1.    Introduction
High Availability of an application or service provided to the end 
user and reducing the downtime of the outages occurred if any (Disaster 
Recovery Management) plays a major role in the lifecycle of any 
application. System outages are either anticipated
 (planned) or result of failures (unplanned) which may lead to data loss
 directly/indirectly impacts the end user requirements. In these 
situations, the primary objective of the software engineers/developers 
is to bring back the system online as soon as possible
 with minimal the data loss. AlwaysOn is a feature in 
the SQL server 2012 which provides flexible and cost efficient high 
availability and disaster recovery solution. AlwaysOn provides automatic
 recovery from failures avoiding the downtime
 which increases the high availability of critical applications online 
thereby reducing the data loss. AlwaysOn can be configured at both 
database level and instance level.
1.1.       Availability Groups (AG) & AG Listener
Availability group is a collection of databases in which AlwaysOn is 
configured at database level. Availability group enhances capabilities 
of database mirroring and ensures the availability of databases. Client 
application connects to the Availability group’s
 databases through a virtual network name called Availability group 
listener (AG Listener).Client need not required to find the active 
physical instance of the SQL server instead Client connects to the AG 
Listener which determines the available primary SQL
 server. A SQL server instance can have multiple availability groups.
1.2.       Availability Replicas and Roles
Availability Replicas are the user databases residing in the 
Availability Group (AG). Each database in the availability group can 
have a maximum of four availability replicas but only one replica in the
 AG can act as primary replica which is enabled for
 read-write operations and remaining replicas act as secondary read only
 replicas. The secondary replicas are considered as the backup.
        
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