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  1. #1

    Exclamation Help me have a "backup" webhost if my main goes down!

    Hello,

    I'd like to know how to do the following:

    I have a website with domain registration with Godaddy. I would like to host the *same* site on two different hosts, so that when one goes down, the other one is a backup that shows immediately. So basically, both of my hosts have to be down at the same time for people to not see anything on my site.

    I tried to do it by specifying the nameservers for both hosts in Godaddy, but that didn't work.

    Is this possible? How do I do this?

    Thanks very much in advance!

  2. #2
    I think you have ta add the nameservers of the first host as the the first 2 nameservers and the nameservers of the second host at the third and forth name server
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  3. #3
    Join Date
    Feb 2005
    Location
    Australia
    Posts
    5,849
    What you're looking for is called dns failover. It won't give you 100% reliability but it does give you a fairly quick fix in the event of major downtime at one host, and it's a great way to keep regular backups!

    The key point to remember is that all your nameservers must provide the same information. When the primary host becomes unavailable you change the information they provide to send traffic to the backup host. So you need to monitor both hosts and change dns records as necessary.

    The easy way to achieve this is to use a dns service like zoneedit or dnsmadeeasy. It's more difficult (but to me, more rewarding ) to set up monitoring yourself and change over your own nameservers.

    Either way, the limitation is that dns records don't update instantly. You can set a short TTL (time to live) but some ISPs are said to ignore this and cache records for longer. So after failover most of your visitors will be sent to the backup host within a few minutes but for others it may take hours.

    For a static site that's it. If you have a dynamic site then sending visitors to 2 different servers presents another interesting challenge: how do you deal with updates that may happen simultaneously on both servers? The usual answer is to have the primary read-write and the backup read-only, which is a bit of a limitation on the failover ideal but does ensure no data loss. Depending on the type of site you may be able to take a less conservative approach.

    HTH
    Chris

    "Some problems are so complex that you have to be highly intelligent and well informed just to be undecided about them." - Laurence J. Peter

  4. #4
    Join Date
    Aug 2005
    Location
    Canada
    Posts
    862
    You may want to read this thread.
    http://www.webhostingtalk.com/showthread.php?t=553551

  5. #5
    Quote Originally Posted by E.Emile
    I think you have ta add the nameservers of the first host as the the first 2 nameservers and the nameservers of the second host at the third and forth name server
    That's what I did, but it doesn't work. It doesn't automatically switch to the third and fourth nameservers.

  6. #6
    Quote Originally Posted by foobic
    What you're looking for is called dns failover. It won't give you 100% reliability but it does give you a fairly quick fix in the event of major downtime at one host, and it's a great way to keep regular backups!

    The key point to remember is that all your nameservers must provide the same information. When the primary host becomes unavailable you change the information they provide to send traffic to the backup host. So you need to monitor both hosts and change dns records as necessary.

    The easy way to achieve this is to use a dns service like zoneedit or dnsmadeeasy. It's more difficult (but to me, more rewarding ) to set up monitoring yourself and change over your own nameservers.

    Either way, the limitation is that dns records don't update instantly. You can set a short TTL (time to live) but some ISPs are said to ignore this and cache records for longer. So after failover most of your visitors will be sent to the backup host within a few minutes but for others it may take hours.

    For a static site that's it. If you have a dynamic site then sending visitors to 2 different servers presents another interesting challenge: how do you deal with updates that may happen simultaneously on both servers? The usual answer is to have the primary read-write and the backup read-only, which is a bit of a limitation on the failover ideal but does ensure no data loss. Depending on the type of site you may be able to take a less conservative approach.

    HTH
    I'll look into those. So you are saying that there is no way to redirect to the other host instantly if the first goes down?

  7. #7
    Join Date
    Feb 2005
    Location
    Australia
    Posts
    5,849
    There is a way, see for example http://www.linux-ha.org - but cost is several orders of magnitude higher than this. If you're talking about 2 different shared hosting plans then there's no way to achieve instant redirection.
    Chris

    "Some problems are so complex that you have to be highly intelligent and well informed just to be undecided about them." - Laurence J. Peter

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