DNS

DNS Records

Services

my-svc.my-namespace.svc.cluster.local
│      │            │   │
│      │            │   └── cluster domain (default: cluster.local)
│      │            └──── service subdomain
│      └──────────────── namespace
└─────────────────────── service name

Pods

Pod (direct pod DNS)

10-244-1-15.default.pod.cluster.local
│           │       │   │
│           │       │   └── cluster domain
│           │       └──── pod subdomain
│           └──────────── namespace
└──────────────────────── pod IP (dashes instead of dots)

StatefulSet Pod (stable identity)

web-0.nginx.default.svc.cluster.local
│     │      │       │   │
│     │      │       │   └── cluster domain
│     │      │       └──── service subdomain
│     │      └──────────── namespace
│     └─────────────────── service name (headless)
└───────────────────────── pod hostname

Pod DNS Policy

• ClusterFirst (default): queries go to CoreDNS first, then upstream
• Default: inherits DNS config from the node
• None: allows custom DNS config via dnsConfig in the pod spec
• ClusterFirstWithHostNet: for pods running with hostNetwork: true

apiVersion: v1
kind: Pod
metadata:
  name: custom-dns-pod
spec:
  containers:
    - name: nginx
      image: nginx
  dnsPolicy: None
  dnsConfig:
    nameservers:
      - 8.8.8.8
      - 8.8.4.4
    searches:
      - my-namespace.svc.cluster.local
      - svc.cluster.local
    options:
      - name: ndots
        value: "5"

CoreDNS

Docs: K8s Docs - Debugging DNS Resolution

Check CoreDNS config file path

kubectl describe deploy -n kube-system coredns | grep Corefile

CoreDNS Corefile key directives

• kubernetes: enables the DNS plugin for the cluster domain
• forward: forwards queries not handled by CoreDNS to upstream DNS (e.g., . /etc/resolv.conf)
• cache: caches DNS responses
• loop: detects and stops forwarding loops
• errors: logs errors

Edit CoreDNS ConfigMap

kubectl edit cm coredns -n kube-system

Troubleshooting DNS

# run a test pod and perform DNS lookup
kubectl run dns-test --image=busybox:1.28 --restart=Never --rm -it -- nslookup <service-name>

# lookup from an existing pod
kubectl exec -it <pod-name> -- nslookup <service-name>.<namespace>.svc.cluster.local

# check CoreDNS pods are running
kubectl get pods -n kube-system -l k8s-app=kube-dns

# check CoreDNS logs
kubectl logs -n kube-system -l k8s-app=kube-dns