F5 GTM Persistance

Wow, great topic. You have cut right to the heart of the matter. We have been trying to get the same behavior from our GTM/LTM hardware ourselves, and really haven't been able to overcome the inherent limitations of DNS persistence without building something rediculously expective/complex. What may be a bit different is that we are actively trying to load-balance between a couple of data centers instead of using one entirely as a DR facility.

 

 

I think Hoolio's explation is great for a high-level understanding. But when it comes down to it, the GTM can only load-balance DNS requests that it receives. And unfortunately the way DNS was designed, DNS requests aren't made by end-user machines - they are made by other DNS servers. You may get a client whose primary DNS server is in one IP range, but their second DNS server in a completely different range. The GTM doesn't know this - it simply sees two different requests from two different IP addresses. The GTM has no way to figure it that it is really the same end-user device asking for the name.

 

 

And that's one simple scenario - they can become more complex when you consider how other companies may manage their infrastructure. You, as a GTM admin, have no way to control this.

 

 

That being said there are ways to mitigate the effects of these limitations, but no where near 100% effective.