mirror of https://github.com/kubernetes/kops.git
55 lines
1.8 KiB
Markdown
55 lines
1.8 KiB
Markdown
# dns-controller
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dns-controller creates DNS records.
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## Motivation
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In the bring-up of a new cluster, `protokube` has already ensured that
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we have an `etcd` cluster and an `apiserver`. It also sets up DNS
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records for the `etcd` nodes (this is a much simpler problem, because
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we have a 1:1 mapping from an `etcd` node to a DNS name.)
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However, none of the nodes can reach the API server to register. Nor
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can end-users reach the API. In future we might expose the API server
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as a normal service via `Type=LoadBalancer` or via a normal Ingress,
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but for now we just expose it via DNS.
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## How it works
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### Pods with hostNetworking
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dns-controller can add DNS records that point to nodes *with hostNetworking* enabled.
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The dns-controller recognizes annotations on pod.
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* `dns.alpha.kubernetes.io/external` will set up records for accessing
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the resource using the node's public IP.
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* `dns.alpha.kubernetes.io/internal` will set up records for accessing
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the resource using the node's private IP.
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### Services
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#### NodePort
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The controller also recognizes these annotations on `NodePort` services:
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* `dns.alpha.kubernetes.io/external` creates a Route53 A record with
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`public` IPs of all the nodes
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* `dns.alpha.kubernetes.io/internal` creates a Route53 A record with
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`private` IPs of all the nodes
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#### Loadbalancer
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If _either_ of the two annotations are set on a `LoadBalancer` service, it will create a `CNAME` for the load balancer hostname _or_ it will create an A record if the load balancer has an IP.
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### Ingress
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dns-controller can optionally watch `Ingress` resources. To enable this, you need to add the following to the cluster spec:
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```
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spec:
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externalDns:
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watchIngress: true
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```
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dns-controller will then map the specified ingress hostname and the `LoadBalancer` assigned to the ingress.
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