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Round Robin DNS and Session Cookies- Will this work on a web server?

Posted on 2009-06-29
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Last Modified: 2013-12-14
Hi there,

We are looking for a simple way to add redundancy to a web app.
We are concerned about session cookies.

If we just put each server on a round robin DNS service, will that be sufficient at least for our beta release or will session cookies be a big issue?

I'm guessing that the user caches the DNS of the server and in such a case I would expect that problems are rare. But I could imagine that when they are on the site for over 15 minutes (assuming the DNS refresh is set to 15 minutes) then it will cause big problems.

IDEALLY: Is there a round robin DNS service that is designed for failover and will always redirect the same IP to the same server?

As a work-around, we are thinking: Since we have a centralized database, we centrally save all session data. Then, when a user without a session cookie is found, we check if it exists and log them in.
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Question by:the_cyman
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PaciB earned 500 total points
ID: 24737448
Hi,

In the Microsoft world what you're looking for is called NLB cluster (Network Load Balancing). That's the way I would reach the goal if the Web servers are Miscrosoft IIS servers.

I don't know much about non-microsoft worl but surely DNS round robin will not do the job because when you DNS client cache expires you could be routed to a web server that doesn't know anything about you current session (except if you have a process inside your application that can replicate session contexte between web servers).

When you configure NBL cluster you can do thing so that one client IP address will always be routed to one NLB cluster node.

Have a nice day
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by:bevhost
ID: 24742260
If the cookie session data is stored in a central database, I don't see how it matters which front end server processes each of the http: requests?

You can use BIND 9 DNS server to always hand the same IPs out to selected clients but that's not really round robin.
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by:Colin_A_Moulder
ID: 24743232
What I would use is Microsoft NLB and Distributed File System to point towards a central depository of web files that can also be updated concurrently.
As for session cookies, it is not an issue because you will be contacting the websites via the NLB cluster address and using host headers.
 
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by:the_cyman
ID: 24817743
Great, thanks guys. Looks like there are services like this one:
http://www.autofailover.com/
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