This article provides information about the main steps describing the application enumeration process and the application launch process in XenApp 6.

Application Enumeration Process

The application enumeration process is as follows:

1. A user launches a Web browser and  then connects to the Web Interface.

2. The Web Interface returns the logon page.

3. The user types in credentials.

4. The user’s credentials are forwarded from XML to the IMA service in HTTP (or HTTPS) form.

5. The IMA then forwards them to the local Lsass.exe.

6. The Lsass.exe encrypts the credentials and passes them to the domain controller.

7. The domain controller returns the SIDs (user’s SID and the list of group SIDs) back to Lsass.exe and to IMA.

8. IMA uses the SIDs to search the Local Host Cache (LHC) for a list of applications and the Worker Group Preference policy for that authenticated user.

9. The list of the applications together with the user’s worker group preference policy are returned to the Web Interface.

10. The Web Interface returns the Web page to the Web browser. (This completes the application enumeration process).
    
    

Application Launch Process

1. User selects the application by clicking the application icon (such as Microsoft Word).

2. The selected application data (Microsoft Word) is passed back to the Web Interface.

3. Web Interface passes the Microsoft Word information together with the user’s Worker Group Preference policy back to IMA on the XML broker server.

4. It then forwards to the IMA service on the Zone Data Collector.

5. The Zone Data Collector tries to find out a least loaded server according to the Worker Group preference list.

6. When it finds the least loaded server, it sends a query to the Citrix Service Manager of that server to verify whether the server has the required application installed. 
    

7. If yes, it provides this server’s host ID to the XML broker.

8. The XML broker translates this host ID into it’s IP address by searching the Local Host Cache.

9. The IP address is then provided to the Web Interface (this completes the application resolution).

10. Web Interface uses this IP address to create the ICA file.

11. The ICA file is then returned to the Web browser on the client machine.

12. Citrix online Web plug-in uses the ICA file to launch an ICA connection to the least loaded XenApp server.
     

13. The XenApp server launches the application for the user.   

A full description of using Worker groups in XenApp 6 along with the new worker group preference and failover policy can be seen in the following whitepaper:
 
CTX124481 – Advanced Farm Administration with XenApp Worker Groups
 
The LBDiag utility is a useful tool to check failover between worker groups per user or group and gives a clear indication of whether the XenApp servers in a worker group have the application that the user is trying to launch installed or not installed.