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The F5 GTMs automatically reroute users to one of the available datacenters should one fail. How does it do this? For instance the F5 could act as a DNS server and simply serve a different IP to clients but how would it get around caching?

I'm interested in this because I'd like to see whether obtaining this sort of availability is possible with open source tools that could be coded to do similar stuff

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The F5 GTM does its load balanancing ENTIRELY with DNS. GTM doesn't do any physical routing of traffic.

It has a massive set of health checks it can perform on hosts, on services, or on groups of services that are tied together as "distributed applications" and when any of these fail, it uses DNS to reroute to the right place

In terms of getting around caching, you set your TTLs very low (10-30s) so that you minimize effects of folks hanging onto IPs.

Have a look at this article for a discussion of open source alternatives to F5 BigIP:

https://devcentral.f5.com/Community/GroupDetails/tabid/1082223/asg/52/aft/1178927/showtab/groupforums/Default.aspx

I've been happy with our F5 GTMs and LTMs so far, but they're indeed expensive.

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Just to note, there seem to be two different strategies here using open source solutions. One is using GeoIP info (with bind for instance) for the user's source address, and the other is relying on BGP information (Super Sparrow for instance). –  mbrownnyc Jan 6 '13 at 19:26
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its most likely due to a heartbeat between the devices. we use radware for our load balancing, but were not doing it across the internet cloud, we have a private connection between our radware devices.

if you have a test enviroment, try inlab's balance product. its a gpl licensed.

hope this helps! :)

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Thanks. I run hearbeat2 across mine. I was wondering whether there was extra "magic" concerning the gtm. For instance local balancing in global data centres and detecting failure. It could be that they don't really do that but they seem to. –  Stewart Robinson Jul 30 '11 at 8:22
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