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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).

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).

    Note

    • 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