How do you select a container runtime?

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.

TKE supports containerd and Docker as a container runtime:

• (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 if you need to use the following:
  • Docker in docker;
  • Commands such as docker build/push/save/load;
  • Docker API;
  • Docker compose or docker swarm.

What are the commands commonly used in containerd and Docker?

containerd does not support docker API or docker CLI. However, you can get these features with cri-tool commands.

What are the differences between the calling chains of containerd and Docker?

• 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

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

How are stream services used and configured 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 differences between versions before and after k8s 1.11?

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.
• K8s v1.11 and later:
  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 Log and Related Parameters

CNI Network