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Added k8s_gateway.md (#199)

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Signed-off-by: networkop <mmkashin@gmail.com>
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Michael Kashin
2020-08-20 08:31:28 +02:00
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content/explugins/k8s_gateway.md
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title = "k8s_gateway"
description = "*k8s_gateway* - plugin to resolve all types of external Kubernetes resources."
weight = 10
tags = [ "plugin" , "k8s" ]
categories = [ "plugin", "external", "kubernetes" ]
date = "2020-09-19T12:00:00-08:00"
repo = "https://github.com/ori-edge/k8s_gateway"
home = "https://github.com/ori-edge/k8s_gateway/blob/master/README.md"
+++
## Description
This plugin is very similar to [k8s_external](https://coredns.io/plugins/k8s_external/) but supporting all types of Kubernetes external resources - Ingress, Service of type LoadBalancer and `networking.x-k8s.io/Gateway` (when it becomes available).
This plugin relies on it's own connection to the k8s API server and doesn't share any code with the existing [kubernetes](https://coredns.io/plugins/kubernetes/) plugin. The assumption is that this plugin can now be deployed as a separate instance (alongside the internal kube-dns) and act as a single external DNS interface into your Kubernetes cluster(s).
## Syntax
```
k8s_gateway [ZONE...]
```
Optionally, you can specify what kind of resources to watch and the default TTL to return in response, e.g.
```
k8s_gateway example.com {
resources Ingress
ttl 10
}
```
## Example
``` corefile
. {
k8s_gateway example.com
}
```
With the above configuration the plugin will behave in the following way:
1. All DNS queries will first be matched against the configured zone - `example.com`
2. If there’s a hit, the next step is to match it against any of the existing Ingress resources. The lookup is performed against FQDNs configured in `spec.rules[*].host` fields of the Ingress. At this stage, the result can be returned to the user with IPs collected from the `.status.loadBalancer.ingress`.
3. If no matching Ingress was found, the search continues with the Services objects. Since services don’t really have domain names, the lookup is performed using the `serviceName.namespace` as the key.
4. If there’s a match, it is returned to the end-user in a similar way, alternatively the plugin responds with NXDOMAIN.
## Supported features
`k8s_gateway` resolves Kubernetes resources with their external IP addresses based on zones specified in the configuration. This plugin will resolve the following type of resources:
| Kind | Matching Against | External IPs are from |
| ---- | ---------------- | -------- |
| Ingress | all FQDNs from `spec.rules[*].host` matching configured zones | `.status.loadBalancer.ingress` |
| Service[*] | `name.namespace` + any of the configured zones | `.status.loadBalancer.ingress` |
[*]: Only resolves service of type LoadBalancer
Currently only supports A-type queries, all other queries result in NODATA responses.
> This plugin is **NOT** supposed to be used for intra-cluster DNS resolution and by default will not contain the default upstream [kubernetes](https://coredns.io/plugins/kubernetes/) plugin.