WHY KUBERNETES DEPRECATE DOCKER ?
By now, we likely heard the news — Kubernetes is deprecating Docker After it’s v1.20 release. What’s really happened ?
Essentially, “Docker” is made up of several pieces, including user interface among other things. As a result Docker come human friendly Abstraction layer , what’s actually happening is that dockershim is being removed from Kubelet. In other words, Docker will not be used as the default container runtime. However, you may still integrate Docker into your environment.
Dockershim was a temporary solution proposed by the Kubernetes community to add support for Docker so that it could serve as its container runtime. Dockershim deprecation only means the code maintenance of Dockershim in the code repository of Kubernetes will stop. This is because Dockershim has become a heavy burden on the Kubernetes maintainers. After this change, the Kubernetes community will be able to maintain the Kubernetes Container Runtime Interface (CRI) only. In fact, all CRI-compliant runtimes can be the runtime for Kubernetes, such as CRI-O and containerd.
Currently, the KubeSphere container platform is using Docker as the container runtime of Kubernetes. Meanwhile, it also supports any CRI-compliant implementations. For KubeSphere and Docker users, dockershim deprecation does not affect the existing KubeSphere system and will not take any toll on your cluster or on your business. KubeSphere users can continue to use Docker which has already been tested at scale.
In future releases, other KubeSphere components, such as DevOps, will support these container runtimes and you will be able to use these CRI implementations.
CRI-O
CRI-O, an open-source project started by Red Hat, is an implementation of the Kubernetes CRI to enable using OCI (Open Container Initiative) compatible runtimes. It allows Kubernetes to use any OCI-compliant runtime as the container runtime for running Pods.
containerd
containerd, a Cloud Native Computing Foundation graduated project, is an industry-standard container runtime with an emphasis on simplicity, robustness and portability. It manages the complete container lifecycle of its host system.
containerd is available as a daemon for Linux and Windows. It manages the complete container lifecycle of its host system, from image transfer and storage to container execution and supervision to low-level storage to network attachments and beyond.
Architecture
About the Open Container Initiative(OCI)
The Open Container Initiative is an open governance structure for the express purpose of creating open industry standards around container formats and runtime. Projects associated with the Open Container Initiative can be found at https://github.com/opencontainers and we recommend you get involved with the community at https://www.opencontainers.org/community.
To support this UX the OCI Image Format contains sufficient information to launch the application on the target platform (e.g. command, arguments, environment variables, etc). This specification defines how to create an OCI Image, which will generally be done by a build system, and output an image manifest, a filesystem (layer) serialization, and an image configuration. At a high level the image manifest contains metadata about the contents and dependencies of the image including the content-addressable identity of one or more filesystem serialization archives that will be unpacked to make up the final runnable filesystem. The image configuration includes information such as application arguments, environments, etc. The combination of the image manifest, image configuration, and one or more filesystem serializations is called the OCI Image.
Docker is donating its container format and runtime, runC, to the OCI to serve as the cornerstone of this new effort. It is available now at https://github.com/opencontainers/runc.
runC
runC, a lightweight universal container runtime, is a command-line tool for spawning and running containers according to the Open Container Initiative (OCI) specification. That’s the short version. The long version: The governance umbrella created by Docker, Google, IBM, Microsoft, Red Hat, and many other partners to create a common and standardized runtime specification has a readable spec document for the runtime elements of a container, and a usable implementation based on code contributed to the OCI by Docker. It includes libcontainer, the original lower-layer library interface originally used in the Docker engine, to set up the operating system constructs that we call a container.