CoreDNS and Service Discovery

Services and Networking / Guide 54 of 103 / Intermediate

• Kubernetes1.36.4
• Cluster4 nodes
• Runtimecontainerd 2.2.6
• CNICalico v3.32.1
• TimeAbout 35 min

The last search domain comes from this lab's DHCP. Yours will differ, and that matters for the ndots count.

• CoreDNSv1.14.2

This guide includes

Use this when a name will not resolve inside the cluster, or when DNS is generating far more queries than anyone expected. This matters because ndots:5 means most short names are tried against every search domain first, and that cost is measurable rather than theoretical.

• reading what the kubelet hands a Pod for DNS, and finding the kube-dns Service in front of CoreDNS
• resolving one Service four different ways and finding which form fails
• setting clusterIP: None and getting every Pod address back instead of one virtual IP
• measuring what ndots:5 actually costs rather than taking the description on trust
• reading the Corefile plugin by plugin

Before you start

• The Services guide, since every name below resolves to a Service.
• A shell Pod with DNS tools. nicolaka/netshoot is used throughout; nslookup and dig are not in normal application images.
• The EndpointSlices guide, for why a headless Service returns the addresses it does.

1. 1

   What a Pod is handed for DNS

2. 2

   One Service, four names, and one that fails

3. 3

   A headless Service hands back the Pods themselves

4. 4

   ndots:5, measured rather than described

5. 5

   The Corefile, plugin by plugin

Official sources

• DNS for Services and Pods
• Customizing DNS Service
• Debugging DNS resolution
• Pod DNS config
• CoreDNS plugins
• NodeLocal DNSCache