List supported protocols for Service (#12669)

Tidy up protocol support to show that TCP and UDP have support in
stable, whereas SCTP support is in alpha. For HTTP, direct users to
read up on Ingress instead.

content/en/docs/concepts/services-networking/service.md

@@ -83,12 +83,9 @@ deploying and evolving your `Services`.  For example, you can change the port
 number that pods expose in the next version of your backend software, without
 breaking clients.
 
-Kubernetes `Services` support `TCP`, `UDP` and `SCTP` for protocols.  The default
+`TCP` is the default protocol for services, and you can also use any other
-is `TCP`.
+[supported protocol](#protocol-support). At the moment, you can only set a
-
+single `port` and `protocol` for a Service.
-{{< note >}}
-SCTP support is an alpha feature since Kubernetes 1.12
-{{< /note >}}
 
 ### Services without selectors
 
@@ -944,29 +941,74 @@ Service is a top-level resource in the Kubernetes REST API. More details about t
 API object can be found at:
 [Service API object](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#service-v1-core).
 
-## SCTP support
+## Supported protocols {#protocol-support}
+
+### TCP
+
+{{< feature-state for_k8s_version="v1.0" state="stable" >}}
+
+You can use TCP for any kind of service, and it's the default network protocol.
+
+### UDP
+
+{{< feature-state for_k8s_version="v1.0" state="stable" >}}
+
+You can use UDP for most services. For type=LoadBalancer services, UDP support
+depends on the cloud provider offering this facility.
+
+### HTTP
+
+{{< feature-state for_k8s_version="v1.1" state="stable" >}}
+
+If your cloud provider supports it, you can use a Service in LoadBalancer mode
+to set up external HTTP / HTTPS reverse proxying, forwarded to the Endpoints
+of the Service.
+
+{{< note >}}
+You can also use {{< glossary_tooltip term_id="ingress" >}} in place of Service
+to expose HTTP / HTTPS services.
+{{< /note >}}
+
+### PROXY protocol
+
+{{< feature-state for_k8s_version="v1.1" state="stable" >}}
+
+If your cloud provider supports it (eg, [AWS](https://kubernetes.io/docs/concepts/cluster-administration/cloud-providers/#aws)),
+you can use a Service in LoadBalancer mode to configure a load balancer outside
+of Kubernetes itself, that will forward connections prefixed with
+[PROXY protocol](https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt).
+
+The load balancer will send an initial series of octets describing the
+incoming connection, similar to this example
+
+```
+PROXY TCP4 192.0.2.202 10.0.42.7 12345 7\r\n
+```
+followed by the data from the client.
+
+### SCTP
 
 {{< feature-state for_k8s_version="v1.12" state="alpha" >}}
 
 Kubernetes supports SCTP as a `protocol` value in `Service`, `Endpoint`, `NetworkPolicy` and `Pod` definitions as an alpha feature. To enable this feature, the cluster administrator needs to enable the `SCTPSupport` feature gate on the apiserver, for example, `“--feature-gates=SCTPSupport=true,...”`. When the feature gate is enabled, users can set the `protocol` field of a `Service`, `Endpoint`, `NetworkPolicy` and `Pod` to `SCTP`. Kubernetes sets up the network accordingly for the SCTP associations, just like it does for TCP connections.
 
-### Warnings
+#### Warnings {#caveat-sctp-overview}
 
-#### The support of multihomed SCTP associations
+##### Support for multihomed SCTP associations {#caveat-sctp-multihomed}
 
 The support of multihomed SCTP associations requires that the CNI plugin can support the assignment of multiple interfaces and IP addresses to a `Pod`.
 
 NAT for multihomed SCTP associations requires special logic in the corresponding kernel modules.
 
-#### Service with type=LoadBalancer
+##### Service with type=LoadBalancer {#caveat-sctp-loadbalancer-service-type}
 
 A `Service` with `type` LoadBalancer and `protocol` SCTP can be created only if the cloud provider's load balancer implementation supports SCTP as a protocol. Otherwise the `Service` creation request is rejected. The current set of cloud load balancer providers (`Azure`, `AWS`, `CloudStack`, `GCE`, `OpenStack`) do not support SCTP.
 
-#### Windows
+##### Windows {#caveat-sctp-windows-os}
 
 SCTP is not supported on Windows based nodes.
 
-#### Userspace kube-proxy
+##### Userspace kube-proxy {#caveat-sctp-kube-proxy-userspace}
 
 The kube-proxy does not support the management of SCTP associations when it is in userspace mode.