Application Enumeration Process

The application enumeration process is as follows:

1. A user launches a Web browser then connects to 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 then to IMA service in HTTP (or HTTPS) form.

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

6. The Lsass.exe encrypts the credentials then 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 used 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).

The application launch process is as follows:

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

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

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

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

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

16. 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, if the answer is yes, it then provides this server’s host ID to the XML broker.

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

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

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

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

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

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

Function of the Local Host Cache

Each XenApp server stores a subset of the data store in the Local Host Cache (LHC). The LHC performs two primary functions:

• Permits a server to function in the absence of a connection to the data store.

• Improves performance by caching information used by ICA Clients for enumeration and application resolution.

The LHC is an Access database, Imalhc.mdb, stored, by default, in the <ProgramFiles>\Citrix\Independent Management Architecture folder.

The following information is contained in the local host cache:

• All servers in the farm, and their basic information.

• All applications published within the farm and their properties.

• All Windows network domain trust relationships within the farm.

• All information specific to itself. (product code, SNMP settings, licensing information)

On the first startup of the member server, the LHC is populated with a subset of information from the data store. From then on, the IMA service is responsible for keeping the LHC synchronized with the data store. The IMA service performs this task through change notifications and periodic polling of the data store.

If the data store is unreachable, the LHC contains enough information about the farm to allow normal operations for an indefinite period of time, if necessary. However, no new static information can be published, or added to the farm, until the farm data store is reachable and operational again.

Note: Prior to Presentation Server 3.0, the LHC had a grace period of only 96 hours; this was due to farm licensing information being kept on the data store. Once the 96 hour grace period was up, the licensing subsystem would fail to verify licensing, and the server would stop accepting incoming connections.

Because the LHC holds a copy of the published applications and Windows domain trust relationships, ICA Client application enumeration requests can be resolved locally by the LHC. This provides a faster response to the ICA Client for application enumerations because the local server does not have to contact other member servers or the zone data collector. The member server must still contact the zone data collector for load management resolutions.

In some instances it can be necessary to either refresh or recreate the local host cache. The sections below describe these situations.

Refreshing the Local Host Cache

If the IMA service is currently running, but published applications do not appear correctly in ICA Client application browsing, force a manual refresh of the local host cache by executing dsmaintrefreshlhc from a command prompt on the affected server. This action forces the local host cache to read all changes immediately from the data store.

A discrepancy in the local host cache occurs only if the IMA service on a server misses a change event and is not synchronized correctly with the data store.

Recreating the Local Host Cache

If the IMA service does not start, the cause may be a corrupt LHC.

If you have made extensive changes to the farm data store, such as publishing various applications, adding or removing servers from the farm, or creating new policies.

If you must clean the farm data store, using the DSCHECK utility, you should then rebuild the LHC on each of the servers in your farm, once the data store has been cleaned.

Steps to recreate the Local Host Cache

IMPORTANT: The data store server must be available for dsmaintrecreatelhc to work. If the data store is not available, the IMA service cannot start.

1. Stop the IMA service on the XenApp server, if it is started. This can be done using the command: net stop imaservice, or from services.

2. Run dsmaintrecreatelhc, which renames the existing LHC database, creates a new database, and modifies the following registry key HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\IMA\Runtime\PSRequired key to 1. Setting the value PSRequired to 1 forces the server to establish communication with the data store in order to populate the Local Host Cache database. When the IMA service is restarted, the LHC is recreated with the current data from the data store.

3. Restart the IMA service. This can be done via the command line, net start imaservice, or from services.

Note: For XenApp 6 or later the registry key path is HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Citrix\IMA\ RUNTIME\PSRequired to 1.

There is also an available built-in utility to check the Local Host Cache called LHCTestACLsUtil.exe file located in C:\Program Files (x86)\Citrix\System32 of the XenApp server. To run this utility, you must have local administrator privileges.

Consider one of the following resolutions to resolve the errors:

Resolution 1

Complete the following procedure to check that the Web Interface XML configuration is set properly:

1. Open Citrix Web Interface Management.

2. Select XenApp Web Sites.

3. Click Server Farms, as displayed in the following screen shot:

4. Click Edit, as displayed in the following screen shot:

a. Ensure that the correct XML broker(s) are listed under server.

b. Verify that the correct XML port is entered in XML Service Port, as displayed in the following screen shot:

Resolution 2

Complete the following procedure to ensure that both RDP and ICA listeners are not set to a specific network adapter.

1. From the XenApp Server(s) open Administrative Tools.

2. Remote Desktop Services.

3. Remote Desktop Session Host Configuration

4. Select RDP listener.

5. Right click, go into properties and verify all network adapters are selected, as displayed in the following screen shot:

6. After verifying all Network Adapters are selected, review the ICA adapters (only applies to XenApp 6 / Windows 2008 R2 x64). Click on Start > All Programs > Citrix > Administrative Tools > ICA Listener Configuration.

Resolution 3

Complete the following procedure to ensure XenApp 6 policies are configured correctly:

1. Open Citrix Delivery Services Console.

2. Click Policies.

3. Navigate to the Computer tab and Edit the unfiltered policy, as displayed in the following screen shot:

4. When the Identify your policy window opens, click Next.

5. Review your policies and enable the following settings, as displayed in the screen shot:

a. License Server Host

b. License Server Port

c. XenApp Product Edition

d. XML Service Port

6. Save the Policy.

7. Run gpupdate /force from server command prompt, as displayed in the following screen shot:

Resolution 4

Complete the following procedure to ensure that you have registered the correct the port on the XenApp 6 server(s):

1. From the XML broker(s) (XenApp Server) open Services.msc.

2. Ensure the Citrix XML service is started.Note:If the service is not started, you might need to register the correct XML port on the server and restart the service:

Resolution 5

Always clear Local Host Cache on all servers in farm to ensure a fresh copy of the datastore subset is applied to the XenApp and Zone Data Collectors.

Resolution 6

Investigate CDF Tracing using CTX111961 – CDFControl

A customer had a scenario in which all of the servers did not have the application installed. Trace Analysis displayed the following information:

Got the client address from the connection: a.b.c.d

CAppSub::ResolveApplication3(internal) - BrowserName = SGSP4 entered.

QueryZoneMaster[Zone1]: Zone master is [XYZ1].

Entered.InitialProgram = "c:\program files (x86)\netmanage\rumba\AS400\Rumbawsf.Exe" C:\Strategy.wda

SearchPath failed with error 00000002. This could indicate the application is not installed.

CTX_ValidateInitialProgram returned error -3. App may not be installed on the local server.

CAppSub::CrossSubsystemResolveApplication - failed resolve request: 80110200h

CAppSub::ResolveApplication3 (Internal) CrossSubsystemResolveApplication failed: 80110200h

CXMLResponse::ErrorId - Error: mfserver-overloaded

More Information

Though IIS and XML can share the same port by default during an initial installation of XenApp 6, it is recommended as a best practice to assign a different port, for example: 8080 to XML.

Note

The ICA listener configuration described in this article only applies to XenApp 6 / Windows 2008 R2 x64 version.