What is Docker? How Docker Works and Its Architecture

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Docker was founded by Solomon Hykes and Sebastien Pahl in 2010 and launched in 2011. It is an open-source platform that uses OS-level virtualization to build software. These software packages are delivered in packages called containers.

What is Docker?

Containers are created for automating the deployment of applications and are also portable and can run on the cloud or on-premises. It enables programmers to pack applications and all their dependencies into a single container, making it simple and safe to build, deploy, manage, and update them.

These containers have application-specific libraries and binaries, ensuring fast and seamless application work in any environment. Using Docker containers, developers can set up many instances of Jenkins, Puppet, and more that can all run either in the same container or in different containers.

These instances can also interact with one another through well-defined channels by running just a few commands. Ben Lloyd Pearson has rightly written in “Opensource.com” that Docker has been designed in a way it can easily be incorporated into DevOps applications such as Puppet, Chef, Vagrant, and much more. He further states that Docker can be used on its own to manage and build development environments.

Why Should One Choose Docker

By utilizing it, standardized executable components including application source code, operating system libraries, and other dependencies can be packaged into a single container without wasting or blocking host resources.

Containers are handled by the containerization engine. In comparison to virtual machines, it uses the host operating system and shares the relevant libraries, and it takes less time to start its work.

It offers all the services offered by VMs but provides an additional layer of abstraction at the OS-level for gaining extra benefits like:

  • Lightweight—Unlike virtual machines (VM), a container does not carry the entire payload of an OS but only the necessary parts and relevant dependencies that are required to execute the code, thus making it simple, fast, and lightweight to use. 

Unlike VMs, where the guest OS needs to start from the starting point, containers work on the host OS, saving precious boot-up time. Developers can choose from Windows, Linux, and many more operating systems for their development environments with Dockers.

  • Resource Efficiency: Using containers, one can run many copies of the application on the same platform. It uses shared operating systems. For example, containers rest on top of a single Linux instance, leaving behind 99% of the junk on which the virtual machine relies. Also, full virtualization requires more resources than containerization, thus ensuring optimal use of resources.
  • Increased Productivity – It is easy to access, deploy, and restart. Support for continuous integration and continuous delivery (CI/CD) pipelines is one of the benefits of using these. It integrates the code into a shared repository for faster code deployability.
  • Container Reusability: Containers can be reused as many times as one wants and, therefore, can be used as basic templates for building new containers. It can also automatically create a new container based on the application source code.
  • Versioning of the Container—Easily monitors different versions of a container, tracking down who and how a container was built. It easily updates the container image and can even roll back to the previous one without any complexity. Thus, restoration to the previous versions is easy while using Docker.
  • Docker Enterprise Edition (EE): Enterprise Edition (EE) is another feature provided by Docker that is designed for enterprise development and is used to run large business tools.

In addition to the benefits listed above, it is important to keep in mind that Docker containers can run anywhere on a variety of platforms, including different operating systems, different locations, Azure, the cloud, and customer data centers, among others.

Additionally, Docker images may operate natively on Linux and Windows by utilizing straightforward commands and labor-saving automation.

Learn these terms before you start using Docker

Before getting started with Docker, you should know some basic terms and tools. While using Docker, we must know the following terms and tools:

1. Docker Files

Every Docker container starts with a simple text file called “Docker File” that contains instructions guiding us to build the Docker container image. These files are a list of commands that Docker Engine will run to assemble the image and automate the process of Docker image creation.

2. Docker Images

It contains executable application source code and essentially all the dependencies that the application needs to run securely. Using these Images, single or multiple instances of the container can be created as per the requirement of the programmer.

Users can build Docker images from scratch or use the common repository and customize them as per their choice. Multiple images can be created from a common base and then customized differently. Also, multiple images can share common commonalities in their stack.

3. Docker Container

It runs instances of Docker images. While Docker images are read-only, they are executable content. The user interacts with these and adjusts them as per the demands.

Changes like the addition and deletion of files are common and saved to the container layer only. With the help of these containers, applications can run virtually anywhere and are portable.

4. Docker Hub

The Docker Hub is a repository for all the Docker images and acts as the largest library, holding over 100,000 Docker images. All the Docker hub users can share their images at will and can also download pre-defined different base images and work on them. These downloaded base images act as a starting point for their to-be-designed projects.

Architecture and workings of Docker

The Docker engine is an application that is installed on a host machine. It works on the client-server model, leveraging a server, which is a long-running program called a Daemon process, and a client which is a user command-line interface (CLI).

Application program interfaces (API) are used for server and client interaction. Containers are executed by passing commands from a CLI client to the server Docker daemon. To build a Docker image, the CLI client issues a command to the Docker Daemon and based on user inputs, the daemon will build an image which is then stored on Docker Hub or some local repository.

The CLI can also instruct the daemon to retrieve an image that has already been saved to the Docker Hub and was created by a different user in order to customize it to his/her needs. Finally, if a developer wants a running instance of a Docker image, a run command can be issued from the CLI, which will create a container.

How to Get Started?

For a few containers, it is comparatively very simple and easy to use. Application management is done within the Docker Engine itself. But for applications that require thousands of images, containers, and hundreds of services, management will not be easy without purpose-built tools.

To build an application that uses different processes from different containers that all reside on the same host, ItCompose is required to manage the application’s architecture.

It creates a file—YAML—that specifies which services are to be included in a container, making it a single command job to manage all the container files and easy deployment of the application. Persistent volumes of storage can be defined, base nodes and documents can be specified, and service dependencies can be easily configured using the same.

For complex tasks, containers can be monitored using container orchestration tools. While it has an in-built orchestration tool named Docker Swarm, many of the developers choose Kubernetes instead.

Kubernetes is an open-source container developed by Google that schedules processes and automates different tasks that are integral to the management of application architectures.

Kubernetes provides several services, including container deployment and updates, service discovery, storage provisioning, and load balancing. Platform-as-a-Service (PaaS) tools like Istio and Knative for Kubernetes enable organizations to deploy high-productivity containerized applications.

More to Know

Using it, more apps can be made to run on the old servers, and it also gives the advantage of easy packaging and shipping of programs. According to a report by Docker, more than 3.5 million applications have been placed in containers and over 37 billion have been downloaded.

As per the Puppet survey of 4,600 IT professionals, information technology departments using strong DevOps deployed software at a 200 times faster rate and recovered 24 times faster in comparison to other IT departments. Besides, the failure rate is three times lower, which provides greater security with less time consumption on unplanned work.

Almost all cloud companies have adopted Docker. DataDog (a cloud-monitoring system) reported in 2016 that about 13.6% of its customers have adopted it. Linux powers like Red Hat and Canonical have embraced Docker too.

Companies like Microsoft, Amazon, and Oracle have started to rely on Docker. Today, the top 5 companies that use Docker are JPMorgan Chase, ThoughtWorks, Inc., Docker, Inc., Neudesic, and SLALOM, LLC. It has started to work on more than 20 hosts now.

The Verdict

It enable users to isolate different codes into different containers thus, providing a feature where mega, complex projects can be divided into simple goal-oriented multiple tasks that breaks down the complexity and increases the overall efficiency.

The most common types of images that are being used these days are:

  • NGINX – deploy and run HTTP servers.
  • Redis – used as an in-memory database, message queue, or cache, and
  • Postgres – open-source relational database.

Developers can also run test suites to test the changes applied to the code in the containers instantly as soon as they make the changes and optimize its functionality.

Putting all of it together, it will not be wrong to state that Docker is a more sensible option than virtual machines or other technologies that make managing and deploying applications much easier for the developer.

Frequently Ask Questions

1. Does Docker work with Windows, Linux, and Mac OS X?

Programs and executables for Linux and Windows can both execute in Docker containers. Linux (on x86-64, ARM, and many more CPU architectures) and Windows both natively support the Docker platform (x86-64).

The products made by Docker Inc. enable you to create and execute containers on Linux, Windows, and macOS.

2. Does the container’s leaving cause me to lose my data?

That’s not the case! As long as you do not specifically erase the container, any data that your program writes to disc remains there. It is still possible to access the file system of the container even when the container halts.

3. How large can you scale Docker containers?

Today, container technology is used in some of the biggest server farms in the world. Large online deployments like Google and Twitter, as well as platform providers like Heroku, use container technology at scales of hundreds of thousands or even millions of containers.

4. How do I link Docker containers together?

Right now, using Docker’s network functionality to link containers is advised. You may see specifics on using Docker networks.

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