Introduction to Container Engines

Container engines, one of the most important components of Kubernetes, manage the lifecycle of images and containers. The kubelet interacts with a container runtime through the Container Runtime Interface (CRI).

Mapping between Node OSs and Container Engines

**Table 1** Node OSs and container engines in CCE clusters
OS	Kernel Version	Container Engine	Container Storage Rootfs	Container Runtime
CentOS 7.x	3.x	Docker Clusters of v1.23 and later support containerd.	Clusters of v1.19.16 and earlier use Device Mapper. Clusters of v1.19.16 and later use OverlayFS.	runC
EulerOS 2.5	3.x	Docker	Device Mapper	runC
EulerOS 2.9	4.x	Docker Clusters of v1.23 and later support containerd.	OverlayFS	runC
Ubuntu 22.04	4.x	Docker containerd	OverlayFS	runC

**Table 2** Node OSs and container engines in CCE Turbo clusters
Node Type	OS	Kernel Version	Container Engine	Container Storage Rootfs	Container Runtime
Elastic Cloud Server (VM)	CentOS 7.x	3.x	Docker	OverlayFS	runC
	EulerOS 2.5	3.x	Docker	OverlayFS	runC
	EulerOS 2.9	4.x	Docker Clusters of v1.23 and later support containerd.	OverlayFS	runC
	Ubuntu 22.04	4.x	Docker containerd	OverlayFS	runC

Differences in Tracing

Docker (Kubernetes 1.23 and earlier versions):
kubelet --> docker shim (in the kubelet process) --> docker --> containerd
Docker (community solution for Kubernetes v1.24 or later):
kubelet --> cri-dockerd (kubelet uses CRI to connect to cri-dockerd) --> docker--> containerd
containerd:
kubelet --> cri plugin (in the containerd process) --> containerd

Although Docker has added functions such as swarm cluster, docker build, and Docker APIs, it also introduces bugs. Compared with containerd, Docker has one more layer of calling. Therefore, containerd is more resource-saving and secure.

Container Engine Version Description

Docker
- EulerOS/CentOS: docker 18.9.0, a Docker version customized for CCE. Security vulnerabilities will be fixed in a timely manner.
- Ubuntu 22.04: docker-ce 20.10.21 (community version).
- You are advised to use the containerd engine for Ubuntu nodes.
- The open source docker-ce of the Ubuntu 18.04 node may trigger bugs when concurrent exec operations are performed (for example, multiple exec probes are configured). You are advised to use HTTP/TCP probes.
containerd: 1.6.14