@kodekloud: K8s Debugging: Fixing Unreachable Cluster DNS! When a Kubernetes pod loses the ability to resolve names, your first line of defense is checking the health of the CoreDNS pods inside the kube-system namespace. If these pods are crashing or stuck in a restart loop, the culprit is almost always a broken Corefile configuration. The Corefile orchestrates your entire cluster's DNS routing through critical plugins: kubernetes for mapping internal service names, forward for routing public traffic to upstream resolvers, cache for memory efficiency, and loop to detect and kill infinite routing loops. Even a minor syntax error or typo in this file will trigger a catastrophic, cluster-wide DNS blackout. If CoreDNS is perfectly healthy but your application pods still can't reach it, a restrictive Network Policy is likely blocking the traffic. Applying a global ""default deny egress"" policy instantly cuts off a pod's outbound communications, including its critical path to the cluster DNS. To fix this, you must explicitly inject an egress rule allowing outbound traffic on port 53 for both UDP and TCP protocols. Because Kubernetes network policies cannot target a cluster Service object directly, you must configure your rule to allow traffic either directly to the CoreDNS pods via their selector labels or to the specific cluster DNS IP address using an IP block. Save this for your next K8s outage. Or your next interview. ▶️ Part 1: https://youtube.com/shorts/J-zSd2lsMaI ▶️ Part 3: https://youtube.com/shorts/Tieokbq9jWg #Kubernetes #K8s #CoreDNS #NetworkPolicy #DevOps #SRE #Troubleshooting #SysAdmin #CloudNative #PlatformEngineering #Networking #TechTips #Backend

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Friday 29 May 2026 16:06:16 GMT