Docker vs Kubernetes: What's the Difference?

Your developers keep mentioning Docker and Kubernetes in the same breath, and job posts list both. It is easy to assume they are competing products and you need to pick 1. They are not, and you usually do not.

Docker and Kubernetes work at different levels of the same problem. Docker packages and runs individual containers. Kubernetes coordinates large numbers of containers across many servers. This guide explains the difference in plain English, how they fit together and how to decide whether you need one, both or neither.

The short answer

• Docker is a platform for building, sharing and running containers. It takes your application and everything it needs, packages it into an image, and runs that image as a container on a machine.
• Kubernetes is a system for orchestrating containers. It decides where containers run across a group of servers, keeps the right number running, restarts failed ones, scales them with demand and rolls out updates.

A simple analogy: Docker is the standardized shipping container and the crane that loads it. Kubernetes is the port’s control system, deciding which ship each container goes on, rerouting when a ship breaks down and adding capacity when cargo piles up.

A bit of background on containers

A container packages an application with its libraries, settings and runtime so it behaves the same on a developer’s laptop, a test server and in production. Docker’s documentation describes a container as a lightweight, loosely isolated unit for running an application. Containers share the host machine’s operating system kernel, which makes them faster to start and lighter than full virtual machines.

Docker made containers mainstream after it was released as open source in 2013. Kubernetes followed when Google open-sourced it in 2014, drawing on its experience running containers at huge scale. Kubernetes is now hosted by the Cloud Native Computing Foundation (CNCF).

For a hands-on introduction to containers, see our beginner’s guide to what Docker is.

What Docker does

Docker covers the “build, ship, run” part of the container life cycle:

1. Build: a developer writes a Dockerfile, a text file listing the steps to assemble an image. Running docker build creates the image.
2. Ship: the image is pushed to a registry, such as Docker Hub or a private registry in your cloud account, so others can pull it.
3. Run: docker run starts a container from the image on any machine with a container runtime.

Docker also includes Docker Compose, which defines and runs applications made of several containers (for example, a web app plus a database) from 1 configuration file. It is ideal for local development and simple single-server deployments.

Docker can do basic multi-server orchestration through Docker Swarm mode, but most teams that need serious orchestration choose Kubernetes.

Licensing note: Docker Engine is open source. Docker Desktop, the desktop app most developers use on Mac and Windows, is free for small businesses with fewer than 250 employees and less than $10 million in annual revenue (both conditions must be met), as well as personal use, education and non-commercial open source. Larger organizations and government entities need a paid subscription for professional use.

What Kubernetes does

Kubernetes takes over once you have many containers that need to run reliably across multiple servers. Its documentation lists capabilities including:

• Service discovery and load balancing: routing traffic to healthy containers
• Automated rollouts and rollbacks: updating apps gradually and reverting if something fails
• Self-healing: restarting or replacing containers that crash or fail health checks
• Horizontal scaling: adding or removing copies of an app based on demand
• Secret and configuration management: storing passwords and settings separately from images

You describe the desired state, such as “run 5 copies of this web app,” and Kubernetes continuously works to keep reality matching it. Our full guide to Kubernetes explained goes deeper on how it works and what it costs to run.

Kubernetes does not build images. It runs images that something else, often Docker, has built.

How Docker and Kubernetes work together

In a typical modern workflow, both are present:

1. Developers use Docker on their laptops to build images and test apps locally with Docker Compose.
2. A CI/CD pipeline builds the final image and pushes it to a registry.
3. Kubernetes pulls that image and runs it across a cluster of servers in production.

A common point of confusion: Kubernetes removed its built-in Docker Engine integration, known as “dockershim,” in version 1.24 in 2022. That did not mean Kubernetes stopped supporting Docker images. The Kubernetes project explains that images built with Docker follow the Open Container Initiative (OCI) standard and run on Kubernetes container runtimes such as containerd and CRI-O. Your Dockerfiles and docker build workflow do not need to change.

Key takeaway: Docker and Kubernetes are partners, not rivals. Docker packages your app into a container image. Kubernetes runs and manages many of those containers across many servers. The real decision is whether you need Kubernetes-level orchestration at all.

Side-by-side comparison

When you need Docker, Kubernetes, both or neither

Docker alone (or with Compose) is often enough when: - You have 1 or a few applications - Traffic is modest and predictable - Running on 1 server, with backups, is acceptable - Your team is small and has no dedicated operations staff

You likely need Kubernetes when: - You run many services that must talk to each other reliably - You need high availability across multiple servers or zones - Traffic varies and you want automatic scaling - Several teams deploy independently and need a shared, standardized platform. See our guide to platform engineering.

You may need neither when: - A SaaS product already does the job - Your app fits a managed platform or serverless functions. Our guide to serverless computing explains when that is cheaper and simpler.

There is also a middle ground: managed container services that run your Docker images without you operating Kubernetes, such as AWS Fargate with Amazon ECS, Azure Container Apps or Google Cloud Run. If you do need Kubernetes, managed versions such as Amazon EKS, Azure Kubernetes Service (AKS) and Google Kubernetes Engine (GKE) remove much of the control plane work, though your team still manages workloads, upgrades and costs.

Where to start

1. Containerize first. Write a Dockerfile for your app and run it locally. This is useful even if you never adopt Kubernetes, because the same image runs almost anywhere.
2. Use Docker Compose for local development. Define your app, database and any supporting services in 1 file so every developer has the same setup.
3. Deploy to the simplest platform that works. A managed container service or a single well-maintained server is often enough at the start.
4. Write down your triggers for Kubernetes. For example: more than a handful of services, a need for multi-zone availability, or multiple teams deploying daily. Revisit when you hit them.
5. Build skills deliberately. If Kubernetes is in your future, invest in training. Our guide on how to become a DevOps engineer lists the skills involved.

The bottom line

Docker and Kubernetes are not competitors. Docker packages applications into containers and runs them; Kubernetes orchestrates many containers across many servers. Almost every team working with containers uses Docker or a compatible tool to build images. Far fewer need Kubernetes, which earns its complexity only when you run many services at scale. Start with containers, use the simplest platform that meets your needs and adopt Kubernetes when your scale clearly calls for it.

Sources

• Docker docs: What is Docker? — Docker architecture, images, containers, registries and Compose
• Docker docs: Docker Desktop license agreement — free use thresholds and paid subscription requirements
• Kubernetes: Overview — what Kubernetes does, including self-healing, scaling, rollouts and service discovery
• Kubernetes blog: Dockershim removal FAQ — dockershim removal in v1.24 and compatibility of Docker-built images