Q: Clustering appears to reduce performance

We were looking into clustering to increase the availability of the Business Connector (SAP’s branded version of WebMethods).

This is the setup

MachineA: Dedicated Clustering host - which dispatches requests.
MachineB,MachineC,MachineD: WebMethod servers which connect to SAP.

The flow service consisted of a call to SAP (to verify end-to-end connectivity) and a disconnect to free any session resources.

The test was conducted by calling WebMethods with Perl using the LWP::Parallel library. The LWP::Parallel library processes multiple HTTP requests in parallel.

Our findings:

  1. Running the test against a single machine - non clustered - processed 100% of the requests.
  2. Running the same test against the dedicated clustering host - failure rates between 20-50%.

This was totally unexpected as we were hoping for the opposite. The dedicated clustering host decreases performance and availability.

The SAP adapter guide also recommends against using native clustering.

Has anyone else observed a similar situation?
Any ideas about alternative ways to increase availability?