The container-oriented approach has the following key concepts:

• Container Host: The Container Host is like an engine for containers and it can run multiple containers. And it can configure the virtual machine to host containers.
• Container: It is a runtime instance of an image.
• Container image: An application needs several resources to run, such as layered filesystems, OS, and configurations. The container image consists of everything an application requires. The container image is immutable in nature. It cannot change its state as it's deployed to different environments.
• Container OS image: The container OS image is created from several other container images to make up a container. It also can't be modified.
• Container repository: It is used to store the container image and its related dependencies. It can be local repository used each time a container image is created. You can reuse these images many times on the container host. Docker Hub is an example of a container repository. They can be used across different container hosts.

As you can see, the preceding list outlined key concepts and approaches for using a container-based infrastructure for your microservices-based application. This is a very popular approach and adopted by several companies in distributed application development and deployment. Docker is an example and implementation of this approach. Let's discuss Docker as a container in the next section.