This article contains information about the differences between the Surge Queue and Surge Protection features of the NetScaler appliance.

Background

Enable the Surge Queue feature on the NetScaler appliance by enabling the Surge Protection feature of the appliance. At times, this confuses the users to assume that both the features are the same. However, these are the different features of the NetScaler appliance.

Surge Queue

A Surge Queue is a path in the NetScaler appliance through which all client connections are sent, irrespective of the condition of the target service, such as service being loaded or service has reached the maximum connections state. When the number of requests to the servers is less, the connections are not observed in the Surge Queue because the connections are sent to the servers quickly and the Surge Queue build up is not observed.

Note: If the services reach the maximum connection state and there is a Surge Queue, some of the connections must be freed before the Surge Queue can reduce. If the connections are maintained for a long duration, you need to rely on the client timeout before the client knows that a reattempt is required to make a connection.

Surge Protection

The Surge Protection feature of the NetScaler appliance controls the acceleration of the connections in case of a surge in the network traffic. This feature uses the Surge Queue to hold the additional connections. The Surge Protection feature controls the number of users that can simultaneously access resources available on the back end servers. Additionally, this feature queues the additional requests as soon as the servers reach the respective capacity.

Note: You must not use the Surge Protection feature with Use Source IP (USIP) mode enabled. Additionally, the Surge Protection is done for each service but the threshold has a global value.