Citrix ADC

Request retry if back-end server resets TCP connection during connection establishment

December 1, 2020

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When a back-end server resets a TCP connection during connection establishment, the request retry feature forwards the request to the next available server, instead of sending the reset to the client. By doing reload balancing, the client saves RTT when the appliance initiates the same request to next available service.

How request retry works when back-end server resets a TCP connection on SYN establishment

The following diagram show the components interact with each other:

How request retry works

The process starts by enabling appqoe feature on your appliance.
When the client sends an HTTP or HTTPS request, the load balancing virtual server initiates connection to backend server.
If the requested service is unavailable on TCP SYN establishment, the back-end server resets the TCP connection.
If the appqoe configuration has “retry” enabled with the desired number of retry attempts specified, the load balancing virtual server uses the configured load balancing algorithm to forward the request to the next available application server.
After the load balancing virtual server receives the response, the appliance forwards the response to the client.
If the available back-end servers is equal or lesser than the retry count and if all the servers send reset, the appliance would respond a 500 internal server error. Consider a scenario with five available servers and the retry count set as six. If all the five servers resets the connection, then the appliance returns a 500 internal server error to the client.
Similarly, if the number of back-end servers is more than the retry count and if the back-end servers resets the connection on TCP SYN establishment, the appliance forwards the reset to the client. Consider a scenario with three back-end servers and the retry count set as two. If the three servers resets the connection, then the appliance sends a reset packet to the client.

Configure request retry (GET and POST method) when back-end server resets on TCP SYN establishment

The CLI and GUI configuration is similar to steps followed for GET and POST method. For more information, see Configure request retry for GET method topic, Configure request retry for POST method when back-end server resets a connection section.

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Request retry if back-end server resets TCP connection during connection establishment

December 1, 2020

Contributed by:

December 1, 2020

Contributed by:

Request retry if back-end server resets TCP connection during connection establishment

How request retry works when back-end server resets a TCP connection on SYN establishment

Configure request retry (GET and POST method) when back-end server resets on TCP SYN establishment

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