Double posting with load balancers

[alexi]

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?

[TECK]

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?

[Marco van Herwaarden]

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

[alexi]

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?

[Marco van Herwaarden]

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

[TECK]

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...