k3s/cluster/addons/dns/nodelocaldns/README.md

Nodelocal DNS Cache

This addon runs a node-local-dns pod on all cluster nodes. The pod runs CoreDNS as the dns cache. It runs with hostNetwork:True and creates a dedicated dummy interface with a link local ip(169.254.20.10/32 by default) to listen for DNS queries. The cache instances connect to clusterDNS in case of cache misses.

Design details here

nodelocaldns addon template

This directory contains the addon config yaml - nodelocaldns.yaml The variables will be substituted by the configure scripts when the yaml is copied into master. To create a GCE cluster with nodelocaldns enabled, use the command: KUBE_ENABLE_NODELOCAL_DNS=true go run hack/e2e.go -v --up

Network policy and DNS connectivity

When running nodelocaldns addon on clusters using network policy, additional rules might be required to enable dns connectivity. Using a namespace selector for dns egress traffic as shown here might not be enough since the node-local-dns pods run with hostNetwork: True

One way to enable connectivity from node-local-dns pods to clusterDNS ip is to use an ipBlock rule instead:

spec:
  egress:
  - ports:
    - port: 53
      protocol: TCP
    - port: 53
      protocol: UDP
    to:
    - ipBlock:
        cidr: <well-known clusterIP for DNS>/32
  podSelector: {}
  policyTypes:
  - Ingress
  - Egress

Negative caching

The denial cache TTL has been reduced to the minimum of 5 seconds here. In the unlikely event that this impacts performance, setting this TTL to a higher value make help alleviate issues, but be aware that operations that rely on DNS polling for orchestration may fail (for example operators with StatefulSets).