What Is Docker and How Does It Work? – Docker Explained

If you have an application or service and want it to work on different systems like VPSs or dedicated machines without any issues, consider using containers. One of the most popular container platforms is Docker, although not everyone knows what it is and how it works.

In this tutorial, we’ll explain what Docker is, how it works, and how it differs from virtual machines (VMs) and systems, like Kubernetes and Jenkins. We’ll also go through the pros and cons of Docker and list its most popular use cases.

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Docker vs Virtual Machine

While Docker and virtual machines serve a similar purpose, their performance, OS support, and portability differ significantly.

The main difference is that Docker containers share the host’s operating system, while virtual machines also have a guest operating system running on top of the host system. This method of operation affects the performance, hardware needs, and OS support. Check the table below for an in-depth comparison.

	Docker	Virtual Machine
OS	Shared OS between containers	New OS for each VM
Security	Less secure because the operating system and kernel are shared	More secure as VMs don’t share the operating system
Performance	Fast performance even with several containers	More virtual machines equal less stable performance
Boot-up time	Fast (seconds)	Slow (minutes)
Memory needs	Lightweight	Require a lot of memory
Storage needs	Usually megabytes	Usually gigabytes
Portability	Easy to deploy in different environments	Hard to port a VM to another system

Even though Docker’s container technology comes on top in most aspects, virtual machines are more secure because the OS is kept independent from the hardware.

Docker vs Kubernetes and Jenkins

In the following section, we’ll discuss how Docker stacks up against Kubernetes and Jenkins and explain the differences between them.

Comparing Kubernetes With Docker

While Docker is a platform for building and running containers, Kubernetes is an open-source container orchestration system. These two systems cannot be compared directly – Docker is responsible for creating containers, and Kubernetes manages them at a great scale.

However, Docker offers its own orchestration system called Docker Swarm. Here’s a table with a comparison of Kubernetes and Docker Swarm:

	Kubernetes	Docker Swarm
Installation	Difficult and long	Easy and fast
Scalability	Automatic scaling	Offers no scaling
Cluster creation	Easy	Difficult
Load balancing	Manual	Automatic
Monitoring	Built-in monitoring tools	Only supports third-party monitoring tools

Comparing Docker With Jenkins

It is not possible to compare Jenkins with Docker because they are products that serve entirely different purposes.

Jenkins is a core automation system for the CI/CD (continuous integration and continuous delivery) development model where developers push small chunks of code continuously to prevent merge errors. Docker, on the other hand, is a containerization system.

While these systems cannot be compared, you can use both for the best results. Have Jenkins schedule different tasks and Docker isolate jobs from one another with the help of containers.

Understanding Docker Containers

Using Docker containers saves users the hassle of troubleshooting possible compatibility issues between systems. That’s because with Docker, a piece of software runs the same in all environments.

What Is a Docker Container?

A Docker container is a software package with all the required dependencies to run a specific application. All of the configuration and instructions to start or stop containers are dictated by the Docker image. Whenever a user runs an image, a new container is created.

It’s easy to manage containers with the help of the Docker API or command-line interface (CLI). If multiple containers are required, users can control them with the Docker compose tool.

How Does Docker Work?

The Docker architecture consists of four main components along with Docker containers which we’ve covered earlier.

• Docker client – the main component to create, manage, and run containerized applications. The Docker client is the primary method of controlling the Docker server via a CLI like Command Prompt (Windows) or Terminal (macOS, Linux).
• Docker server – also known as the Docker daemon. It waits for REST API requests made by the Docker client and manages images and containers.
• Docker images – instruct the Docker server with the requirements on how to create a Docker container. Images can be downloaded from websites like Docker Hub. Creating a custom image is also possible – to do it, users need to create a Dockerfile and pass it to the server. It’s worth noting that Docker doesn’t clear any unused images, so users need to delete image data themselves before there’s too much of it.
• Docker registry – an open-source server-side application used to host and distribute Docker images. The registry is extra useful to store images locally and maintain complete control over them. Alternatively, users can access the aforementioned Docker Hub – the world’s largest repository of Docker images.

The Pros and Cons of Docker

While Docker has many advantages, it does fall short in some respects. In this section, we’ll go over the main pros and cons of the software.

Docker Advantages

• Portability – the main appeal of Docker is its portability. It allows users to make or install a complex application on a machine and be sure that it will work on it. Docker containers include everything that an application needs with little to no input from the user.
• Automation – with the help of cron jobs and Docker containers, users can automate their work easily. Automation helps developers avoid tedious and repetitive tasks as well as save time.
• Community – Docker has a dedicated Slack channel, community forum, and thousands of contributors on developer websites like StackOverflow. What’s more, there are over 9 million container images hosted on Docker Hub.

Docker Drawbacks

• Speed – even though running an app via a Docker container is faster than doing so on a virtual machine, it is still considerably slower than running applications natively on a physical server.
• Ease of use – Docker is not meant to run applications that require a graphical user interface (GUI). This means that users need to be familiar with the command line and perform all actions there. The steep learning curve, OS-specific caveats, and frequent updates make mastering Docker challenging. Even if you feel that you know Docker inside out, there is still orchestration to consider, adding another level of complexity.
• Security – Docker runs on the host’s operating system. This means that any malicious software hidden in containers may find its way to the host machine.

Docker Use Cases

Docker has a wide range of applications. In this section, we’ll go over three common Docker use cases and explain how you can benefit from it.

To Try New Software

With Docker, you can try out new software without installing it manually. Docker is also useful if you need to have a piece of software ready quickly. For example, setting up a MySQL server is a long and tedious process. With Docker, it only takes one command via the CLI to do it.

To Learn About the CLI

Even though Docker can run on all types of machines, it was primarily designed for Linux. Therefore, we recommend setting it up on a Linux-based system. It will provide you with an excellent opportunity to learn more about system administration, command-line interface, and scripting.

To Reduce Incident Risk

In case of hardware failure, users can quickly revert any changes if they have a Docker image ready. They only need to import the image backup to a new machine, and Docker will do the rest. Docker image backups are also beneficial when developers want to roll back to a previous version of specific software due to bugs or incompatibility.

Conclusion

Developing an application is a challenge, and making sure that it works in every environment is an even bigger milestone. Docker containers solve this issue by giving developers a way to port software easily.

In this article, we’ve gone over the differences between virtual machines and Docker, explained how it works, and compared it to popular systems like Kubernetes and Jenkins. We’ve also discussed Docker’s pros and cons and covered some of its use cases.

We hope that this article has helped you to learn more about Docker. If you have any questions or suggestions, let us know in the comments section below.

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