of Windows and Mac. It includes the Docker Engine, the Docker CLI, and other tools and libraries for building and managing Docker containers. It is intended for use on older systems that do not meet the requirements for running Docker Desktop. Docker Toolbox is no longer actively maintained and is being replaced by Docker Desktop.

A Fundamental Principle of Docker:
In Docker, an image is made up of a series of layers. Each layer represents an instruction in the Dockerfile, which is used to build the image. When an image is built, each instruction in the Dockerfile creates a new layer in the image.

Each layer is a snapshot of the file system at a specific point in time. When a change is made to the file system, a new layer is created that contains the changes. This allows Docker to use the layers efficiently, by only storing the changes made in each layer, rather than storing an entire copy of the file system at each point in time.

Layers are stacked on top of each other to form a complete image. When a container is created from an image, the layers are combined to create a single, unified file system for the container.

The use of layers allows Docker to create images and containers efficiently, by only storing the changes made in each layer, rather than storing an entire copy of the file system at each point in time. It also allows Docker to share common layers between different images, saving space and reducing the size of the overall image.

Some important Docker commands:
– Here are some common Docker commands:
– docker build: Build an image from a Dockerfile
– docker run: Run a container from an image
– docker ps: List running containers
– docker stop: Stop a running container
– docker rm: Remove a stopped container
– docker rmi: Remove an image
– docker pull: Pull an image from a registry
– docker push: Push an image to a registry
– docker exec: Run a command in a running container
– docker logs: View the logs of a running container
– docker system prune: Remove unused containers, images, and networks
– docker tag: Tag an image with a repository name and tag

There are many other Docker commands available, and you can learn more about them by referring to the Docker documentation.

How to Dockerize a simple application?
Now, coming to the root cause of all the explanations stated above, how we can dockerize an application.

First, you need to create a simple Node.js application and then go for Dockerfile, Docker Image and finalize the Docker container for the application.

You need to install Docker on your device and even check and follow the official documentation on your device. To initiate the installation of Docker, you should use an Ubuntu instance. You can use Oracle Virtual Box to set up a virtual Linux instance for that case if you don’t have one already.

Caveat Emptor
Docker containers simplify the API system at runtime; this comes along with the caveat of increased complexity in arranging up containers.

One of the most significant caveats here is Docker and understanding the concern of the system. Many developers treat Docker as a platform for development rather than an excellent optimization and streamlining tool.

The developers would be better off adopting Platform-as-a-Service (PaaS) systems rather than managing the minutia of self-hosted and managed virtual or logical servers.

Benefits of using Docker for Development and Operations:

• Docker is being talked about, and the adoption rate is also quite catchy for some good reason. There are some reasons to get stuck with Docker; we’ll see three: consistency, speed, and isolation. 
• By consistency here, we mean that Docker provides a consistent environment for your application through production. 
• If we discuss speed here, you can rapidly run a new process on a server, as the image is preconfigured and is already installed with the process you want it to run.
• By default, the Docker container is isolated from the network, the file system, and other running processes.

Docker’s layered file system is one in which Docker tends to add a new layer every time we make a change. As a result, file system layers are cached by reducing repetitive steps during building Docker. Each Docker image is a combination of layers that adds up the layer on every successive change of adding to the picture.

The Final Words
Docker is not hard to learn, and it’s easy to play and learn. If you ever face any challenges regarding application development, you should consult 9series for docker professional services.

Source : 9series