94 Red Hat OpenShift and IBM Cloud Paks on IBM Power Systems: Volume 1
When configuring multiple masters, the cluster installation process supports the native HA 
method. This method uses the native HA master capabilities that are built into OpenShift 
Container Platform and can be combined with any Load Balancing solution.
If a host is defined in the [lb] section of the inventory file, Ansible installs and configures 
HAProxy automatically as the load balancing solution. If no host is defined, it is assumed that 
you pre-configured an external load balancing solution of your choice to balance the master 
API (port 8443) on all master hosts.
DNS
DNS service is an important component in the Red Hat OpenShift Container Platform 
environment. Regardless of the provider of DNS, an organization is required to have certain 
records in place to serve the various Red Hat OpenShift Container Platform components.
Considering the Load Balancer values for the Red Hat OpenShift Container Platform master 
service and infrastructure nodes running router Pods are known beforehand, entries must be 
configured into the DNS before starting the deployment procedure.
DNS for OpenShift applications
Applications that are served by OpenShift are accessible by the router on ports 80/TCP and 
443/TCP. The router uses a wildcard record to map all host names under a specific sub 
domain to the same IP address without requiring a separate record for each name. This 
process allows Red Hat OpenShift Container Platform to add applications with arbitrary 
names if they are under that sub domain.
For example, a wildcard record for *.apps.example.com causes DNS name lookups for 
app1.apps.example.com and app2.apps.example.com to both return the same IP address: 
9.109.x.y. All traffic is forwarded to the OpenShift Infrastructure Nodes (Routers). The 
Routers examine the HTTP headers of the queries and forward them to the correct 
destination.
With a load-balancer host address of 9.109.x.y, the wildcard DNS record for 
*.apps.example.com resolves IP address 9.109.x.y.
A simple DNS round-robin resolution can be used to spread traffic across infrastructure 
nodes.
For production environments, it is recommended to have more advanced load balancing 
capabilities to distribute the traffic among the OpenShift Routers. In those cases, an external 
Load Balancer is used.
OpenShift Software Defined Networking (SDN)
Red Hat OpenShift Container Platform offers the ability to specify how pods communicate 
with each other. This process can be done by using Red Hat provided Software-defined 
networks (SDN) or a third-party SDN.
Deciding on the suitable internal network for an Red Hat OpenShift Container Platform step is 
a crucial step. Unfortunately, no correct answer exists regarding the suitable pod network to 
chose because this choice varies based on the specific scenario requirements for how a Red 
Hat OpenShift Container Platform environment is to be used.
Note: The HAProxy Load Balancer is intended to demonstrate the API server’s HA mode 
and is not recommended for production environments. If you are deploying to a cloud 
provider, Red Hat recommends deploying a cloud-native TCP-based Load Balancer or 
take other steps to provide a highly available load balancer.