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.

Download Complete Linux Commands Cheat Sheet


Docker is open-source software used to deploy applications inside virtual containers. Containerization allows various applications to work within different complex environments. For example, Docker allows running the WordPress content management system on Windows, Linux, and macOS systems without any issues.

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.

DockerVirtual Machine
OSShared OS between containersNew OS for each VM
SecurityLess secure because the operating system and kernel are sharedMore secure as VMs don’t share the operating system
PerformanceFast performance even with several containersMore virtual machines equal less stable performance
Boot-up timeFast (seconds)Slow (minutes)
Memory needsLightweightRequire a lot of memory
Storage needsUsually megabytesUsually gigabytes
PortabilityEasy to deploy in different environmentsHard 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

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:

KubernetesDocker Swarm
InstallationDifficult and longEasy and fast
ScalabilityAutomatic scalingOffers no scaling
Cluster creationEasyDifficult
Load balancingManualAutomatic
MonitoringBuilt-in monitoring toolsOnly supports third-party monitoring tools

Comparing Docker With Jenkins

It is not possible to compare Jenkins with Docker because they 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.

Expert Tip


Using Docker on Hostinger is as easy as getting a VPS and installing it on your Linux distribution like Ubuntu or CentOS.

Editor

Mantas Staniulis

Site Availability Engineer

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.

Expert Tip

Don’t download Docker images from unknown sources as they could contain malware.

Editor

Egidijus Navardauskas

Head of Cyber Security

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.

What Is Docker FAQ

Docker vs Docker Engine

Docker is the name of the platform, while Docker Engine is an open-source container technology that consists of a Docker server (daemon), client, and APIs. People might also confuse the software with the Docker client because it’s also called docker, only in lowercase letters.

Docker Community Edition vs Enterprise Edition

Docker CE and EE are two different versions of Docker – the main difference is that the former is free, while the latter is a premium service. It’s worth noting that both offer the same core features and functionality but work on different OSs. If you’re not creating software at a great scale, we recommend opting for the CE.

Is Docker Hard to Learn?

It can take a while to master Docker, although launching your first container won’t take long. To get started, Docker provides its users with an easy-to-use Docker Desktop application and offers comprehensive documentation for beginners and intermediate users.

Was this tutorial helpful?

Author
The author

Ignas Rimkūnas

Ignas is a Technical Content Writer at Hostinger. After helping people tackle even the most complex technical issues as a Customer Success Specialist, his current goal is to write easy-to-follow articles so that these issues will not happen at all. During his free time, Ignas likes to play video games and fix up things around his house.