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Website backup and nameservers

Is this possible and what are the best services around.

I have my own server. If it should fallover, can the website automatically point to a backup site. I take it i need a service that offers a second nameserver. Its a bit cloudy to me so any information will be greatly received.

Also, please explain how this works with exchange mail.
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sunny-j
Asked:
sunny-j
2 Solutions
 
Chris DentPowerShell DeveloperCommented:

For websites DNS won't help you for failover, unless you're changing Records to point to an alternate Web Server. That, in turn, would require you to set a very low TTL for the record meaning remote DNS servers would only cache the old response for a short time.

If you were to setup two records for the same server DNS would just alternate the response it gives. DNS itself isn't too bothered whether the server you're looking for is available or not.

Mail is a bit different. MX Records do offer failover / priority based delivery. DNS will, when queried, return the full set of MX Records for a Domain. e.g.:

<Email Domain Name>  <Record Type>  <Priority>  <Target Server>
somedomain.com.  MX 10  PrimarySMTP.somedomain.com.
somedomain.com.  MX 20  BackupSMTP.somedomain.com.

The SMTP Server sending to that will pick the server with the lowest Priority (in this case, PrimarySMTP.somedomain.com) and only attempt others if it cannot connect to that.

DNS itself doesn't actually pick the record the mail server gets in this case, it's just a convenient place to store Priority information for the Mail Exchanger record type.

Chris
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Malli BoppeCommented:
Agree with what Chris said. You would have some sort of downtime.Only solution is to have network load balancing cluster.But would need a another server and windows license for that.
http://technet2.microsoft.com/windowsserver/en/library/884c727d-6083-4265-ac1d-b5e66b68281a1033.mspx?mfr=true

More info back backup mx records
http://www.amset.info/exchange/smtp-backup.asp
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Adrien de CroyCommented:
Hi

There are several modes of failure in a web site, which need to be addressed in different ways.  The key ones are:
1. Link failure to the web server
2. failure of the web server itself

If you're only concerned with the second one, and you aren't worried about the DNS issues, then server virtualization is a really good way to get backups going.  Take a look at VMWare.  This will allow you to replicate your entire machine setup on another machine really quickly.

Anything that results in selection of different DNS records for failover is problematic for the TTL reasons (Time To Live) that Chris mentioned.  There are also systems that allow a number of machines to share a single IP address as well.  You then get micro-outages (~20s) with ARP from the router though (but this normally isn't a problem).

If you're worried about scenario 1, you need failover DNS servers, and links etc etc etc.
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