AppSense High Availability

By Gotham
Posted in Virtualization
On February 19, 2012

With VDI becoming more and more popular, many enterprises have turned to AppSense as a solution for managing users’ personal settings, such as Outlook signatures, favorites, and personal dictionaries. The AppSense Personalization Server captures users’ settings and stores them in a SQL database using an agents installed on the users’ workstations. The beauty of AppSense is that it’s focused on the application and is OS-agnostic. Settings captured on a Windows XP machine can be applied to a user’s session running on Windows 7 or Server 2008.

As an integral part of the environment, AppSense calls for high availability and the prevention of a single point of failure. To make AppSense highly available, redundancy should be built around the following essential components: the Management Server, Personalization Server, and SQL Server.

Management Server

The Management Server deploys AppSense agents and configuration packages. If this component fails, no new packages can be deployed. Although this would not normally have a direct impact on the user’s environment, in a DR scenario, it might be necessary to quickly deploy new packages; for example, to map users to different file servers.

AppSense provides the ability to specify a failover Management server either on a global level, which would apply to all agents, or at a deployment group level; however, this solution does not provide load balancing. Using a load balancer, such as a NetScaler or F5, you can distribute the load between management servers. Say an enterprise has four Management servers split between Prod and DR. The enterprise would be able to create one VIP to load balance the Prod servers and one for DR. The DR VIP would only be activated if the Prod VIP fails.

Personalization Server

The Personalization Server captures and stores user settings in a SQL database. The agents provide the Personalization Server with the users’ personal settings, and the Personalization Server uploads that data into a SQL database. Should this component fail, users will have no access to their personal settings. Even if the Personalization Server suffers performance issues, launching applications would slow down dramatically. Therefore, it’s imperative that Personalization Server have no single point of failure and that loads are distributed between servers.

AppSense  provides redundancy for the Personalization Server using sites. Workstations or servers can be made members of a specific site, each site containing both a primary and a secondary Personalization Server. Again, a load balancer should accompany this solution.

SQL Server

The data for the Management and Personalization Servers is kept in a SQL database. Therefore, it’s important that redundancy be built around this component.

SQL Server Cluster

This method comprises two physical servers with shared storage attached. Both servers run the SQL software and are capable of serving up SQL connections. Should one server fail, the other server would pick up where the first server left off without causing any interruptions. In case of failover, no changes are required on the client side, since both servers share a common NetBIOS/DNS name. Though this provides redundancy for a server failure, it won’t provide redundancy if the entire datacenter fails.

SQL Server Log Shipping

In this method, SQL constantly sends the SQL logs to a remote SQL server. Because AppSense does not support SQL mirroring, during a failure, the failover server will have to be manually stood up by a DBA, and the Personalization or Management server will have to be manually re-pointed to the failover SQL server. This is more affordable than clustering, and data can be sent to remote connections and made available in a DR scenario.

Though more expensive, an ideal solution is to combine server clustering and log shipping. This would be the best of both worlds: automatic failover for hardware failure, as well as remote log shipping for a DR scenario.

Gotham Professional Services

Gotham’s Architects and Engineers hold AppSense certificates and are well versed in AppSense technologies. For assistance with AppSense, please contact your Account Manager.

The illustration below depicts what an AppSense environment with redundancy and load balancing might look like.

Highly available AppSense environment