Container Engine

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).

CCE supports containerd and Docker. containerd is recommended for its shorter traces, fewer components, higher stability, and less consumption of node resources.

Table 1 Comparison between container engines

Item	containerd	Docker
Tracing	kubelet --> CRI plugin (in the containerd process) --> containerd	Docker (Kubernetes v1.23 and earlier): kubelet --> dockershim (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
Command	crictl	docker
Kubernetes CRI	Native support	Support through dockershim or cri-dockerd
Pod delayed startup	Minor	High
kubelet CPU/memory usage	Minor	High
Runtime's CPU/memory usage	Minor	High

Mapping between Node OSs and Container Engines

Table 2 Node OSs and container engines in CCE clusters

OS	Kernel Version	Container Engine	Container Storage Rootfs	Container Runtime
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 Clusters of v1.23 and later support containerd.	OverlayFS	runC
HCE OS 2.0	5.x	Docker containerd	OverlayFS	runC

Table 3 Node OSs and container engines in CCE Turbo clusters

Node Type	OS	Kernel Version	Container Engine	Container Storage Rootfs	Container Runtime
ECS (VM)	EulerOS 2.9	4.x	Docker containerd	OverlayFS	runC
	HCE OS 2.0	5.x

Common Commands of containerd and Docker

containerd does not support Docker APIs and Docker CLI, but you can run crictl commands to implement similar functions.

Table 4 Image-related commands

No.	Docker Command	containerd Command	Remarks
1	docker images [Option] [Image name[:Tag]]	crictl images [Option] [Image name[:Tag]]	List local images.
2	docker pull [Option] Image name[:Tag|@DIGEST]	crictl pull [Option] Image name[:Tag|@DIGEST]	Pull images.
3	docker push	None	Pushing images.
4	docker rmi [Option] Image...	crictl rmi [Option] Image ID...	Delete a local image.
5	docker inspect Image ID	crictl inspecti Image ID	Check images.

Table 5 Container-related commands

No.	Docker Command	containerd Command	Remarks
1	docker ps [Option]	crictl ps [Option]	List containers.
2	docker create [Option]	crictl create [Option]	Create a container.
3	docker start [Option] Container ID...	crictl start [Option] Container ID...	Start a container.
4	docker stop [Option] Container ID...	crictl stop [Option] Container ID...	Stop a container.
5	docker rm [Option] Container ID...	crictl rm [Option] Container ID...	Delete a container.
6	docker attach [Option] Container ID	crictl attach [Option] Container ID	Connect to a container.
7	docker exec [Option] Container ID Startup command [Parameter...]	crictl exec [Option] Container ID Startup command [Parameter...]	Access the container.
8	docker inspect [Option] Container name|ID...	crictl inspect [Option] Container ID...	Query container details.
9	docker logs [Option] Container ID	crictl logs [Option] Container ID	View container logs.
10	docker stats [Option] Container ID...	crictl stats [Option] Container ID	Check the resource usage of the container.
11	docker update [Option] Container ID...	crictl update [Option] Container ID...	Update container resource limits.

Table 6 Pod-related commands

No.	Docker Command	containerd Command	Remarks
1	None	crictl pods [Option]	List pods.
2	None	crictl inspectp [Option] Pod ID...	View pod details.
3	None	crictl start [Option] Pod ID...	Start a pod.
4	None	crictl runp [Option] Pod ID...	Run a pod.
5	None	crictl stopp [Option] Pod ID...	Stop a pod.
6	None	crictl rmp [Option] Pod ID...	Delete a pod.

Note

Containers created and started by containerd are immediately deleted by kubelet. containerd does not support suspending, resuming, restarting, renaming, and waiting for containers, nor Docker image build, import, export, comparison, push, search, and labeling. containerd does not support file copy. You can log in to the image repository by modifying the configuration file of containerd.

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-engine 18.9.0, a Docker version customized for CCE. Security vulnerabilities will be fixed in a timely manner.

• containerd: 1.6.14

last updated: 2024-05-09 02:02