If you use Services of type Headless, CoreDNS will have to subscribe to changes to the endpoints and reconfigure itself every time an endpoint is added or removed. There are more examples of Kubernetes components that subscribe to changes to endpoints.ĬoreDNS, the DNS component in the cluster, is another example. You can imagine that inspecting etcd would reveal not just where the Pod is running, but also its IP address. It's the job of the kubelet to collect all the details of the Pod such as the IP address and report them back to the control plane. No one told the master node that the Pod has an IP address assigned and it's ready to receive traffic.Īs far the control plane is concerned, the Pod is still being created. The kubelet knows about the IP address (because it invoked the Container Network Interface), but the control plane does not. When the Container Network Interface finishes its job, the Pod is connected to the rest of the network and has a valid IP address assigned.
Connecting the container to the rest of the network.Īs you can imagine, there are several ways to connect the container to the network and assign a valid IP address (you could choose between IPv4 or IPv6 or maybe assign multiple IP addresses).Īs an example, Docker creates virtual ethernet pairs and attaches it to a bridge, whereas the AWS-CNI connects the Pods directly to the rest of the Virtual Private Cloud (VPC).Generating a valid IP address for the Pod.The Container Networking Interface (CNI) is a bit more interesting because it is in charge of:
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