# DNS not working inside a Kubernetes pod (could not resolve host / nslookup: can't resolve)

**Code:** `DNS in pod` · **Category:** Kubernetes · **Seen on:** Kubernetes

Pods can’t resolve service names or external hosts — CoreDNS is down, blocked by NetworkPolicy, or the upstream resolver fails.

## Meaning

Pods use CoreDNS (kube-dns service). Problems: CoreDNS pods crashing or overloaded, NetworkPolicies blocking UDP/TCP 53, wrong ndots search behaviour causing slow lookups, or the node’s upstream DNS failing.

## Common causes

- CoreDNS pods not running/crashlooping (often a loop with host resolv.conf)
- NetworkPolicy blocks egress to kube-dns port 53
- Upstream DNS unreachable from nodes
- Using short names across namespaces (svc instead of svc.namespace)

## Quick fix

1. Test from a debug pod: nslookup kubernetes.default
2. Check CoreDNS pods and logs
3. Allow DNS egress in NetworkPolicies

## Detailed fix by platform

### Kubernetes

1. 

```bash
kubectl run dns-test --rm -it --image=busybox:1.36 --restart=Never -- nslookup kubernetes.default
kubectl -n kube-system logs -l k8s-app=kube-dns --tail=50
```


## How to diagnose

1. **CoreDNS** — Pods Running? Logs?
2. **Policy** — Egress to port 53 allowed?
3. **Name** — Using svc.namespace.svc.cluster.local?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/kubernetes/pod-dns-resolution-failure)