Skip to main content

Service Discovery & CoreDNS

Key Takeaways for AI & Readers
  • Naming over IPs: Kubernetes uses Service Names for communication, allowing for stable networking even as individual Pod IPs change.
  • CoreDNS Automation: The cluster's built-in DNS server automatically creates and maintains records for every Service.
  • Service FQDN: The full address of a service follows a standard pattern: service.namespace.svc.cluster.local.
  • Kubelet Integration: The Kubelet automatically configures every container's /etc/resolv.conf to point to CoreDNS.

In Kubernetes, you never hardcode IP addresses. Instead, you use the Service Name. But how does a container know that auth-service actually means 10.96.0.15?

1. Internal DNS Trace​

Visualize how a request is resolved inside the cluster.

📦
Client Pod
📋
CoreDNS
Every Pod's /etc/resolv.conf points to the CoreDNS Service IP. CoreDNS watches the K8s API and automatically maps service names to their ClusterIPs.

2. CoreDNS​

Every cluster has a built-in DNS server called CoreDNS.

  • The Controller: CoreDNS watches the Kubernetes API for new Services.
  • The Records: When a Service is created, CoreDNS automatically creates a DNS record: my-service.my-namespace.svc.cluster.local.

3. How Pods find DNS​

When the Kubelet starts a container, it injects a file: /etc/resolv.conf.

nameserver 10.96.0.10  # This is the CoreDNS ClusterIP
search default.svc.cluster.local svc.cluster.local cluster.local

This tells the OS: "If you can't find a host, ask the Kubernetes DNS server."