add doc for node outbound lb

docs/book/src/SUMMARY.md

@@ -18,6 +18,7 @@
     - [Machine Pools (VMSS)](./topics/machinepools.md)
     - [Managed Clusters (AKS)](./topics/managedcluster.md)
     - [Multitenancy](./topics/multitenancy.md)
+    - [Node Ooutbound Load Balancer](./topics/node-outbound-lb.md)
     - [Spot Virtual Machines](./topics/spot-vms.md)
     - [Virtual Networks](./topics/custom-vnet.md)
     - [Windows](./topics/windows.md)

docs/book/src/topics/node-outbound-lb.md

@@ -0,0 +1,64 @@
+# Node Outbound Load Balancer
+
+This document describes how to configure your clusters' node outbound load balancer.
+
+### Public Clusters
+
+For public clusters ie. clusters with api server load balancer type set to `Public`, CAPZ automatically configures a node outbound load balancer with the default settings.
+
+To provider custom settings for the node outbound load balacer, use the `nodeOutboundLB` section in cluster configuration.
+
+Here is an example of a node outbound load balancer with `frontendIPsCount` set to 3. CAPZ will read this value and create 3 front end ips for this load balancer.
+
+```yaml
+apiVersion: infrastructure.cluster.x-k8s.io/v1alpha4
+kind: AzureCluster
+metadata:
+  name: my-public-cluster
+  namespace: default
+spec:
+  location: eastus
+  networkSpec:
+    apiServerLB:
+      type: Public
+    nodeOutboundLB:
+      frontendIPsCount: 3
+```
+
+<aside class="note warning">
+
+<h1> Warning </h1>
+
+Only `frontendIPsCount` is allowed to be configured for any node outbound load balancer. Trying to modify any other value will result in a validation error.
+
+</aside>
+
+### Private Clusters
+
+For private clusters ie. clusters with api server load balancer type set to `Internal`, CAPZ does not create a node outbound load balancer by default. 
+To create a node outbound load balancer, include the `nodeOutboundLB` section with the desired settings. 
+
+Here is an example of configuring a node outbound load balancer with 1 front end ip for a private cluster:
+
+```yaml
+apiVersion: infrastructure.cluster.x-k8s.io/v1alpha4
+kind: AzureCluster
+metadata:
+  name: my-public-cluster
+  namespace: default
+spec:
+  location: eastus
+  networkSpec:
+    apiServerLB:
+      type: Internal
+    nodeOutboundLB:
+      frontendIPsCount: 1
+```
+
+<aside class="note warning">
+
+<h1> Warning </h1>
+
+Only `frontendIPsCount` is allowed to be configured for any node outbound load balancer. Trying to modify any other value will result in a validation error.
+
+</aside>