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.

It then iterates over each of the status.parents with
a matching Gateway and at least one matching listener.
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 thespec.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:

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

Dualstack Routes¶

Gateway resources may be served from an external-loadbalancer which may support both IPv4 and “dualstack” (both IPv4 and IPv6) interfaces.
External DNS Controller uses the external-dns.alpha.kubernetes.io/dualstack annotation to determine this. If this annotation is
set to true then ExternalDNS will create two records (one A record
and one AAAA record) for each hostname associated with the Route resource.

Example:

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  annotations:
    external-dns.alpha.kubernetes.io/dualstack: "true"
  name: echo
spec:
  hostnames:
    - echoserver.example.org
  rules:
    - backendRefs:
        - group: ""
          kind: Service
          name: echo
          port: 1027
          weight: 1
      matches:
        - path:
            type: PathPrefix
            value: /echo

The above HTTPRoute resource is backed by a dualstack Gateway.
ExternalDNS will create both an A echoserver.example.org record and
an AAAA record of the same name, that each are aliases for the same LB.