mirror of https://github.com/k3s-io/k3s
39 lines
1.7 KiB
Markdown
39 lines
1.7 KiB
Markdown
# DNS Integration with Kubernetes
|
|
|
|
As of kubernetes 0.8, DNS is offered as a cluster add-on. If enabled, a DNS
|
|
Pod and Service will be scheduled on the cluster, and the kubelets will be
|
|
configured to tell individual containers to use the DNS Service's IP.
|
|
|
|
Every Service defined in the cluster (including the DNS server itself) will be
|
|
assigned a DNS name. By default, a client Pod's DNS search list will
|
|
include the Pod's own namespace and the cluster's default domain. This is best
|
|
illustrated by example:
|
|
|
|
Assume a Service named `foo` in the kubernetes namespace `bar`. A Pod running
|
|
in namespace `bar` can look up this service by simply doing a DNS query for
|
|
`foo`. A Pod running in namespace `quux` can look up this service by doing a
|
|
DNS query for `foo.bar`.
|
|
|
|
The cluster DNS server ([SkyDNS](https://github.com/skynetservices/skydns))
|
|
supports forward lookups (A records) and service lookups (SRV records).
|
|
|
|
## How it Works
|
|
|
|
The DNS pod that runs holds 3 containers - skydns, etcd (which skydns uses),
|
|
and a kubernetes-to-skydns bridge called kube2sky. The kube2sky process
|
|
watches the kubernetes master for changes in Services, and then writes the
|
|
information to etcd, which skydns reads. This etcd instance is not linked to
|
|
any other etcd clusters that might exist, including the kubernetes master.
|
|
|
|
## Issues
|
|
|
|
The skydns service is reachable directly from kubernetes nodes (outside
|
|
of any container) and DNS resolution works if the skydns service is targetted
|
|
explicitly. However, nodes are not configured to use the cluster DNS service or
|
|
to search the cluster's DNS domain by default. This may be resolved at a later
|
|
time.
|
|
|
|
## For more information
|
|
|
|
See [the docs for the cluster addon](../cluster/addons/dns/README.md).
|