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How do I select a runtime component?

As one of the most important components of Kubernetes (K8s), a container runtime manages the lifecycle of images and containers. Kubelet interacts with the container runtime through the Container Runtime Interface (CRI) to manage images and containers.

You can choose Containerd and Docker as container runtime components:

• (Recommended) Containerd has a shorter calling chain and fewer components, and features higher stability and lower node resource consumption.
• Docker should be used as the runtime component in the following situations:
• You need to use docker in docker;
• You need to use commands such as docker build/push/save/load in the TKE node;
• You need to call the docker API;
• You need the docker compose or docker swarm.

How do I modify a runtime component?

1. Log in to the TKE console and click Cluster in the left sidebar.
2. On the Cluster management page, click the target cluster ID to enter the cluster basic information page.
3. Modify the runtime component in the Basic information section.

   Note：

   Modifications on the runtime component and version only take effect for added nodes that are not assigned to any node pool. The existing nodes are not affected.

What are the commands commonly used in Containerd and Docker?

Containerd does not support docker API or docker CLI. However, you can get similar features with the cri-tool command.

What are the differences between the calling chains?

• When Docker is used as the K8s container runtime, the calling chain is as follows:
  kubelet --> docker shim (in the kubelet process) --> dockerd --> containerd
• When Containerd is used as the K8s container runtime, the calling chain is as follows:
  kubelet --> cri plugin (in the containerd process) --> containerd

Although Docker offers more features such as swarm cluster, docker build, and docker API, it may also introduce some bugs and requires one more calling step than containerd.

Stream Service

Note：

Commands such as kubectl exec and kubectl logs require the establishment of a stream forwarding tunnel between the apiserver and the container runtime.

How do I use and configure stream services in Containerd?

The docker API itself provides a stream service, and the docker-shim inside the Kubelet forwards streams through the docker API.
The stream service of Containerd needs to be configured separately:

[plugins.cri]
 stream_server_address = "127.0.0.1"
 stream_server_port = "0"
 enable_tls_streaming = false

What are the configuration differences between versions before and after K8s v1.11?

The stream service of Containerd has different configurations for different versions of K8s.

• Before K8s v1.11:
  Kubelet performs redirection but not stream proxying. That is, Kubelet sends the stream server address opened by containerd to the apiserver which then directly accesses the stream service of containerd. You need to authenticate the stream service forwarder for security purposes.
• After K8s v1.11:
  K8s v1.11 introduced kubelet stream proxy, so that the stream service of containerd only needs to listen to the local address.

Other Differences

Container logs and parameters

CNI network