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Faster DNS Load Balance

Posted on 2012-04-03
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Last Modified: 2012-04-24
I am looking for a solution to have better up time for my web server that we are hosting locally, Right now our main concern is losing connection to our ISP provider so we have a separate connection coming in from a different provider. My domain name for the website is hosted with a third provider, now what I am trying to do is make it possible that if my main t-1 went down the users request could recognize that the IP address in the first DNS entry is down an reroute the user to the second IP in the DNS entrée for the domain name. Both IP address point back to my web server but I can’t figure out how to make this work without flushing DNS from the PC that is trying to access the Website, any ideas?

Thanks
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Question by:ahmad1467
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by:Papertrip
ID: 37803014
Round robin DNS (multiple A records for same label pointing to different IPs) is not capable of doing what you are requesting.  DNS does not know or care if anything responds at a given hostname or IP.
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Papertrip earned 500 total points
ID: 37803063
I would keep the TTL on that RRset not too high and not too low... 5-10 minutes.  I imagine by that time you would be notified of the link being down and can then remove the down IP from DNS and won't have to worry about resolvers having the down IP cached for an extended period.
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by:ahmad1467
ID: 37803173
This site is a web site that we really could not afford to have down do you know if there is a way to make this seamless and make this change quickly?
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by:Papertrip
ID: 37803208
Do you have any sort of notification when the link is down?  Do you have any network load balancing or something similar between connections?  I'm not a network guy but something might be able to be done depending on your network config between the links.  Create a VIP with a single public IP that points to the 2 web server IP's and can monitor the port and take action on it.  But again I don't know how your network is setup and am not a network admin.  Of course then if the provider that is serving the IP of the VIP goes down then you're down again anyways.  That is all kinda out of scope for this question.

You could script a monitor that either pings the IP's or perhaps does some sort of GET request which then dynamically updates your DNS zone depending on the status of each IP.  That of course requires scripting knowledge and the ability to dynamically updates your zones.
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by:Papertrip
ID: 37803220
If you can't afford to have the site go down for 10-20 minutes until you are able to manually update DNS during a major network event, then I suggest hosting your website elsewhere or using a CDN such as Akamai depending on your business needs.

I'm saying this aside from your current question.  There are many other things just waiting to go wrong if you are locally hosting a website that needs such high uptime.  Have you considered hosting offsite?
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by:xcomiii
ID: 37804731
If you cannot afford to have downtime on your primary provider, you have to setup a router/firewall on your network that supports BGP, and setup BGP with both your providers. That is not a walk in the park and requires some configuration changes on both ISP's. And you also need to apply for your own ISP-independent IP addresses.  

BGP is much more complicated than other routing protocols, but very robust and it provides an instant fail-over without any drop of connection for clients. BGP is also the backbone of internet and what really makes internet work like it is today.

Oh, and did I mention it is an expensive solution? The cheapest firewalls that support BGP, starts from around 1000 $. And you probably have to pay for the work hours at both your ISP's, plus your own time.
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