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How to switch Server?

Discussion in 'General Discussion' started by khorinis, Oct 26, 2010.

  1. khorinis

    khorinis Well-Known Member

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    Hello,
    i've got the following problem:
    I want to change the server. That mean i need to backup the entire customer account from WHM / Cpanel and put it onto the new server. Also i need a zero downtime. Is it able to order new server two days before the old one stop, prepare it (update OS, install cpanel - do i need a second license or could i put license of it later?) and then make a fresh complete (full) backup of the current server and then disable the current and enable license on new one and upload backup. Does that work or how to? I got 2 server (1 will end then - only 1 remain), 1 cpanel license and i need no downtime.

    The most important thing is that no email should be delivered to old server. If someone send an email to example@example.com - how does the email know which way it should use? If DNS it would use the wrong maybe for 1-2 days because of dns cache?
     
    #1 khorinis, Oct 26, 2010
    Last edited: Oct 26, 2010
  2. khorinis

    khorinis Well-Known Member

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    Please help me - it's important.
     
  3. cPanelJared

    cPanelJared Technical Analyst
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    No way to avoid downtime

    There is no way to completely guarantee zero downtime when moving from one server to another. Even if you prepare everything beforehand, in terms of copying your account data, there is still the fact that DNS data can be cached, and there is no way to totally avoid this.

    After you make the DNS changes, it is very possible for mail to be sent to the "wrong" IP address until the DNS changes propagate fully. Different providers' DNS servers update their caches at different rates, and some are very slow to update, so even if you do everything right, there is still the chance that some customers' providers will cache old data in their DNS servers, and this can take hours or even days to change.

    What you described in your original post will work in theory, but you are looking for a guarantee of zero downtime, and there is no way to make that guarantee, due to the caching nature of DNS servers.
     
  4. khorinis

    khorinis Well-Known Member

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    How does big companys prevent a such problem?
     
  5. twhiting9275

    twhiting9275 Well-Known Member

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    Jared is right here. It's theoretically possible to do this, but there are so many issues that are out of your control it's not even funny. Here's how I handle server transfers and moves, and it's worked PERFECTLY for me for a number of years, providing next to instant transfers:

    Step 1 - Cluster DNS between the two servers and copy all zones over to the new server. Make sure BOTH servers have the same copies of the same information before you start, and they both sync on changes, this is important.

    Step 2 - Change your nameserver IP addresses at your registrar. You can do this later if you want (ie: after all the transfers), but this way you've got a jump on things.

    Step 3 - After about 12 hours or so, start the transfers whm -> whm .

    While this won't exactly solve all of the caching issues mentioned above, I've found that those tips (coupled with using opendns) pretty much solve anything. What I do for larger sites with MySQL tables (ie: forums, wordpress, etc) is edit their config files to point to the local server temporarily, and move them one at a time after I'm sure the dns should be completely moved over.

    All said and done, you need to allow 1-2 weeks for this whole thing to take place. Usually, not so long, but it's still best to allow that time.
     
  6. bin_asc

    bin_asc Well-Known Member

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    You`d need to use Anycast DNS in order to avoid DNS caches, and ensure optimial, if not, 0 downtime caused by DNS.
    You`d also need to take in account that large files do take ALOT of time to transfer, especially if servers are in different locations, so getting from 1 to 2 doesn`t ensure you won`t loose posts for example.
     
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