Containers and microservices have become the darling technology of enterprise businesses. This is especially true if your company has adopted CI/CD and DevOps solutions or is looking to become more agile in a world of ever-growing competition.
When you look toward the world of containerization, Kubernetes and Docker rise to the top. Although these DevOps tools are on different trajectories, they are both front and center of the containerization trend, and it’s very likely you have, are or will use one or both of them.
Containers benefit companies by providing:
- Agile application development and deployment
- CI/CD
- DevOps software
- Observability
- Cloud and OS portability
- Application-centric management
- True resource isolation
Between Kubernetes and Docker, which of these DevOps tools is best suited to meet the needs of your company and your DevOps workflow? Let’s find out.
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What is Kubernetes?
Kubernetes is an open-source container orchestration platform that makes it possible to manage, automate and scale your containerized applications and microservices. Kubernetes was originally designed by Google and is now maintained by the Cloud Native Computing Foundation.
Kubernetes is all about orchestrating large containerized deployments and not just one-off containers. Kubernetes can be deployed on a cluster of bare metal servers in your data center or on third-party cloud providers and works with a controller to manage the resources of nodes joined to the cluster. A cluster can consist of a controller and one node or a controller and up to 5,000 nodes, although it’s not optimized to handle more than 500 nodes per cluster.
Once upon a time, Kubernetes used Docker as its runtime engine. That is no longer the case, and instead Kubernetes supports the likes of the Podman and containerd runtime engines.
What is Docker?
Although the purpose of Docker is similar to that of Kubernetes, these two DevOps tools are quite different. Whereas Kubernetes focuses on large-scale deployments, Docker is just as content deploying a single container to your network. That doesn’t mean Docker cannot work with larger deployments. Thanks to Swarm mode, it is possible to deploy a cluster of Docker nodes and deploy your containerized applications and microservices at scale.
One important aspect of Docker is that it offers a far lower learning curve than Kubernetes. Anyone looking to jump into the world of containers would do well to start with Docker and work their way up to Kubernetes. And even though the DevOps tools list is quite vast, these two technologies are two of the most important.
Head-to-head comparison: Kubernetes and Docker
Container management
Both Kubernetes and Docker are used to deploy and manage containers. Kubernetes, by default, works as a cluster of nodes where the containerized application can be scaled as needed. Docker, on the other hand, is a container runtime engine that is as at home deploying a single container to a single node as it is deploying full-stack applications to a cluster (called a Docker Swarm).
The primary focus on Docker is developing, sharing and running individual containers, whereas Kubernetes is focused on containerized applications at scale.
Controllers and nodes
Although Docker doesn’t require the deployment of both controllers and nodes, if you plan on using Docker Swarm, you will have to use both a controller and multiple nodes.
Kubernetes, on the other hand, does require the use of both controllers and nodes. These controllers and nodes can be off-the-shelf servers in your data center or hosted by third-party cloud vendors, such as AWS, Azure, Google Cloud, Rackspace and Linode.
Developer tools
Kubernetes and Docker contain all the tools you need to develop your containerized applications. Both depend on image registries (such as those hosted on the likes of Docker Hub) and use JSON-formatted manifests to layout portable, containerized applications. Both offer command-line interface tools for development, as well as several third-party GUI tools.
Kubernetes and Docker can be integrated into your current development tools, such as your favorite IDEs and versioning systems such as git.
Clusters
both Kubernetes and Docker can make use of clusters. The difference is that Kubernetes requires a cluster, whereas a Docker Swarm is optional. This also highlights the biggest difference between Kubernetes and Docker: Kubernetes scales far easier and larger than Docker.
Persistent volumes
When you deploy a containerized application, chances are high that it’s going to depend on saved data. Thankfully, both Kubernetes and Docker can make use of persistent volumes. These volumes save data outside of the container such that, should something happen to the running containers, the data is saved in its own persistent volume.
Persistent volumes also make it possible to share data between containers. For example, you could deploy a MySQL container using a persistent volume and have multiple containers connect to that database.
Containers and pods
Docker deploys containers, which are containerized applications and microservices. Kubernetes, on the other hand, actually wraps containers into pods, which are a higher-level structure that can contain multiple containers sharing the same resources. One should use caution not to deploy too many containers to a single pod, as those containers must scale together, which could lead to wasted resources.
Although Docker doesn’t work with pods, it is possible to deploy full-stack applications by way of individual but interconnected containers.
Networking
One area where Docker really shines is in networking. You can easily deploy a container with Docker and have it immediately and easily accessed from a network.
Kubernetes isolates pods from the outside world. Because of this, you must add an Ingress controller or LoadBalancer to access those containerized applications from outside the cluster.
Feature comparison: Kubernetes vs. Docker
| Feature | Kubernetes | Docker |
|---|---|---|
| Installation | Challenging | Simple |
| Learning curve | Steep | Shallow |
| Scaling | Automatic | Manual |
| Monitoring | Built-in | Requires third-party tools |
| Load balancing | Manual | Automatic |
| CLI tools | Built-in | Built-in |
| Runtime engine | Requires third-party tools | Built-in |
| Clustering | Built-in | Must be deployed in cluster mode (Docker Swarm) |
| Recommended node size | Up to 500 nodes | Recommended max of seven manager nodes for a swarm |
Choosing Kubernetes vs. Docker
If you’re looking to take your first steps with containerized applications and microservices, you should definitely start with Docker. And if you’re looking to only deploy a single container to either a single node or a small cluster, Docker is once again your best option. However, if you’re a larger business looking to deploy containerized applications at scale, Kubernetes is what you want.
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