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stuartwevansuk_'s avatar
stuartwevansuk_
Icon for Nimbostratus rankNimbostratus
Mar 02, 2014

F5 GTM Persistence & LDNS

Hi,

 

Can anyone help with DNS persistence? we run an e-commerce app out of 2 DC's with a GTM in each supplemented by a pair of LTM's, our app requires session persistence for the lifetime of a transaction, user browsing, adding contents to their basket and ultimately checking out.

 

I've started seeing numerous reports about persistence issues on our sites (users being logged out, losing baskets), we have static persist at the WideIP level but we are still seeing numerous reports of lost sessions etc. I can only see that this is possibly down to LDNS servers changing mid transaction (aren't most LDNS servers load balanced in some way?).

 

Is there anything that can help to resolve our issue?

 

Cheers,

 

application delivery
availability
BIG-IP DNS
design
gtm
microsoft

3 Replies

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  • IheartF5_45022's avatar
    IheartF5_45022
    Icon for Nacreous rankNacreous
    Mar 03, 2014

    Hi - unfortunately if you are using an internet-facing application there is no way you can guarantee that an LDNS will stay the same during the lifetime of a user session. GTM persistence or static persist will only get you approx 70-80% (in my experience) of HTTP requests hitting the same site :-(, however this is better than 50/50 - you only need to deal with 20-30% of sessions at the wrong site.

     

    If using some kind of inter-site session store (like memcached) is not an option and the session really need to be server persistent, then you'll need to create access from the LTMs of one site, to the servers of the other, either using backend WAN links, or t'internet, either with or without a WOM product.

     

    Once you have the inter-site access setup, you can use priority-group activation to include the servers of one site in the LTM pools of the other site (and vice-versa). There are other ways to deal with this (like site-specific HHTP redirection), however the latter option I describe has worked well for us.

     

  • Laudec's avatar
    Laudec
    Icon for Nimbostratus rankNimbostratus
    Aug 05, 2014

    Perhaps as a solution on the static persist method, especially if the client LDNS change mid session, is to change the 32bit mask to a 16bit mask perhaps in the configuration.