Docker vs. Kubernetes: What is the difference?

Kubernetes and Docker are the 2 names we hear more and more these days, they are both known as a container orchestration solution. However, “Kubernetes vs. Docker” is also a somewhat misleading phrase, because Kubernetes and Docker aren’t direct competitors. Instead, if you look a little closer, you’ll find that the technologies operate at different layers of the stack, and can even be used together.

Understanding both Docker and Kubernetes is essential if you want to build and run a modern cloud infrastructure. Let’s take a look to see how they both fit into the world of linux containers, and how you can use them when architecture your own applications.

What is a container?

A container is a standard unit of software that packages up the code and all its dependencies so the application runs quickly and reliably from one computing environment to another.

What makes it special is that when you run a container, you know exactly how it will run – it’s predictable, repeatable and immutable. There are no unexpected errors when you move it to a new machine, or between environments.

All of your application’s code, libraries, and dependencies are packed together in the container as an immutable artifact. You can think of running a container like running a virtual machine, without the overhead of spinning up an entire operating system. For this reason, bundling your application in a container vs. a virtual machine will improve startup time significantly.

The above characteristics make containers an awesome tool and essential building block in modern cloud architecture. This all sounds really nice, but how do you actually build a container?

The Rise of Containerization and Docker

Docker is currently the most popular container platform. It’s an open source collection of tools that help you “Build, Ship, and Run any App, Anywhere”. Yes, it really is as magic as it sounds.

Although the idea of isolating environments dates quite far back, and there has been other container software in the past, Docker appeared on the market at the right time and was open source from the beginning, which likely led to its current market domination.

With Docker, you create a special file called a Dockerfile. Dockerfiles define a build process, which, when fed to the ‘docker build’ command, will produce an immutable docker image. You can think of this as a snapshot of your application, ready to be brought to life at any time. When you want to start it up, just use the ‘docker run’ command to run it anywhere the docker daemon is supported and running. It can be on your laptop, your production server in the cloud, or on a raspberry pi. Regardless of where your image is running, it will behave the same way.

Docker also provides a cloud-based repository called Docker Hub. You can think of it like GitHub for Docker Images. You can use Docker Hub to store and distribute the container images you build.

Role of Orchestration Systems

While Docker provided an open standard for packaging and distributing containerized applications, there arose a new problem. How would all of these containers be coordinated and scheduled? How do all the different containers in your application communicate with each other? How can container instances be scaled?

Solutions for orchestrating containers soon emerged. Kubernetes, Mesos, and Docker Swarm are some of the more popular options for providing an abstraction to make a cluster of machines behave like one big machine, which is vital in a large-scale environment.

When most people talk about “Kubernetes vs. Docker,” what they really mean is “Kubernetes vs. Docker Swarm.” The latter is Docker’s own native clustering solution for Docker containers, which has the advantage of being tightly integrated into the ecosystem of Docker, and uses its own API. Like most schedulers, Docker Swarm provides a way to administer a large number of containers spread across clusters of servers. Its filtering and scheduling system enables the selection of optimal nodes in a cluster to deploy containers.

Kubernetes is the container orchestrator that was developed at Google which has been donated to the CNCF and is now open source. It has the advantage of leveraging Google’s years of expertise in container management. It is a comprehensive system for automating deployment, scheduling and scaling of containerized applications, and supports many containerization tools such as Docker.

For now, Kubernetes is the market leader and the standardized means of orchestrating containers and deploying distributed applications. Kubernetes can be run on a public cloud service or on-premises, is highly modular, open source, and has a vibrant community. Companies of all sizes are investing into it, and many cloud providers offer Kubernetes as a service. Sumo Logic provides support for all orchestration technologies, including Kubernetes-powered applications.

Manage Docker Containers with Kubernetes

Once you’ve recovered from the excitement of spinning up your first few Docker containers, you’ll realize that something is missing. If you want to run multiple containers across multiple machines – which you’ll need to do if you’re using microservices – there is still a lot of work left to do.

You need to start the right containers at the right time, figure out how they can talk to each other, handle storage considerations, and deal with failed containers or hardware. Doing all of this manually would be a nightmare. Luckily, that’s where Kubernetes comes in.

Kubernetes is an open source container orchestration platform, allowing large numbers of containers to work together in harmony, reducing operational burden. It helps with things like:

  • Running containers across many different machines
  • Scaling up or down by adding or removing containers when demand changes
  • Keeping storage consistent with multiple instances of an application
  • Distributing load between the containers Launching new containers on different machines if something fails.

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