Gateway.spec.listeners

Listeners associated with this Gateway. Listeners define logical endpoints that are bound on this Gateway's addresses. At least one Listener MUST be specified. ## Distinct Listeners Each Listener in a set of Listeners (for example, in a single Gateway) MUST be _distinct_, in that a traffic flow MUST be able to be assigned to exactly one listener. (This section uses "set of Listeners" rather than "Listeners in a single Gateway" because implementations MAY merge configuration from multiple Gateways onto a single data plane, and these rules _also_ apply in that case). Practically, this means that each listener in a set MUST have a unique combination of Port, Protocol, and, if supported by the protocol, Hostname. Some combinations of port, protocol, and TLS settings are considered Core support and MUST be supported by implementations based on the objects they support: HTTPRoute 1. HTTPRoute, Port: 80, Protocol: HTTP 2. HTTPRoute, Port: 443, Protocol: HTTPS, TLS Mode: Terminate, TLS keypair provided TLSRoute 1. TLSRoute, Port: 443, Protocol: TLS, TLS Mode: Passthrough "Distinct" Listeners have the following property: **The implementation can match inbound requests to a single distinct Listener**. When multiple Listeners share values for fields (for example, two Listeners with the same Port value), the implementation can match requests to only one of the Listeners using other Listener fields. When multiple listeners have the same value for the Protocol field, then each of the Listeners with matching Protocol values MUST have different values for other fields. The set of fields that MUST be different for a Listener differs per protocol. The following rules define the rules for what fields MUST be considered for Listeners to be distinct with each protocol currently defined in the Gateway API spec. The set of listeners that all share a protocol value MUST have _different_ values for _at least one_ of these fields to be distinct: * **HTTP, HTTPS, TLS**: Port, Hostname * **TCP, UDP**: Port One **very** important rule to call out involves what happens when an implementation: * Supports TCP protocol Listeners, as well as HTTP, HTTPS, or TLS protocol Listeners, and * sees HTTP, HTTPS, or TLS protocols with the same `port` as one with TCP Protocol. In this case all the Listeners that share a port with the TCP Listener are not distinct and so MUST NOT be accepted. If an implementation does not support TCP Protocol Listeners, then the previous rule does not apply, and the TCP Listeners SHOULD NOT be accepted. Note that the `tls` field is not used for determining if a listener is distinct, because Listeners that _only_ differ on TLS config will still conflict in all cases. ### Listeners that are distinct only by Hostname When the Listeners are distinct based only on Hostname, inbound request hostnames MUST match from the most specific to least specific Hostname values to choose the correct Listener and its associated set of Routes. Exact matches MUST be processed before wildcard matches, and wildcard matches MUST be processed before fallback (empty Hostname value) matches. For example, `"foo.example.com"` takes precedence over `"*.example.com"`, and `"*.example.com"` takes precedence over `""`. Additionally, if there are multiple wildcard entries, more specific wildcard entries must be processed before less specific wildcard entries. For example, `"*.foo.example.com"` takes precedence over `"*.example.com"`. The precise definition here is that the higher the number of dots in the hostname to the right of the wildcard character, the higher the precedence. The wildcard character will match any number of characters _and dots_ to the left, however, so `"*.example.com"` will match both `"foo.bar.example.com"` _and_ `"bar.example.com"`. ## Handling indistinct Listeners If a set of Listeners contains Listeners that are not distinct, then those Listeners are _Conflicted_, and the implementation MUST set the "Conflicted" condition in the Listener Status to "True". The words "indistinct" and "conflicted" are considered equivalent for the purpose of this documentation. Implementations MAY choose to accept a Gateway with some Conflicted Listeners only if they only accept the partial Listener set that contains no Conflicted Listeners. Specifically, an implementation MAY accept a partial Listener set subject to the following rules: * The implementation MUST NOT pick one conflicting Listener as the winner. ALL indistinct Listeners must not be accepted for processing. * At least one distinct Listener MUST be present, or else the Gateway effectively contains _no_ Listeners, and must be rejected from processing as a whole. The implementation MUST set a "ListenersNotValid" condition on the Gateway Status when the Gateway contains Conflicted Listeners whether or not they accept the Gateway. That Condition SHOULD clearly indicate in the Message which Listeners are conflicted, and which are Accepted. Additionally, the Listener status for those listeners SHOULD indicate which Listeners are conflicted and not Accepted. ## General Listener behavior Note that, for all distinct Listeners, requests SHOULD match at most one Listener. For example, if Listeners are defined for "foo.example.com" and "*.example.com", a request to "foo.example.com" SHOULD only be routed using routes attached to the "foo.example.com" Listener (and not the "*.example.com" Listener). If traffic to a Gateway does not match any Listener's hostname (or if the Listener does not specify a hostname and the request does not match any attached Route), the request MUST be rejected. The specific mechanism for rejection depends on the protocol: HTTP returns a 404 status code, while gRPC returns an Unimplemented status code. This concept is known as "Listener Isolation", and it is an Extended feature of Gateway API. Implementations that do not support Listener Isolation MUST clearly document this, and MUST NOT claim support for the `GatewayHTTPListenerIsolation` feature. Implementations that _do_ support Listener Isolation SHOULD claim support for the Extended `GatewayHTTPListenerIsolation` feature and pass the associated conformance tests. ## Compatible Listeners A Gateway's Listeners are considered _compatible_ if: 1. They are distinct. 2. The implementation can serve them in compliance with the Addresses requirement that all Listeners are available on all assigned addresses. Compatible combinations in Extended support are expected to vary across implementations. A combination that is compatible for one implementation may not be compatible for another. For example, an implementation that cannot serve both TCP and UDP listeners on the same address, or cannot mix HTTPS and generic TLS listens on the same port would not consider those cases compatible, even though they are distinct. Implementations MAY merge separate Gateways onto a single set of Addresses if all Listeners across all Gateways are compatible. In a future release the MinItems=1 requirement MAY be dropped. Support: Core