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Session reliability on NetScaler high availability pair

June 17, 2019
Contributed by:  C

When a network disruption or a device failover occurs during an ICA session, session reconnection can use one of two mechanisms: Session Reliability or Auto Client Reconnect.

Session Reliability, the preferred mode, is a seamless experience for the user. The disruption is barely noticeable for brief network interruptions.

Auto Client Reconnect, the fallback option, involves restarting the client. This mechanism is disruptive for the user and is not always supported.

Receivers can now reconnect their ICA sessions seamlessly using the ICA Session Reliability feature, when HDX Insight is enabled. This feature works both in standalone and in a NetScaler HA pair configuration and even when a NetScaler failover happens.

Note

  • NetScaler appliances should be running on software version 11.1 build 49.16 or later.
  • You should not enable or disable Session Reliability mode when the NetScaler appliances have active connections.
  • Enabling or disabling the feature when connections are still active causes HDX Insight to stop parsing those sessions after a failover occurs and result in loss of information about the sessions.
  • Session Reliability on a high availabilty setup is disabled by default for NetScaler software version 11.1 49.16 or later. Session reliability is supported on a high availability setup only if both the nodes of the setup run the same build (for example, release 11.1 build 53). In other words, session reliability is not supported on a high availability setup if both the nodes run different builds (for example, one node has release 11.1 build 53 whereas the other has release 11.1 build 56).

To configure Session reliability from NetScaler CLI:

  1. At the command line, use the default system administrator credentials to log on to the system.
  2. To enable Session Reliability on HA failover, at the prompt, type: set ica parameter EnableSRonHAFailover YES
  3. To disable Session Reliability on HA failover, at the prompt, type: set ica parameter EnableSRonHAFailover NO

To Enable Session reliability on HA failover from NetScaler GUI:

  1. In a web browser, type the IP address of the primary NetScaler instance in the HA pair (for example, http://192.168.100.1).
  2. In User Name and Password, enter the administrator credentials.
  3. On the Configuration tab, navigate to System > Settings, and click Change ICA Parameters.
  4. In the Change ICA Parameters section, select Session Reliability on HA Failover.
  5. Click OK.

Limitations

  • Enabling this feature will result in increased bandwidth consumption which is due to ICA compression being turned off by the feature, and the extra traffic between the primary and secondary nodes to keep them in sync.
  • This feature is supported in Active-Passive mode only. Active-Active mode is not currently supported.
  • When HDX Insight is enabled, and Session Reliability on HA knob is set to NO, only ACR reconnect mode is supported in NetScaler high availability failover scenario. The HA knob does not disable Session Reliability if HDX Insight is disabled.

The Session Reconnect Semantics table is as follows:

Session Reconnect Sematics

Status EnableSRonHAFailover Yes EnableSRonHAFailover No (Default)
HDX Insight enabled Session reconnect for ICA Sessions works Session reconnect for ICA Sessions does not work
HDX Insight disabled Session reconnect for ICA Sessions works Session reconnect for ICA Sessions works

Points to note

  • Session Reliability for ICA sessions works out of the box with Gateway.
  • Session Reliability for ICA sessions does not work ONLY when both the following conditions are met:
    • HDX Insight is enabled
    • EnableSRonHAFailover is set to NO
  • Setting EnableSRonHAFailover knob to either YES or NO does not make any difference, when HDX Insight is disabled.

Session reliability on NetScaler high availability pair

June 17, 2019
Contributed by:  C

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