Networking

Networking across Nodes is not setup by default by Kubernetes.
There are many other network solutions available:

• cisco
• vmWare
• cilium
• flannel
• calico

From scratch, calico and/or flannel might work.
NSXT might be good in a vmware env.
K8s labs use weavenet as their solution.

The networking solution will assign virtual ips to the nodes && pods.

Services Help

Services help with networking.
A ClusterIP service is used to handle inner-cluster traffic.
A NodePort service is used to allow access into a node from the "outside world". NodePort services first create a clusterIP service, then associate a port on the node to the new clusterIP.
A LoadBalancer helps balance the network traffic across recievers.

Check out This slide deck for another much more verbose look into networking.

CNI Config

K8s is standardizing on the Container Network Interface (CNI) spec for container networking.
This spec

• relates to other librariers that write plugins
• configure container networking
• remove allocated resources when containers are deleted
• aims to provide a common interface between networking oclutions + container runtimes

Something like this

{
  "cniVersion": "0.2.0",
  "name": "this-network",
  "type": "bridge",
  "bridge": "cni0",
  "isGateway": true,
  "ipMasq": true,
  "ipam": {
    "type": "host-local",
    "subnet": "10.22.0.0/16",
    "routes": [{ "dst": "0.0.0.0/0" }]
  }
}

• a linux bridge network
• named cni0
• gives out an IP in a subnet range 10.22.0.0./16

Pod-To-Pod networking

CNI does not help across nodes, unfortunately.
Tools like GKE, Weave, Flannel, Calico, and Cilium help with making all IPs routable without Network Address Translation (NAT).

References

https://research.google/pubs/pub43438/

https://www.gcppodcast.com/post/episode-46-borg-and-k8s-with-john-wilkes/

https://github.com/kubernetes/community