Merge pull request #28358 from dulek/kuryr-service-subnet-note

Bug 1910665: Kuryr: Add note about expected OpenStack subnet

Author: maxwelldb

modules/installation-osp-kuryr-config-yaml.adoc

@@ -40,25 +40,25 @@ networking:
   machineNetwork:
   - cidr: 10.0.0.0/16
   serviceNetwork:
-  - 172.30.0.0/16
+  - 172.30.0.0/16 <1>
   networkType: Kuryr
 platform:
   openstack:
     cloud: mycloud
     externalNetwork: external
     computeFlavor: m1.xlarge
     lbFloatingIP: 128.0.0.1
-    trunkSupport: true
-    octaviaSupport: true
+    trunkSupport: true <2>
+    octaviaSupport: true <2>
 pullSecret: '{"auths": ...}'
 sshKey: ssh-ed25519 AAAA...
 ----
-
-[NOTE]
-====
-Both `trunkSupport` and `octaviaSupport` are automatically discovered by the
+<1> The Amphora Octavia driver creates two ports per load balancer. As a
+result, the service subnet that the installer creates is twice the size of the
+CIDR that is specified as the value of the `serviceNetwork` property. The larger range is
+required to prevent IP address conflicts.
+<2> Both `trunkSupport` and `octaviaSupport` are automatically discovered by the
 installer, so there is no need to set them. But if your environment does not
 meet both requirements, Kuryr SDN will not properly work. Trunks are needed
 to connect the pods to the {rh-openstack} network and Octavia is required to create the
 {product-title} services.
-====