ABAP (ASCS) high availability setup

ABAP (ASCS) high availability setup: The ASCS high availability setup consists of at least two SCS nodes which run the ASCS and ERS instances. Under regular conditions the ERS will always be started on the node where the ASCS is not running. This failover setup has no downtime due to fast failure detection and in-memory data exchange between ES and ERS in case the ASCS must be moved to the failover node. During the failover, the virtual IP address for the ASCS is moved to the failover node too, so its addressing remains unchanged.
Primary and Additional AS node: The Primary AS node and the Additional AS nodes consist of ABAP Application Servers which will be restarted in place in case of software failures. Protection against hardware outages is done by setting up multiple Application Servers on different hardware. Therefore the System Automation for Multiplatforms concept for SAP high availability does not consider failovers of Application Servers to other nodes because Application Server restarts take a lot of time. Other Application Servers must be sized to take the additional workload from failing servers.
Web Dispatcher and SAProuter node (optional): The Web Dispatcher and SAP router high availability setups consists of at least two nodes which run the instances in a failover setup. The components are key for the clients to access the Application Servers, so in case of a failure the instance failover to standby nodes includes their virtual IP addresses too.
Database high availability setup: The database high availability setup is explained in Database high availability installation setup.
NFS high availability setup: The NFS high availability setup is explained in NFS high-availability installation setup.

Setup a ASCS SAP high availability solution with the following components.

Table 1. ABAP resources and the corresponding components
ABAP Resources	SAP component
ABAP resources	ABAP SAP Central Services (ASCS) instances using an own virtual host name on two nodes. Enqueue Replication Server using an own virtual host name on two nodes. Database Server instances using an own virtual host name on two nodes. Primary Application Server for ABAP instance on first node. Additional Application Server for ABAP instances on other nodes.
ABAP independent resources (optional)	Host Agent Web Dispatcher instances using an own virtual host name on two nodes. SAProuter setup on two nodes.