Kubernetes DNS Concepts: Difference between revisions
(→SkyDNS) |
|||
Line 37: | Line 37: | ||
Note that <code>kube-dns</code> seems to be both the name of the Kubernetes [[#DNS_Service|DNS service]] and the name of a backing provider. | Note that <code>kube-dns</code> seems to be both the name of the Kubernetes [[#DNS_Service|DNS service]] and the name of a backing provider. | ||
==SkyDNS== | ==SkyDNS== | ||
Revision as of 06:14, 20 September 2020
Internal
Overview
Each Kubernetes cluster runs its own DNS service. The DNS service is exposed as a kube-dns Kubernetes ClusterIP service, running in the "kube-system" namespace. The service is backed by two coredns highly-available pods, also deployed in the "kube-system" namespace.
The DNS Service
Each Kubernetes cluster runs an internal DNS service. The DNS service is exposed as a regular Kubernetes ClusterIP service, deployed in the "kube-system" namespace, which in turn exposes the Kubernetes internal DNS server:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns ClusterIP 10.96.0.10 <none> 53/UDP,53/TCP,9153/TCP 49d
The static ClusterIP address allocated to the DNS service (10.96.0.10) is hardcoded into every pod in the cluster, allowing the pods to resolve service names.
Every time a new Kubernetes service is deployed, the Kubernetes cluster automatically updates the internal database with service name to ClusterIP address mappings, making the ClusterIP address of the new service dynamically available to all other pods in the cluster. The mechanism is explained in detail in:
StatefulSets and the individual pods managed by a StatefulSet are also registered with the DNS service.
TODO
- Explain default.svc.cluster.local, svc.cluster.local, cluster.local.
- TODO: https://medium.com/kubernetes-tutorials/kubernetes-dns-for-services-and-pods-664804211501
DNS Operations
DNS Implementation Details
CoreDNS
NAME READY STATUS RESTARTS AGE
coredns-5644d7b6d9-kcxt6 1/1 Running 0 8h
coredns-5644d7b6d9-mztf9 1/1 Running 0 8h
kube-dns
Note that kube-dns
seems to be both the name of the Kubernetes DNS service and the name of a backing provider.