Chapter 3. HA Solution for S/4HANA based on ABAP Platform 1809 or newer

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 ENSA2, if the ASCS fails, it can start on a separate node in the cluster, and copy the lock entries from the enqueue replicator 2.

In ABAP platform 1809 or newer, the Standalone Enqueue Server 2 (ENSA2) has become the default installation.

Brand new installations 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.

Please refer to Support Policies for RHEL High Availability Clusters - Management of SAP S/4HANA.

With current versions of S/4HANA, it is also possible to run HANA and ABAP Application Server instances on the same system. This makes it possible to have a "cost-optimized" S/4HANA setup where both HANA System Replication and ENSA2 are managed by a single cluster running on the same cluster nodes.

For more information, please refer to Configuring a Cost-Optimized SAP S/4HANA HA cluster (HANA System Replication + ENSA2) using the RHEL HA Add-On.