Merge pull request #55327 from mtulio/OCPBUGS-6800-aws-lz-fix-mtu

Author: adellape

installing/installing_aws/installing-aws-localzone.adoc

@@ -78,6 +78,12 @@ include::modules/installation-generate-aws-user-infra-install-config.adoc[levelo
 
 include::modules/installation-localzone-generate-k8s-manifest.adoc[leveloffset=+2]
 
+[role="_additional-resources"]
+.Additional resources
+
+* xref:../../networking/changing-cluster-network-mtu.adoc#mtu-value-selection_changing-cluster-network-mtu[Changing the MTU for the cluster network]
+* xref:../../networking/changing-cluster-network-mtu.adoc#nw-ovn-ipsec-enable_configuring-ipsec-ovn[Enabling IPsec encryption]
+
 include::modules/installation-launching-installer.adoc[leveloffset=+1]
 
 include::modules/cli-installing-cli.adoc[leveloffset=+1]

modules/installation-localzone-generate-k8s-manifest.adoc

@@ -26,8 +26,53 @@ $ ./openshift-install create manifests --dir <installation_directory> <1>
 <1> For `<installation_directory>`, specify the installation directory that
 contains the `install-config.yaml` file you created.
 
-. Create the machine set manifests for the worker nodes in your Local Zone.
+. Set the default Maximum Transmission Unit (MTU) according to the network plugin:
++
+[IMPORTANT]
+====
+Generally, the Maximum Transmission Unit (MTU) between an Amazon EC2 instance in a Local Zone and an Amazon EC2 instance in the Region is 1300. See link:https://docs.aws.amazon.com/local-zones/latest/ug/how-local-zones-work.html[How Local Zones work] in the AWS documentation. 
+The cluster network MTU must be always less than the EC2 MTU to account for the overhead. The specific overhead is determined by your network plugin, for example:
+
+- OVN-Kubernetes: `100 bytes`
+- OpenShift SDN: `50 bytes`
+
+The network plugin could provide additional features, like IPsec, that also must be decreased the MTU. Check the documentation for additional information.
+
+====
+
+.. If you are using the `OVN-Kubernetes` network plugin, enter the following command:
++
+[source,terminal]
+----
+$ cat <<EOF > <installation_directory>/manifests/cluster-network-03-config.yml
+apiVersion: operator.openshift.io/v1
+kind: Network
+metadata:
+  name: cluster
+spec:
+  defaultNetwork:
+    ovnKubernetesConfig:
+      mtu: 1200
+EOF
+----
 
+.. If you are using the `OpenShift SDN` network plugin, enter the following command:
++
+[source,terminal]
+----
+$ cat <<EOF > <installation_directory>/manifests/cluster-network-03-config.yml
+apiVersion: operator.openshift.io/v1
+kind: Network
+metadata:
+  name: cluster
+spec:
+  defaultNetwork:
+    openshiftSDNConfig:
+      mtu: 1250
+EOF
+----
+
+. Create the machine set manifests for the worker nodes in your Local Zone.
 .. Export a local variable that contains the name of the Local Zone that you opted your AWS account into by running the following command:
 +
 [source,terminal]