SAP

In one of the common high-availability cluster design patterns the cluster nodes are distributed across two locations in two different data centers. Many clients expect a similar architecture also for a setup in an IaaS environment. 

The actual network architecture of IBM Power Virtual Server does not allow to span one subnet across multiple workspaces, and communicate from IBM VPC or externally across this subnetwith virtual server instances in both workspaces. So it is not possible to use the well known cluster resource agent IPaddr2 to move the service IP address as cluster resource to a node in a different workspace.

The new resource agent powervs-subnet addresses this limitation for Red Hat HA Add-on clusters. During a takeover event, the resource agent moves the entire subnet, including the IP address, from a virtual server instance in one workspace to a virtual server instance in another workspace.

The following figures illustrate the scenario. SAP HANA is the highly available application in the example. 

Two virtual server instances are deployed in separate workspaces with different subnets.

• SAP HANA is installed on both virtual server instances, and SAP HANA System Replication is configured.
• The two virtual server instances are installed with RHEL, and are configured as a two-node High Availability Add-on cluster with their own subnets.
• A cluster resource that uses resource agent powervs-subnet is configured for Subnet 3 and IP address 3.
• Clients use IP address 3 to connect to the SAP HANA database.

After a cluster takeover

• Subnet 3 is created in workspace 2.
• Subnet 3 is attached to virtual server instance 2.
• IP address 3 is configured on virtual server instance 2.
• The SAP HANA primary is active on virtual server instance 2.

The agent can be downloaded from the ClusterLabs GitHub repository resource-agents. (In future, it will get available as part of a RHEL subscription.)

A comprehensive description for the implementation is part of the IBM Cloud documentation: Implementing a RHEL HA Add-On cluster on IBM Power Virtual Server in a Multizone Region Environment.