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Backup (disaster) Plan

Discussion in 'General Discussion' started by SonServers, Feb 23, 2005.

  1. SonServers

    SonServers Well-Known Member

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    Let's say I have two similar Cpanel servers running side by side in the data center with DNS clustered. I would have accounts split up fairly evenly over the two servers. Each server is quite capable of running with all the accounts on it.

    Next, let's say each night the Cpanel backups from one server are saved to the other.

    Now, let's say something bad happens to one server that is going to take more than just a couple hours to get it running again.

    The question I'm asking is what would be the best and quickest way to restore sites (and have them available) from the backup of the failed machine onto the running one?

    One way I was thinking, is to have both machines running with the "shared IP" set to something other than the main IP of the server. Then if one server went down, the shared ip of the down server could be moved to the running one. Would WHM let me go in and change the shared IP on the running server to what the down server was using? If so, the accounts could be restored to the same IP they were on before, which would mean no DNS update time. Will WHM let you do that . . . change shared IP's leaving the current accounts where they are and then setting up the restored accounts on a different IP basically resulting in two shared IP's on the server? One IP would have the existing accounts and the other would have the restored accounts from the down server. Would it be that easy?

    Another way I was thinking was running both servers with a low (15 min.) TTL on the DNS. Then accounts could be restored to the running server and in only 15 minutes after being restored, the DNS would be working on the new IP. I realize it would add a little load to both servers with that short of a TTL, but I wouldn't expect it to make a huge impact.

    Would there be an even better way? There is probably a better plan that I'm not thinking of. The idea would be to get the sites from the down server restored and working on the running server as quickly as possible.

    I will appreciate any ideas you may have.
     
  2. chirpy

    chirpy Well-Known Member

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    I haven't thought of all eventualities, but I will point out a couple of issues:

    1. Moving IP addresses obviously relies on your datacenter allowing you to do this.

    2. You can change the shared IP address in WHM, but you can only have 1 shared IP address, so once you change it all new or restored accounts will use the new IP address until such time as you set it back

    3. Using a TTL of 15min is pretty much pointless. Most ISP DNS servers will ignore such a low TTL and self-impose a 24 hour one. In the not too distant past some ISP's (notably AOL) used to use 72 hour TTL's regardless and countries on slow pipes even longer. Much of that has changed, but any TTL less that 24 hours cannot be relied on at all.

    Because of those issues, you're simply better off getting the second server fixed if it's going to take less than 24 hours.

    Whatever you do, make sure that you have two nameserver records for each domain with the DNS servers spread over two physical servers, preferrably in completely different datacenters.
     
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