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Each container that you run is repeatable; the standardization from having dependencies included means that you get the same behavior wherever you run it.
Containers decouple applications from underlying host infrastructure. This makes deployment easier in different cloud or OS environments.
A container image is a ready-to-run software package, containing everything needed to run an application: the code and any runtime it requires, application and system libraries, and default values for any essential settings.
Containers are intended to be stateless and immutable: you should not change the code of a container that is already running. If you have a containerized application and want to make changes, the correct process is to build a new image that includes the change, then recreate the container to start from the updated image.
The container runtime is the software that is responsible for running containers.
Usually, you can allow your cluster to pick the default container runtime for a Pod. If you need to use more than one container runtime in your cluster, you can specify the RuntimeClass for a Pod to make sure that Kubernetes runs those containers using a particular container runtime.
You can also use RuntimeClass to run different Pods with the same container runtime but with different settings.