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Quickly Switching Your Servers to Backups?
moogoogaipan writes "After a few days thinking about the quickest way to bring my website back to the internet users, I am still stuck at DNS. From experience, even if I set the TTL for my DNS zone file as low as 5 minutes, there are still DNS servers out there won't update until a few days later (Yeah. I'm looking at you, AOL). Here is my situation. Say that I have my web servers and database servers at a remote backup location, ready to serve. If we get hit by an earthquake at our main location, what can I do in a few hours to get everyone to go to our backup location?"
Same Provider at both (N) locations, Same IPs for servers/services, Just don't advertise the prefixes via BGP from the backup location until the primary one goes down.
Talk to your ISP. They can set it up so the IP addresses at the main location can be rerouted to the DR site almost instantly.
You could spend a bundle of money doing global load balancing and maintaining a full hot spare site, or you could figure out how critical it really is that your website be up within 5 minutes of some major disaster like an earthquake.
In the event of a major disaster, the need for "immediate" recovery is actually defined as being able to be back up and running within 24 hours of the event. This is true even for business critical functions. Unless your business would cease to exist within 24 hours if your website went down, I would consider a 72 hour return to service to be perfectly adequate, and it would cost a whole lot less time and money to set up. Keep in mind that we are talking about an eventuality that would only occur if your primary site was entirely disabled for an extended period of time, which is highly unlikely to happen if you're hosted in any kind of modern data center.
Depending on the industry, that's a very real problem.
Sysadmin: "Don't worry, we're already switched over to the hot spare, just get out of there!"
CIO: "What if the whole building goes?"
Sysadmin: "No worries. Remember that $1M we spent stringing all that fiber over to the other datacenter?"
CIO: "Oh yeah, the one in WTC 2!"
Sysadmin: "Aaw, shit."
We have used DNS failover from dnsmadeeasy.com for a couple years and have put it to the test a couple times. They have had perfect reliability and a low cost (typically well under $100/year).
The method is not perfect, but it is plenty good enough for our needs to protect against something that takes a datacenter down for a prolonged time (several minutes/hours/days). And the price
And to those who recommend avoiding "disaster prone" places: they all have people. People like the backhoe guy who took out the OC192 down the street. Or the core drillers who managed to punch both the primary and secondary optical links to a building of ours at a point where they were too close to each other.
You can roll your own by having a DNS server at each site and DNS 1 always issues IP of server 1 while DNS 2 always issues IP of server 2. But there are a number of issues like traffic hitting both sites at the same time. And you will have to detect more than just a down link so you will be scripting web test and DNS update systems. By the time you are done, you will have spent decades' worth of dnsmadeeasy fees.
Note: dnsmadeeasy isn't the only game in town. Just the one we happen to use.
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"You are not remembered for doing what is expected of you." - Atul Chitnis
For a real answer, buy Theo Schlossnagle's book, "Scalable Internet Architectures". Theo presented a lengthy and highly-informative session at OSCON last year, and I subsequently bought and read his book. Worth every penny if you're professionally involved in providing reliable Internet services of any kind.
you may find that people have other things on their minds when that amount of shit hits the fan.
Really interesting point that seems to be overlooked. The CEO is concerned about getting everything back up and running (since statistically they have no heart or pulse), but the employees are more concerned about finding family members in the wreckage of their house, cleanup, watching the kids cause schools are shut down, etc..
Whatever you do, ensure it is automated as possible, and please, please, please don't forget to test. I've heard to many stories about everything looking okay, until the emergency generator runs for several hours, vibrating a connection loose and causing it to shut down. It would pass the test run every month, that was only 15 min long. "Hmm, power is out, and power poles are blown all over the streets, do I stay safely inside? Or do I brave a trip across town to try to flip a switch for my wonderful employer?"
What are we going to do tonight Brain?
Hi, An alternative is to forget the all-or-nothing view, and make sure that with some simple round-robin DNS and enough geographically-separated servers for the DNS and HTTP/whatever, then even if one is taken out by a quake or Act of Congress (ewwww, those nature programmes), *most* users will still get through just fine. Any clients/proxies that are smart and that can try out multiple A records for one URL will always get through if even one of your servers is reachable. Example: my main UK server failed strangely yesterday morning, but only about 30% of my visitors can even have noticed, and the other servers worldwide took up some of the load. Just simple and reliable and cheap round-robin DNS. Rgds Damon
http://m.earth.org.uk/
The industry pros discuss this sort of thing there all the time. The colocation sub-forum would be the best place to ask. I know that sounds odd, but that's the area on WHT where the best network/transit/BGP people hang out.
Nothing is inexplicable; only unexplained -Tom Baker, Doctor Who
When $ is no issue, a tier 1 colocation provider with their own services would be the best option. They've got big pipes, and will work with you to have the additional services needed. I'd go as far to say that you're going to want to have a failover script that they would follow in the event of site A going offline. You'd need redundant equipment, or use a DR firm for getting back up.