Docker vs Kubernetes
People often ask "Docker or Kubernetes?" It is the wrong question. They do different jobs, and in production you usually use both.
Two different jobs
Docker builds and runs containers. One command, one container, on the machine you are typing on.
Kubernetes manages containers at scale. Many containers, many machines, kept running the way you asked.
| Docker | Kubernetes | |
|---|---|---|
| Main job | Build images and run containers | Keep many containers running as you asked |
| Works on | One machine | A group of machines (a cluster) |
| You say | "Run this container now" | "I want 3 of these, always" |
| Container crashes | It stays down unless you set a restart policy on that one host | It is replaced, on any healthy machine |
How they fit together
They are not competitors. A common production setup uses Docker to make the image and Kubernetes to run it:
Who does it?
For each job, pick the tool that is responsible for it.
- Turn a Dockerfile into an image
docker buildmakes the image. Kubernetes never builds images; it only runs them. - Keep 3 copies of posts running at all times
"Always 3" is a desired state. Watching and fixing it is Kubernetes' whole job.
- Run one container on your laptop to test it
docker runis the quick way. A cluster is overkill for one container. - Move work off a machine that just died
Docker only knows its own machine. Kubernetes knows every machine in the cluster and recreates the work elsewhere.
- Scale from 5 copies to 20 when traffic spikes
You change one number, 5 to 20, and Kubernetes starts the rest.
- Push an image to a registry
docker push. Kubernetes later pulls the image from that registry.
Recap
- Docker builds images and runs containers.
- Kubernetes manages containers at scale, across many machines.
- Code → Docker image → container → Kubernetes manages it. You use both.
Docker vs Kubernetes: common questions
Does Kubernetes replace Docker?
No. Docker builds the image and Kubernetes runs and manages the containers made from it. A common setup uses both.