external-dns/docs/sources/gateway.md

Gateway sources

The gateway-grpcroute, 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-name flag was specified, ignores parents with a parentRef.name other than the specified value.

  For example, given the following HTTPRoute:

  apiVersion: gateway.networking.k8s.io/v1
  kind: HTTPRoute
  metadata:
    name: echo
  spec:
    hostnames:
      - echoserver.example.org
    parentRefs:
      - group: networking.k8s.io
        kind: Gateway
        name: internal
  ---
  apiVersion: gateway.networking.k8s.io/v1
  kind: HTTPRoute
  metadata:
    name: echo2
  spec:
    hostnames:
      - echoserver2.example.org
    parentRefs:
      - group: networking.k8s.io
        kind: Gateway
        name: external
  

  And using the --gateway-name=external flag, only the echo2 HTTPRoute will be considered for DNS entries.

• 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 the route has the external-dns.alpha.kubernetes.io/target annotation with a non-empty value, uses the value from that.

2. If the route has the external-dns.alpha.kubernetes.io/target: "" it will disable the external-dns.alpha.kubernetes.io/target on the matching parent Gateway(s) and continue the regular flow from step 4.

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

4. 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. When using the AWS Route53 provider, External DNS Controller will always create both A and AAAA alias DNS records by default, regardless of whether the load balancer is dual stack or not.

Example

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