Docker is open-source technology—and a container file format—for automating the deployment of applications as portable, self-sufficient containers that can run in the cloud or on-premises. Docker, Inc., although it shares a similar name, is one of the companies that cultivates the open-source Docker technology to run on Linux and Windows in collaboration with cloud providers like Microsoft.

While the idea of isolating environments is not new and there are other types of containerization software, Docker has grown to be the default container format in recent years. Docker features the Docker Engine, which is a runtime environment. It allows you to build and run containers on any development machine; then store or share container images through a container registry like Docker Hub or Azure Container Registry.

As applications grow to span multiple containers deployed across multiple servers, operating them becomes more complex. While Docker provides an open standard for packaging and distributing containerized apps, the potential complexities can add up fast. How do you coordinate and schedule many containers? How do all the different containers in your app talk to each other? How do you scale many container instances? This is where Kubernetes can help.