New OPS-centric setup. Integrated with wild-init and wild-setup.

setup/cluster/coredns/README.md

@@ -0,0 +1,49 @@
+# CoreDNS
+
+- https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/
+- https://github.com/kubernetes/dns/blob/master/docs/specification.md
+- https://coredns.io/
+
+CoreDNS has the `kubernetes` plugin, so it returns all k8s service endpoints in well-known format.
+
+All services and pods are registered in CoreDNS.
+
+- <service-name>.<namespace>.svc.cluster.local
+- <service-name>.<namespace>
+- <service-name> (if in the same namespace)
+
+- <pod-ipv4-address>.<namespace>.pod.cluster.local
+- <pod-ipv4-address>.<service-name>.<namespace>.svc.cluster.local
+
+Any query for a resource in the `internal.$DOMAIN` domain will be given the IP of the Traefik proxy. We expose the CoreDNS server in the LAN via MetalLB just for this capability.
+
+## Default CoreDNS Configuration
+
+Found at: https://github.com/k3s-io/k3s/blob/master/manifests/coredns.yaml
+
+This is k3s default CoreDNS configuration, for reference:
+
+```txt
+.:53 {
+    errors
+    health
+    ready
+    kubernetes %{CLUSTER_DOMAIN}% in-addr.arpa ip6.arpa {
+      pods insecure
+      fallthrough in-addr.arpa ip6.arpa
+    }
+    hosts /etc/coredns/NodeHosts {
+      ttl 60
+      reload 15s
+      fallthrough
+    }
+    prometheus :9153
+    forward . /etc/resolv.conf
+    cache 30
+    loop
+    reload
+    loadbalance
+    import /etc/coredns/custom/*.override
+}
+import /etc/coredns/custom/*.server
+```