- SAP Managed Tags:
Introduction
Standalone Enqueue Server, a component of Application Server ABAP, is a mechanism to ensure the high availability of the lock table and its entries.
Standalone Enqueue Server has evolved into generation 2 since Netweaver 7.51, known as Standalone Enqueue Server 2, or ENSA2. In ABAP platform 1809, the Standalone Enqueue Server 2 (ENSA2) has become the default installation.
Under the mechanism of the old Standalone Enqueue Server (ENSA1), the ASCS has to fail over to the cluster node where the active ERS is running, because it has to access the shared memory that stores the enqueue replication table. However in ENSA2, if the ASCS failed, it can start on a separate node in the cluster, and copy the lock entries from the enqueue replicator 2.
For this reason, the configuration of ENSA2 in pacemaker is different from ENSA1, in several ways:
- ENSA1 is supported in pacemaker as a two-node cluster configuration, mainly because of the restriction that ASCS must “follow” ERS.
- However because ENSA2 doesn’t have such limitation any more, that makes a multi-node cluster possible
- Customers still have the flexibility of using a two-node cluster for ENSA2
Red Hat’s Support of ENSA2 in Pacemaker
Red Hat has released support for ENSA2 in pacemaker, for applications either from a brand new installation of S/4HANA 1809, or upgraded from older version of Netweaver or S/4HANA.
Brand new installation can take this chance to design the architecture, choosing between multi-node cluster or two-node cluster. Below is the architecture diagram of a typical 3-node cluster. Of course more nodes can be added upon customer’s datacenter requirements or needs:
Upgraded two-node cluster can easily adjust the setup to switch from ENSA1 to ENSA2, without having to make significant changes to the pacemaker infrastructure:
Technical Documentation
The configuration guide for both scenarios can be found in the following documentation:
- SAP Note 2641322 - Installation of ENSA2 and update from ENSA1 to ENSA2 when using the Red Hat HA solutions for SAP
- Red Hat KnowledgeBase Article: Configure SAP S/4HANA ASCS/ERS with Standalone Enqueue Server 2 (ENSA2) in Pacemaker on RHEL 7.6
Availability of the Solution
For deployment on-premise or through Cloud Access, the solution is delivered in Red Hat Enterprise Linux for SAP Solutions. For deployment through RHUI on public cloud, it’s delivered in Red Hat Enterprise Linux for SAP with High Availability and Update Services, a variant of RHEL for SAP Solutions, available through RHUI on public clouds. (Note: at this point the availability varies by cloud provider.)
Questions?
If you have further questions please feel free to leave comments down below.
