Docker

What is Docker? The spark for the container revolution

Docker is an open-source tool to efficiently create lightweight, portable, self-dependent containers for any software. It gives developers and software teams the standard toolbox that they use to take advantage of the distributed software applications. Docker is the best way to run software inside containers. Due to its numerous powerful feature, it is very attractive for developers. This Docker tutorial will be a short introduction to how to work with Docker. 

What is Docker?

Docker is an open-source tool for development teams and individuals to build, deploy, and run distributed software applications. It is a tool that permits you to run software applications in containers. Containers are a way of packaging up software with all its dependencies in a single package. It implies that we can deploy the application anywhere and can run it easily on a machine that has Docker installed. Click Here to Download

If you’ve used virtual machines before, Docker containers are like lightweight VMs. You can run more of them on a single host machine than you can virtual machines. And, unlike VMs, Docker containers share the kernel with the host operating system, so there’s no overhead involved when switching between your containerized app and other applications running on the host.

Trying to explain what Docker is, I’ve come across metaphors that help me understand it better:

  • The first is to think of each Docker container as a self-sufficient mini-computer or VM that runs one application and nothing else. Each one can be created in seconds, each one runs on just a few MBs of storage, and each one is isolated from other containers.
  • Once you have a container for an application, you can move it around from server to server and even from cloud to cloud (or back) without worrying about dependencies or configurations because everything needed to run your app is already included as part of the image.

Docker allows applications to fastly converge from components and remove the friction between the development team, Quality Assurance, and operational environments. As an outcome, IT can deploy quickly and run the identical application, without change, on all devices includes laptops, data center VMs, and any cloud. It is also a tool allowing system administrators to deploy their application services in the same consistent fashion across all environments, including development, testing, and production.

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History of Docker 

Docker was created and open-sourced by Solomon Hykes in 2013. The goal was to enable developers to build and run their applications in containers, which are similar to virtual machines but are more lightweight, share the same operating system, and isolate applications from each other.

In August 2014, Docker became popular with the development of a new technology called “microservices,” which is a type of architecture where large software programs are broken down into small parts that can be developed separately. The small parts then work together to create the finished product. Google adopted Docker in 2015 to help it solve its own problems with microservices architecture. Today Docker is used by many technology giants like Twitter, Spotify, and eBay.

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Why use Docker?

Docker allows us to package a software application with all of its dependencies into a standard unit for software development. For example, you can create a Docker container with the Linux operating system, Apache web server, and MySQL database already installed. This allows developers to quickly launch pre-configured applications on their own machines. It also helps with collaboration because teams can share containers over the Internet without having to worry about different environments affecting each other.

The best thing about Docker is that it’s an open platform that most cloud providers support. You can use the same Docker toolset from any cloud service provider, including Amazon Web Services, Google Cloud Platform, and Microsoft Azure. One of the reasons why this works well is because Docker uses open source standards like the Open Container Initiative (OCI).

You can do all of the following with Docker:

  • Build any app in any language using any toolchain.
  • We can deploy application it to any infrastructure and run it virtually anywhere.
  • Make use of Linux container technologies like cgroups and namespaces
  • Isolate apps from each other and from the host system
  • Docker Compose: Docker Compose is a tool for defining and running multi-container Docker applications. With Docker Compose, we can express a multi-container software application in a single file, and after that, we can spin the application up with a single command that does everything to deploy and run the application.
  • Private Registry: A secure place to store your applications and images.
  • Launch Containers: Docker provides a simple interface to run containers.
  • Share Files: Use the file sharing Docker driver to mount local directories into containers.
  • Increase in speed of software delivery, since there is no need to wait for installation time.
  • Saving time and money on administration and maintenance of development machines.
  • More efficient usage of cloud computing resources (if used with some cloud orchestration tool like docker swarm).

Docker Terms and Technologies

What is Docker Container?

Docker Container

Containerization is a technology invented by Google. It creates individual units of software called containers. Containers are like shipping containers in that they are identical and can be stacked on top of each other. This makes it possible to ship your application from one computer to another as easily as if you were moving shipping containers at a port.

Docker container covers up a component of application in a whole filesystem that includes everything that it requires to run e.g: code, runtime, system tools, system libraries – anything you can configure on a server. This implies that the application will run in the same way regardless of the environment it is running. This is useful for two reasons: 

  • It makes it easy to create an exact copy of your production environment for testing and staging purposes
  • It allows developers to work in isolation, without access to the system tools or packages installed on the computer they are using.

What is Docker Engine?

The Docker Engine is a container tool that enables you to package your software application with all of its dependencies into a standard unit for product development. It is built on top of the Linux Kernel and comes with a command-line interface (CLI) tool called ‘docker’. Docker Engine lets you deploy any application as a lightweight, portable virtual container that includes its own filesystem, process space, network interfaces, and so on.

What is Docker Compose?

Docker Compose is a tool for defining and running multi-container Docker applications. With Compose, you define a multi-container application in a single file, then spin your application up with a single docker-compose up command. The docker-compose.yml file is where you configure your application’s services. By default it uses the Dockerfile from the current directory, so you can build an image, run docker-compose up and have your app start in one go!

What is Dockerfile?

Dockerfile

A Dockerfile is a text document that contains a collection of instructions for Docker to use when building an image. The instructions can be anything and can be written in any language. The instructions are processed by the Docker engine which then creates an image based on the instructions in the Dockerfile. These instructions can be used to create a Docker image from scratch or mostly from pre-existing images.

What is Docker Image?

Docker image is just a file that describes the environment in which your application will run. A Docker image file is a template for creating containers. It’s read-only, so you’ll need to create or copy a container before you can start working with it. All the files that make up an application are placed into a Docker image, along with some additional information about how those files should be assembled and what environment variables should be set when the container is created.

What is Docker Hub?

Docker Hub is a cloud service that allows you to easily share your distributed applications with others and manage them more effectively. It includes services such as repositories, automated builds, user management, security and more. All images uploaded to Docker Hub are publicly visible and accessible. This includes all images in the private repositories you may have. Docker Hub is integrated with other Docker tools, so you can push and pull images directly from the Docker CLI or the Docker Compose tool without ever leaving the command line.

Docker Hub provides many functionalities:

  • Manage your own repositories with tags, branches and more.
  • Collaborate with other users on repositories.
  • Add automated builds to your repositories.
  • Automatically build and publish your applications as images if you push code to a repository.

What is Docker Run Utility?

The Docker Run Utility (aka docker-compose ) is a tool that manages your containers. For example, you can create a container with a web application, a database, and some cron jobs, or even all of them at once. You can also create as many containers as you want. Docker provides an interface to describe what is inside and how they interact with each other.

What is Docker Desktop?

Docker Desktop is a comprehensive software development environment that contains everything you require to build, deploy and run distributed software applications. It combines Docker Swarm, Docker Compose, Docker Machine, and other tools into a single desktop application. You can use it on your Mac or Windows computer.

Docker Architecture. How Docker works?

Docker Architecture. How Docker works

Docker is one of the best solutions today to the problem of packaging and distributing applications. It permits you to package an application with its entire dependencies into a complete unit that incorporates everything it requires to deploy and run on any machine.

This standardized unit can then be distributed easily and run on any machine capable of running Docker containers. These units are much easier to distribute than individual applications and their dependencies separately. In addition, they take advantage of the inherent characteristics of Linux containers.

Taken together, these benefits make Docker images the perfect building blocks for modern server environments. The Docker platform provides a complete solution for developers and system administrators alike that allows them to define, ship, and run any application as a lightweight container.

Docker automates the entire application lifecycle, so IT departments can ship applications faster while spending less time on error-prone, repetitive tasks. The Docker Engine runs any application in isolation, making it lighter and easier to move around, while the Docker Hub cloud service makes it simple to find, distribute, and deploy components of applications. The idea is that you can take your application and everything it needs to run (all the libraries and dependencies and so on) and ship it all out as one little container. Then you can put it on a computer anywhere, even one halfway around the world.

Docker Advantages 

Following are the advantages of docker:

  1. Quick installation: You can run Docker on Linux distributions as well as on Windows 10. And you can quickly install it on any existing server or laptop that runs Linux by using an installation script.
  2. Tiny size: The entire base image is just 50MB. This makes the download and deployment of Docker containers lightning fast.
  3. Easy to use: Setting up new containers is a simple process and doesn’t require very much expertise.
  4. Built-in security: Since Docker containers are isolated from each other, they don’t pose a threat to your system’s security like other virtualization software such as VirtualBox and VMware do.
  5. Lightweight nature: The lightweight nature of the software means you can run more than one container simultaneously on your machine without causing a slowdown in performance or resource usage.
  6. Supports various applications: It supports different programming languages, that includes Java, Ruby, Node.js, and Python, among others, thereby making it possible for developers to build multi-tiered applications easily.
  7. Easier scalabilit: Docker’s lightweight nature makes it ideal for creating clusters of identical machines with minimal effort, which facilitates fast scaling. This also means that you’re able to use fewer machines, as you’re able to build more efficient systems overall.

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Docker Disadvantages

Docker is a powerful tool that has many advantages, but it also has some disadvantages that are described below:

  1. Tight coupling: Docker uses “tight coupling”, which means that all the services you need to run an application must be on the same machine, or they will fail. This is because Docker requires the application to live inside a container, which runs on top of one or more OSs. If the application needs a service that isn’t included with any of these OSs, then it won’t work correctly.
  2. Large Container Size: The Docker container size is huge, if you need to develop applications that work on the local machine, then Docker containers will take up too much space – It’s nice to have all the dependencies which are required for your development environment in one place, but it isn’t practical if you are working on machines with limited hard drive space.

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What is Docker Today? 

Docker has gained a lot of popularity since its first release in March 2013. It became the de facto standard for application containerization, and it has become so popular that many companies started to switch their infrastructure to Docker, leading to the creation of specialized tools that make migration easier.

Till now, we were able to argue that containers were not ready for the enterprise. But today is a different story. We have mature orchestration systems like Kubernetes, Mesos, and Swarm, and we have specialized tools such as Rancher and Habitat. These tools are not just easy to use; they also offer great flexibility that allows us to build a wide range of infrastructure services. Therefore, we can now feel confident about using Docker for development and production alike.

Conclusion

Docker is a great tool to help you build and deploy micro-services. Now, with Docker, you can easily make sure that your app will work on any host, on any environment, on any cloud or infrastructure. It’s a lightweight container solution for an independent developer.

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