High availability (HA) clustering is a method used to minimize downtime and provide continuous service when certain system components fail. HA clusters consist of multiple nodes that communicate and share information through shared data memory grids and are an effective way to ensure high system availability, reliability, and scalability.

For the Automation Anywhere Control Room application, you can add multiple server nodes under a single Load balancer to support high availability. You can further configure failover clusters to support essential services such as DB service and SVN services.

Enterprise 11: High Availability deployment model

The ability to handle failure allows clusters to meet the following requirements in most data center environments:

• High availability—the ability to provide end users with access to a service for a high percentage of time and reduces unscheduled outages.
• High reliability—the ability to reduce the frequency of system failure.

To support HA for Automation Anywhere, configure the selected components in your data center.

• Cluster components—A cluster is a set of servers (nodes) that are connected using a network and software. In an HA environment, these clusters of servers are required to be in the same physical data center.
  Note: In the context of clusters, though the terms server, host, and node each have specific meaning, they are frequently used interchangeably.
• Cluster group (role)—Group of clustered services that fail over together and are dependent on each other.
• Host—The cluster machine that is hosting the services.
• Node—A generic term for a machine in a cluster.
• Primary node—The active database service or SNV service in a HA cluster where the production activities run.
• Secondary node—The passive/standby duplicate database service or SVN service in a HA cluster that is designated as the target in the event of a failover.
• Graceful degradation—Process allowing cluster dependencies to operate gracefully on a degraded primary node
• Redundancy—HA clusters use redundancy to prevent single points of failure (SPOF), such as a failed server or service. HA clusters include primary (active) servers that host services or databases and secondary (standby) servers that host replicated copies of the services and databases.
• Downtime—Duration of time when a cluster is unable to service request successfully.
• Failover—Failover in HA means the capability to switch essential services such as DB services and SVN services automatically to a standby MS SQL server or SVN server on the failure or abnormal termination of the previously active servers.
• Failback—Failback is the process of restoring the application in a state of failover back to its original state (before failure). The cluster service fails back a group using the same procedures it performs during failover.

Following are the clustered groups (roles) created in HA to support failover:

1. Database HA role group is for a group of database servers configured in a high availability group.

   Database replication—Configure synchronous replication between the primary node (active) and secondary node (standby) MS SQL servers to ensure consistency in the event of a database node failure.In a HA replication system, if the primary database server fails, a secondary database is promoted to primary node.

2. General service group role is for version control of available resources (SVN) to support failover.