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I have a webserver. I have 2 static IP's from 2 different ISP's. I want to make sure my webserver is accessible when one ISP's network(s) are down.

for example

my host name a.example.com
my ISP1 IP : x.134.x.100
my ISP1 IP : x.10.x.10

Current A records in my DNS for example.com.

a.example.com x.134.x.100
a.example.com x.10.x.10

My firewall routes both requests to same server and this works fine.

My question is

"Is it the right solution for problem? If not what is the right solution?"

EDIT: I saw this link http://www.linuxquestions.org/questions/linux-general-1/multiple-a-records-in-dns-734680/

Now my question is : What is the easy/cheapest way to provide high availability?

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Given your new question, I think we will need more details. What risk are you trying to mitigate with an HA solution? Power failure, network, web application, etc. requires different solutions. –  jeffatrackaid Dec 19 '11 at 19:02

1 Answer 1

The problem with this solution is that DNS will continue to hand out both IP's even if one server/ISP is down which means it won't really accomplish your goal. If you really need a true backup site, the best way to do this is to setup BGP.

It's a process, but you work with your ISP to setup a BGP router at each site advertising your public network. When one router or ISP goes down, it's a matter of seconds for the backup router to begin advertising your network from the backup site. No DNS changes, no waiting for anything to timeout or clear - it just works.

EDIT** Add secondary solution.
If setting up BGP is simply too far out of reach due to budget or some other constraint, I would recommend you setting up a DNS server at each site with a very short TTL (like 10 minutes assuming you don't have a HUGE amount of traffic). On each DNS server, create a single A record with the IP of the server in that site. So, in site A, configure a host record with the IP in site A and in site B create one with the IP in site B. This way, when the ISP goes down, you will no longer be serving out IP's that are unavailable.
Keep in mind with this solution, you will have clients that have cached the "bad" IP and they will have to wait for that to timeout before they will put the "good" IP from the other DNS server.

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Can you provide some link for detail understanding. From my experience, usually people at ISP support do not understand this.. –  Manjoor Dec 19 '11 at 13:26
    
BGP is complex so I can't really give you a single link that will cover everything you need to know. You will need to do some googling and some homework. Global Knowledge and other training co's have courses specifically for this. –  Paul Ackerman Dec 19 '11 at 13:33

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