Add docs for CloudDualStackNodeIPs docs (KEP-3705) (#40188)

* Document KEP-3705 CloudDualStackNodeIPs

* Clarify --node-ip docs, reference dual-stack docs

Co-authored-by: Tim Bannister <tim@scalefactory.com>

---------

Co-authored-by: Tim Bannister <tim@scalefactory.com>

content/en/docs/concepts/architecture/nodes.md

@@ -93,7 +93,15 @@ For self-registration, the kubelet is started with the following options:
   {{< glossary_tooltip text="taints" term_id="taint" >}} (comma separated `<key>=<value>:<effect>`).
 
   No-op if `register-node` is false.
-- `--node-ip` - IP address of the node.
+- `--node-ip` - Optional comma-separated list of the IP addresses for the node.
+  You can only specify a single address for each address family.
+  For example, in a single-stack IPv4 cluster, you set this value to be the IPv4 address that the
+  kubelet should use for the node.
+  See [configure IPv4/IPv6 dual stack](/docs/concepts/services-networking/dual-stack/#configure-ipv4-ipv6-dual-stack)
+  for details of running a dual-stack cluster.
+
+  If you don't provide this argument, the kubelet uses the node's default IPv4 address, if any;
+  if the node has no IPv4 addresses then the kubelet uses the node's default IPv6 address.
 - `--node-labels` - {{< glossary_tooltip text="Labels" term_id="label" >}} to add when registering the node
   in the cluster (see label restrictions enforced by the
   [NodeRestriction admission plugin](/docs/reference/access-authn-authz/admission-controllers/#noderestriction)).

content/en/docs/concepts/services-networking/dual-stack.md

@@ -79,6 +79,13 @@ An example of an IPv6 CIDR: `fdXY:IJKL:MNOP:15::/64` (this shows the format but
 address - see [RFC 4193](https://tools.ietf.org/html/rfc4193))
 {{< /note >}}
 
+{{< feature-state for_k8s_version="v1.27" state="alpha" >}}
+
+When using an external cloud provider, you can pass a dual-stack `--node-ip` value to
+kubelet if you enable the `CloudDualStackNodeIPs` feature gate in both kubelet and the
+external cloud provider. This is only supported for cloud providers that support dual
+stack clusters.
+
 ## Services
 
 You can create {{< glossary_tooltip text="Services" term_id="service" >}} which can use IPv4, IPv6, or both.

content/en/docs/reference/command-line-tools-reference/feature-gates.md

@@ -83,6 +83,7 @@ For a reference to old feature gates that are removed, please refer to
 | `CSINodeExpandSecret` | `false` | Alpha | 1.25 | 1.26 |
 | `CSINodeExpandSecret` | `true` | Beta | 1.27 | |
 | `CSIVolumeHealth` | `false` | Alpha | 1.21 | |
+| `CloudDualStackNodeIPs` | false | Alpha | 1.27 | |
 | `ComponentSLIs` | `false` | Alpha | 1.26 | |
 | `ContainerCheckpoint` | `false` | Alpha | 1.25 | |
 | `ContextualLogging` | `false` | Alpha | 1.24 | |
@@ -398,6 +399,9 @@ Each feature gate is designed for enabling/disabling a specific feature:
   {{< glossary_tooltip text="PVC" term_id="persistent-volume-claim" >}}.
 - `AppArmor`: Enable use of AppArmor mandatory access control for Pods running on Linux nodes.
   See [AppArmor Tutorial](/docs/tutorials/security/apparmor/) for more details.
+- `CloudDualStackNodeIPs`: Enables dual-stack `kubelet --node-ip` with external cloud providers.
+  See [Configure IPv4/IPv6 dual-stack](/docs/concepts/services-networking/dual-stack/#configure-ipv4-ipv6-dual-stack)
+  for more details.
 - `ContainerCheckpoint`: Enables the kubelet `checkpoint` API.
   See [Kubelet Checkpoint API](/docs/reference/node/kubelet-checkpoint-api/) for more details.
 - `CPUManager`: Enable container level CPU affinity support, see