Local Host Cache (LHC) enables connection brokering operations in a Citrix DaaS (formerly Citrix Virtual Apps and Desktops service) deployment to continue when a Cloud Connector cannot communicate with Citrix Cloud. Local Host Cache engages when the network connection is lost for 60 seconds.

The local host cache can be checked for proper functioning using the information below. This article will explain:

• Troubleshooting Tips and Important Considerations
• LHC Events in the Event Log
• Troubleshooting Tools
• How to verify LHC is working
• Scale and Sizing Considerations for LHC

Instructions

Troubleshooting Tips and important considerations:
-All connectors (to which VDAs register) need to communicate with a StoreFront deployment.  
-Launches across zones (from a broker in one zone to a VDA in a different zone) are not supported during an outage. In multi-resource location environments, if all connectors are listed as part of a single site in StoreFront, this can cause challenges. There are two ways to correct this:

1) If on StoreFront 1912 CU1 or later, enable StoreFront Advanced Health Checking (more info here) via the web.config file. This adds additional granularity to StoreFront’s logic in handling XML responses from connectors.

2) If that’s not an option, each resource location can be specified as a separate site in the StoreFront configuration, you can use Site Aggregation to de-duplicate icons as required.

-Gateway and Connector communications are important during LHC mode.Connectors are also probably serving as your STA in a Citrix Cloud world. To make sure connectors are properly detected as available or not available to handle STA functions in LHC mode, the Citrix ADC has a built-in monitor to detect availability of the broker service on Cloud Connectors including use as a STA for Gateway connections. Learn more here. Other monitors (tcp, ping) may not correctly identify that the STA is unavailable on non-elected Connectors during LHC mode.

Checking the Event Logs for LHC events:
During normal operations, the following events can occur when the CSS imports the configuration data into the Local Host Cache database using the Local Host Cache broker.

Config Sync Service

• 503: The Citrix Config Sync Service received an updated configuration. This event occurs each time an updated configuration is received from Citrix Cloud. It indicates the start of the synchronization process.
• 504: The Citrix Config Sync Service imported an updated configuration. The configuration import completed successfully.
• 505: The Citrix Config Sync Service failed an import. The configuration import did not complete successfully. If a previous successful configuration is available, it is used if an outage occurs. However, it will be out-of-date from the current configuration. If there is no previous configuration available, the service cannot participate in session brokering during an outage. In this case, see the Troubleshoot section, and contact Citrix Support.
• 507: The Citrix Config Sync Service abandoned an import because the system is in outage mode and the Local Host Cache broker is being used for brokering. The service received a new configuration, but the import was abandoned because an outage occurred. This is expected behavior.
• 510: No Configuration Service configuration data received from primary Configuration Service.
• 517: There was a problem communicating with the primary Broker.
• 518: Config Sync script aborted because the secondary Broker (High Availability Service) is not running.

High Availability Service

This service is also known as the Local Host Cache broker.

• 3502: An outage occurred and the Local Host Cache broker is performing broker operations.
• 3503: An outage was resolved and normal operations have resumed.
• 3504: Indicates which Local Host Cache broker is elected, plus other Local Host Cache brokers involved in the election.

Troubleshooting Tools:
Several troubleshooting tools are available when a synchronization import to the Local Host Cache database fails and a 505 event is posted.  Please refer to our docs for more information

How to Verify Local Host Cache is Working
Scaling and Size considerations for Local Host Cache