Minimizing Downtime When Switching IP Addresses?

GeekTek asks: "As we all know, prices for co-location have plummeted since the height of the dot.com era. We've been shopping around and found a solution that works for us. We have a small setup of about a dozen Debian boxen, a few Windows servers and we run our own name servers (BIND 8.x). Most of our domain names are managed through our OpenSRS account. My concern is switching all of our server's IP addresses. I can not have any down time and I want to minimize the number of trips to the current co-lo (it's >2 hours away). What is the best way to do it? What experiences can you share in similar situations?"

Comments

Reduce TTL

[linuxwrangler]

Start reducing your DNS time-to-live. If it is now a week, set it to a day. A couple of days ahead set it to an hour. A few ours ahead set it to 5 minutes (do consider your traffic and make sure that you won't swamp your DNS server - if you are planning a move at night then load should be low and even setting ttl to a minute or two should be fine). Note: there are broken name servers out there and you will get requests to the old address for many hours. Also most browsers don't seem to ask based on DNS TTL so they may not get the new IP until they at least leave your site or perhaps close their browser.

(Note: I'm assuming you have duplicate equipment since that's the only way to physically move with no downtime unless your configuration allows you to remove half of your stuff and still keep running.)

Depending on your needs and current design you can also play NAT/Proxy games. Ie. set up a proxy server or use NAT to make your old IP contact your new servers to catch all the misdirected traffic until DNS propogates.

Last couple of times I did this it was fun to watch. I pulled the trigger on the DNS and could watch the load flow from the old to the new site (we were in the top 500 sites in traffic and did the move during the day so there was a statistically valid sample to work with).