Irule to LB traffic based on least connections

There is a least connections load balancing algorithm for LTM and GTM. You can get more info on these modes in the config guide for your version on Askf5.com. I would think that you could specify a persistence method on GTM to ensure requests make it back to the correct datacenter, and then use a persistence method at the LTM level to ensure requests make it to the correct app server. Have you tried this yet?

 

 

Aaron

 

 

Yes this is in place already, the real issue revolves around cached DNS responses by mega proxies. The GTM has a wide IP for each location pool and are balanced using round robin. Each pool has a DNS A record. There are 5 pools at each location and the pools are balanced using least connections. Once a mega proxy (such as AOL) caches a DNS response then everyone making a connection from AOL will go to the same pool, thus overloading the APP servers behind the web apps. What I am looking to do is basicly re-balance the connections with an iRule rather than using the default pool.

What criteria would you want to use in an iRule to break up the AOL users?

 

 

If the major issue is that when you treat anyone coming from AOL subnets as a single client the web servers get overwhelmed, you could try disabling the mapping of AOL clients on the LTM's. Assuming you use cookie-based persistence on the LTM's, you would get an even dispersement of requests at the server level. Of course, you'd still potentially run into issues with one datacenter receiving all of the AOL requests. But I don't really see a way around this if you need to treat all AOL users as one for persistence at the datacenter (GTM) level.

 

 

Aaron

It's not just AOL but any ISP that uses a mega proxy or caches a DNS response longer than the configured TTL. The iRule that is deployed is using session persistance to the pool that it was assigned based on the load balance scheme we have configured. If a new connection is made and does not have a cookie it is then sent to the default pool so if by chance the connection is coming from an ISP that has cached a specific DNS response for a pool the connection is sent to that pool. I know this is normal behavior and out of our control, the real issue is the application not keeping state information in the database. So until the delvelopers come up with a solution to their problem we have been asked to try and fix it using the load balancers. I guess the bottom line question is; Does the GTM/LTM store information about least connections somewhere and if it does can an iRule be used to make a decision based on this information? If it is possible what would the impact be on the LTM's if we have almost every connection go through the load balance process essentialy a second time.