F5 GTM DNS persistence

We ran for about 8 years with a dual site load balancing architecture for our Internet accessible web sites. Started with 3DNS engines and BigIP at version 3.x, thru 4.5, now at version 9.48 GTM and LTM. We used persistence at the DNS level and simple source ip persistence at the LTM, or BIgiIP level. That worked fine for the first few years until the load balancing of local DNS servers started happenign and it started to become more common for a users ldns to change during the middle of their web session. That could be alleviated by increasing the TTL, but the tradeoff is more downtime to a user if you have a problem at one datacenter and they keep coming to it until the TTL expires and they ask you again which datacenter to go to.

 

 

As a stopgap we applied topology records that basically split the Internet in half, and went with a quasi active/standby for each half, making each datacenter primary for one of the halfs. That seemed to work fairly well. It was still technically possible for someone to be using an ldns from the lower half if the IP range and then come from one in the upper range, but it was much less likely.

 

 

We then (about 2 years ago) closed our second in region datacenter and moved a lot of the equipment either to our one remaining datacenter in the region, and opened an out of region datacenter about 1500 miles away. The latency involved with that connection made a lot of the apps unusable when the app servers were in the out of region datacenter and the database was in the primary, so we are in a true active standby mode now.

 

 

I have read some of the stuff F5 is coming out with on global topology to try and address the issue of ldns persistence, but haven't had the time to pursue it yet, although we are starting to get more pressure to make use of the valuable resources in our out of region datacenter for more than just insurance against a disaster, so I'm going to need to make the time....

 

 

Regards,

 

 

Mark