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85 lines
3.6 KiB
Markdown
85 lines
3.6 KiB
Markdown
# Kops dns-controller annotations
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Kops includes a dns-controller, and this document describes the existing annotations and their behaviour. This
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document is intended to allow us to see the use-cases identified by kops dns-controller, to ensure the same annotations
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can be recognized (perhaps with a `--compatibilty` flag), and to ensure that we have comparable functionality.
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## Flags
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* `--dns`: `aws-route53,google-clouddns`
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The DNS flag lets us choose which DNS provider to use.
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* `--watch-ingress` boolean
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Turns ingress functionality on and off. For AWS at least, we are blocked on switching to a release
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from the `kubernetes/ingress` project (instead of one from the `contrib` project).
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* `--zones` configures permitted zones, and also disambiguates when domain names are duplicated. It is a list that matches zones we are allowed to match.
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- `*` and `*/*` are wildcard, and match all zones
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- `example.com` matches zones with name=`example.com`
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- `example.com/1234` matches zones with id=`1234` and name=`example.com`. This is useful to disambiguate between
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multiple zones named `example.com`.
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- `*/1234` matches the zone with id=`1234`. A zone has a unique name, so this is equivalent to `example.com/1234`,
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but a little shorter - and less self-documenting!
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* Standard glog flags (--v, --logtostderr etc)
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* Standard kubectl_util client flags
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## Annotations
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We define 2 primary annotations:
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* `dns.alpha.kubernetes.io/external` which is used to define a DNS record for accessing the resource publicly (i.e. public IPs)
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* `dns.alpha.kubernetes.io/internal` which is used to define a DNS record for accessing the resource from outside the cluster but inside the cloud,
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i.e. it will typically use internal IPs for instances.
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These annotations may both be comma-separated lists of names.
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On a node, we also have a WIP annotation `dns.alpha.kubernetes.io/external-ip`, which configures the external ip
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for a node (to work around [#42125](https://github.com/kubernetes/kubernetes/issues/42125)). That is an annotation
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that lets us defined the equivalent of an address with type ExternalIP.
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## DNS record mappings
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The DNS record mappings try to "do the right thing", but what this means is different for each resource type.
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### Ingress
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We consult the `Status.LoadBalancer.Ingress` records on the ingress. For each one, we create a record.
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If the record is an IP address, we add an A record. If the record is a hostname (AWS ELB), we use a CNAME.
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We would like to use an ALIAS, but we have not yet done this because of limitations of the DNS provider.
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### Pods
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For the external annotation, we will map a HostNetwork=true pod to the external IPs of the node. We create an A record.
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For the internal annotation, we will map a HostNetwork=true pod to the internal IPs of the node. We create an A record.
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We ignore pods that are not HostNetwork=true
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### Services
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* For a Service of Type=LoadBalancer, we look at Status.LoadBalancer.Ingress. We create CNAMEs to hostnames,
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and A records for IP addresses. (We should create ALIASes for ELBs). We do this for both internal & external
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names - there is no difference on GCE or AWS.
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* For a Service of Type=NodePort, we create A records for the node's internal/external IP addresses, as appropriate.
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(A canonical use for NodePort internal is having a prometheus server running inside EC2 monitoring your kubernetes cluster,
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for NodePort external is to expose your service without an ELB).
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### Nodes
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(We don't currently support annotations on the nodes themselves. We do set up internal "alias" records,
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which is how we do JOINs for e.g. NodePort services)
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