# Gateway sources

The gateway-grcproute, gateway-httproute, gateway-tcproute, gateway-tlsroute, and gateway-udproute
sources create DNS entries based on their respective `gateway.networking.k8s.io` resources.

## Filtering the Routes considered

These sources support the `--label-filter` flag, which filters *Route resources
by a set of labels.

## Domain names

To calculate the Domain names created from a *Route, this source first collects a set
of [domain names from the *Route](#domain-names-from-route).

It then iterates over each of the `status.parents` with
a [matching Gateway](#matching-gateways) and at least one [matching listener](#matching-listeners).
For each matching listener, if the
listener has a `hostname`, it narrows the set of domain names from the *Route to the portion
that overlaps the `hostname`. If a matching listener does not have a `hostname`, it uses
the un-narrowed set of domain names.

### Domain names from Route

The set of domain names from a *Route is sourced from the following places:

* If the *Route is a GRPCRoute, HTTPRoute, or TLSRoute, adds each of the`spec.hostnames`.

* Adds the hostnames from any `external-dns.alpha.kubernetes.io/hostname` annotation on the *Route.
This behavior is suppressed if the `--ignore-hostname-annotation` flag was specified.

* If no endpoints were produced by the previous steps
or the `--combine-fqdn-annotation` flag was specified, then adds hostnames
generated from any`--fqdn-template` flag.

* If no endpoints were produced by the previous steps, each
attached Gateway listener will use its `hostname`, if present.

### Matching Gateways

Matching Gateways are discovered by iterating over the *Route's `status.parents`:

* Ignores parents with a `parentRef.group` other than
`gateway.networking.k8s.io` or a `parentRef.kind` other than `Gateway`.

* If the `--gateway-namespace` flag was specified, ignores parents with a `parentRef.namespace` other
than the specified value.

* If the `--gateway-label-filter` flag was specified, ignores parents whose Gateway does not match the
specified label filter.

* Ignores parents whose Gateway either does not exist or has not accepted the route.

### Matching listeners

Iterates over all listeners for the parent's `parentRef.sectionName`:

* Ignores listeners whose `protocol` field does not match the kind of the *Route per the following table:

| kind       | protocols   |
|------------|-------------|
| GRPCRoute  | HTTP, HTTPS |
| HTTPRoute  | HTTP, HTTPS |
| TCPRoute   | TCP         |
| TLSRoute   | TLS         |
| UDPRoute   | UDP         |

* If the parent's `parentRef.port` port is specified, ignores listeners without a matching `port`.

* Ignores listeners which specify an `allowedRoutes` which does not allow the route.

## Targets

The targets of the DNS entries created from a *Route are sourced from the following places:

1. If a matching parent Gateway has an `external-dns.alpha.kubernetes.io/target` annotation, uses 
the values from that. 

2. Otherwise, iterates over that parent Gateway's `status.addresses`, 
adding each address's `value`. 

The targets from each parent Gateway matching the *Route are then combined and de-duplicated.
