Double posting with load balancers
 

We just recently switched to load balanced web servers and all of a sudden I am seeing a bunch of double posts. I wondered if anyone has seen anything like that before?

You basically didn't tell us nothing. :)
What is your exact setup (software and hardware)? How do you mirror your data?
Are you using a worker-proxy setup?

Posts (ie. data) are stored in the database. Source of your problem is more likely the MySQL setup then the webserver setup.

That's kind of what I was thinking Marco. The front end is just 2 webservers with a hardware load balancer, nothing special but it's the only recent change I can think of. Are there any specific mysql parameters that would make double posting more likely?

Nothing that i can think of atm. Can you post a bit more details about your server setup.

alexi, since you do not want to post your exact server configuration, I'm going to guess.
Double posts happen when your current Unix setup traceroute dies on a specific hop. More exactly, if you run a traceroute and you get a request timeout. That is the critical moment when you could have a double post initiated... because the data is transmitted in bits.

So it is very simple to solve your problem. Run a traceroute and see how is your response. You will be able to identify right away if you are dealing with a heavily congested network, an error in the routing table or a faulty connection. After you have determined the bad location, you will need to use a utility such as ping to continue troubleshooting.

EDIT: I could resume the above posts to:
Hi, my car is not working. What do you think is wrong?
Well, it could be either the engine or the transmission.
Aha, I thought so, so what do you think is broken?
I don't know, maybe you could start by telling me what is your make and model...