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external-dns/docs/sources/gateway.md
John Gardiner Myers 6b230c6c44 Document the Gateway sources
2023-09-16 14:18:16 -07:00

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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:

  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.