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It is not necessary to install the AppSync Host Plug-in on all the nodes that are part of the availability group. The plug-in must be only installed on the node that hosts the databases that AppSync protects.
If an instance is clustered, the plug-in must be installed on all the nodes for which the instance can failover. The virtual server must be added to AppSync as described in the Protecting databases in clustered instances section. If an instance is not clustered, ensure that the node on which the instance is installed is registered to AppSync.
The following figure is an example of how to protect databases in a three-node cluster with one clustered instance of SQL Server and one non-clustered instance. Lrmj183 and Lrmj182 are the possible owners of the clustered instance. Lrmj185 is the virtual server network name of the clustered instance. Lrmj181 hosts a non-clustered instance of SQL Server. Protecting databases on any node in the cluster, the cluster nodes Lrmj183 and Lrmj182 are added to AppSync and the host plug-ins are installed. Then Lrmj185, the virtual server, is added.
The following figure shows the clustered instance LRMJ185 and the non-clustered instance LRMJ183\AG_STANDALONE.
Enabling Auto Switch to Copy, ensures that AppSync automatically switches to the Copy backup type when the service plan is configured to do a Full backup and the database is a secondary replica.
Figure 6 and Figure 7 show the information that AppSync gathers for databases in availability groups and if the database role is primary or secondary. If the role is secondary, the type of commit that is configured is also shown. The Database Status column shows if the database is online, and if AppSync can protect it. When Online, readable is displayed, AppSync protects the secondary database. When Online, not readable is displayed, and the secondary database’s Readable Secondary option is not set to Yes within SQL Management Studio, the secondary database is not protected by AppSync. Read-intent only is not supported with AppSync 4.3 and lower. See Figure 8 for an example of the Readable Secondary options. AppSync 4.4 and greater will protect secondary databases if Readable, Secondary is set to Yes or Read-intent only. The secondary databases will show Online, read-intent only as the database status, for databases which have the Readable Secondary option set to Read-intent only. In case of failover, the primary database would be skipped from the service plan protection, and its status will be shown as offline in the AppSync user interface.