Report On Viability Of Domain Name Server (DNS) Failover Solution
Jun 22, 2006
I run a site with about 1,000,000 unique visitors per month and recents server failures made me decide to get a failover server to minimize downtime. My goal wasn't to get 99.999% uptime but to be able to be back on track after a failure in a "reasonable" amount of time. After evaluating several solutions, I decided to go with DNS failover. Here's how the setup work:
1) mydomain.com points to main server with a very low TTL (time to live)
2) failover server replicates data from main server
3) when main server goes down, mydomain.com is changed to point to failover server
The drawback is the DNS propagation time since some DNS servers don't honor the TTL and there is some caching happening on the user's machine and browser. I looked for empirical data to gauge the extent of the problem but couldn't find any so I decided to setup my own experiment.
The Experiment
==============
I start with mydomain.com pointing to the main server with a TTL of 1800 seconds (1/2 hour). I then change it to point to the failover server which simply port forwards to the main server. On the main server, I periodically compute the percentage of requests coming from the failover server which gives me the percentage of people for which the DNS change has propagated.
I made the DNS change at exactly 16:04 on 06/21/06 and here are the percentage of propagated users:
06/21/06 16:00 0 %
06/21/06 16:05 3 %
06/21/06 16:10 20 %
06/21/06 16:15 37 %
06/21/06 16:20 59 %
06/21/06 16:25 69 %
06/21/06 16:30 76 %
06/21/06 16:35 80 %
06/21/06 16:40 86 %
06/21/06 16:45 90 %
06/21/06 16:50 91 %
06/21/06 16:55 92 %
06/21/06 17:00 93 %
06/21/06 17:05 94 %
06/21/06 17:10 94 %
06/21/06 17:15 95 %
06/21/06 17:35 95 %
06/21/06 17:40 96 %
06/21/06 17:45 97 %
...
06/22/06 10:40 99 %
So even after 18 hours, there is still a certain percentage of users going to the old server so DNS failover is obviously not a 99.999% uptime solution. However, since more than 90% of the users are propagated in the first hour, the solution works well enough for me.
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Jul 13, 2007
I am trying to do a fail over solution with round robin dns. Our dns is served by windows and our web servers are setup with Linux..
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<< Removed Examples >>
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ns1.mynameservers.com
ns2.mynameservers.com
ns3.dnsmadeeasy.com
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ns5.dnsmadeeasy.com
ns6.dnsmadeeasy.com
Correct?
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May 1, 2008
Basically have 2 hosting accounts at different providers...each set-up for the same domain name...and then somehow wtih DNS make it so if host #1 goes down traffic goes to host #2 (which would basically be a splash screen explaining that host #1 is down and will be back soon).
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It wouldn't be as simple as setting the nameservers like this would it?
ns1.host1.com
ns2.host1.com
ns1.host2.com
ns2.host2.com
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Dec 10, 2007
Assume, a DNS failover service would change the DNS from server 1 to server 2 when the first one is offline. This will be changed quite fast, however isn't it true that some visitors still experience a downtime of a couple of hours (saying that the main server will be offline for 6 hours) as their ISP might not update DNS that frequently?
So basically, what is the added value of a failover service?
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Jul 22, 2008
What happens if your primary nameserver goes down? Meaning that it goes completely off the net, not even denying dns requests but completely ignoring them.
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Jul 8, 2007
I was wondering what sort of systems have you guys implemented for ensuring your website remains online.
Iv attached a pic of what I think are the best options.
What do you think?
Also, am I correct in my assumptions about DNS?
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