Using "predictor hash address" to maintain sticky sessions

Answered Question
Aug 16th, 2007
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I have a question about predictor.


We have two proxy servers balanced on the front end by a CSM. These servers then use a "backend" VIP to access two web/application servers. Each proxy server session must stay stuck to the same backend web/app server.


Because traffic has been evenly balanced on the proxy servers we used "predictor hash address source" to balance traffic to the web/app servers. Sticky connections could have been used but the predictor method was less complex and suited our purposes (traffic balanced evenly and sessions stayed stuck).


The proxy servers are changing from active/active to active/backup (obviously now there is no load balancing of the proxy servers). All traffic is now from a single source IP so therefore the "predictor hash address source" won't balance between the two backend servers.


My question is can we use "predictor hash address" to balance based on a hash of source AND destination IP? This will reduce the changes required on the CSM. My primary concern is that the traffic won't be balanced to the two backend web/app servers.


I know sticky groups can be configured for this but I want to keep changes to a minimum.




OLD SETUP ("predictor hash address source" balanced traffic to backend servers and "stuck" the sessions)


proxy: 10.1.1.1 or 10.1.1.2

CSM VIP: 10.2.2.2

Backend web/application servers: 10.3.3.3 or 10.3.3.4





NEW SETUP ( Will "predictor hash address" still balance traffic to backend servers and keep sessions "stuck"?)


proxy: 10.1.1.1

CSM VIP: 10.2.2.2

Backend web/application servers: 10.3.3.3 or 10.3.3.4


Correct Answer by Gilles Dufour about 9 years 11 months ago

if the src is the same 10.1.1.1 and the destination also always the same 10.2.2.2, I don't see how you can maintain stickyness and also loadbalance the connection between 2 servers.

Only a cookie would let you identify the real source of the traffic [ a client ] and split the connection from the single proxy to different servers.


Gilles.

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Correct Answer
Gilles Dufour Fri, 08/17/2007 - 00:10
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  • Cisco Employee,

if the src is the same 10.1.1.1 and the destination also always the same 10.2.2.2, I don't see how you can maintain stickyness and also loadbalance the connection between 2 servers.

Only a cookie would let you identify the real source of the traffic [ a client ] and split the connection from the single proxy to different servers.


Gilles.

glnmaster Fri, 08/17/2007 - 05:16
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Hi Gilles,


Thanks for the quick reply. Time to break out the milk!



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