Requirements for enabling Regional-DR

This section lists all the prerequisites for implementing the Disaster Recovery solution supported by IBM Fusion Data Foundation.

You must have the following Red Hat OpenShift clusters that have network reachability between them:
- Hub cluster where Red Hat Advanced Cluster Management (RHACM) for Kubernetes operator is installed.
- Primary-managed cluster where Fusion Data Foundation is running.
- Secondary-managed cluster where Fusion Data Foundation is running.
Note: For configuring hub recovery setup, you need a 4th cluster which acts as the passive hub. The primary managed cluster (Site-1) can be co-situated with the active RHACM hub cluster while the passive hub cluster is situated along with the secondary managed cluster (Site-2). Alternatively, the active RHACM hub cluster can be placed in a neutral site (Site-3) that is not impacted by the failures of either of the primary managed cluster at Site-1 or the secondary cluster at Site-2. In this situation, if a passive hub cluster is used it can be placed with the secondary cluster at Site-2. For more information, see Configuring passive hub cluster.
Ensure that RHACM operator and Multicluster Hub is installed on the Hub cluster. For detailed instructions, see the Install guide within Red Hat Advanced Cluster Management for Kubernetes product documentation.
After the operator is successfully installed, a popover with a message that the Web console update is available appears on the user interface. Click Refresh web console from this popover for the console changes to reflect.
Important: Ensure that application traffic routing and redirection are configured appropriately.
On the Hub cluster,
- Navigate to All Clusters > Infrastructure > Clusters.
- Import or create the Primary-managed cluster and the Secondary-managed cluster by using the RHACM console.
- Choose the appropriate options for your environment.
For instructions, see Creating a cluster and Importing a target managed cluster to the hub cluster within the Clusters Red Hat Advanced Cluster Management for Kubernetes product documentation.
Note: Regional-DR is supported with Fusion Data Foundation 4.17 and Red Hat Advanced Cluster Management for Kubernetes 2.11 combinations only.
Connect the private OpenShift cluster and service networks using the RHACM Submariner add-ons. Verify that the two clusters have non-overlapping service and cluster private networks. Otherwise, ensure that the Globalnet is enabled during the Submariner add-ons installation.
Run the following command for each of the managed clusters to determine if Globalnet needs to be enabled. The example shown here is for non-overlapping cluster and service networks so Globalnet would not be enabled.
```
oc get networks.config.openshift.io cluster -o json | jq .spec
```
```
Example output for Primary cluster:

{
  "clusterNetwork": [
    {
      "cidr": "10.5.0.0/16",
      "hostPrefix": 23
    }
  ],
  "externalIP": {
    "policy": {}
  },
  "networkType": "OVNKubernetes",
  "serviceNetwork": [
    "10.15.0.0/16"
  ]
}
```
```
Example output for Secondary cluster:

{
  "clusterNetwork": [
    {
      "cidr": "10.6.0.0/16",
      "hostPrefix": 23
    }
  ],
  "externalIP": {
    "policy": {}
  },
  "networkType": "OVNKubernetes",
  "serviceNetwork": [
    "10.16.0.0/16"
  ]
}
```
Additionally, if Submariner and Fusion Data Foundation are already installed on the managed clusters, use the OpenShift Data Foundation command-line interface (CLI) tool to get additional information about the clusters. This information can determine the need for enabling Globalnet during submariner installation based on the cluster service and private networks. Download the OpenShift Data Foundation CLI tool from the customer portal.

Run the following command on one of the two managed clusters, where PeerManagedClusterName(ClusterID) is the name of the peer Fusion Data Foundation cluster:
```
 odf get dr-prereq <PeerManagedClusterName(ClusterID)>
```
If submariner is not installed with Globalnet on clusters with overlapping services, the following output shows:
```
Info: Submariner is installed.
Info: Globalnet is required.
Info: Globalnet is not enabled.
```
Note: This requires Submariner to be uninstalled and then reinstalled with Globalnet enabled.

If submariner is installed with Globalnet on clusters with overlapping services, the following output shows:
```
Info: Submariner is installed.
Info: Globalnet is required.
Info: Globalnet is enabled.
```
If submariner is installed without Globalnet on clusters with non-overlapping services, the following output shows:
```
Info: Submariner is installed.
Info: Globalnet is not required.
Info: Globalnet is not enabled.
```
If submariner is installed with Globalnet on clusters with non-overlapping services, the following output shows:
```
Info: Submariner is installed.
Info: Globalnet is not required.
Info: Globalnet is enabled.
```
For more information, see Submariner documentation.