Site redundancy

sewebman

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Joined
Nov 8, 2003
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Location
Thomasville, GA
If I have a domain that I want to virtually guarantee uptime, do I need more than one hosting account with different providers?

Also, if I did that, I know that I can use multiple DNS servers at my Godaddy account, but is there any other set up required with either host?

Do I have to do anything special with email. For example, do I set up pop3 accounts for both hosting accounts?

Thanks,

Jim
 
Hello,

You could simply setup one account on each server as normal, then add 2 A records wherever your DNS server(s) is/are located, pointing the two duplicate records to each of the 2 accounts.

As for email, if you wanted to pick one server to control the email, you'd just set the MX record to a domain that only exists on the server you want (ie, only use 1 mail A record and set the MX to mail). The email system is pretty good at waiting for a server to be up if its down. (or just have 2 MX records and have the other server forward to the first one).

John
 
DirectAdmin Support said:
You could simply setup one account on each server as normal, then add 2 A records wherever your DNS server(s) is/are located, pointing the two duplicate records to each of the 2 accounts.
As has been discussed many times on the bind-users list, this does not give redundancy.

It gives you some load balancing, as the nameserver will give alternate A records each time it's called.

But it will continue to do that even if the server the A record is pointing to is down, with rather complex scripting (done outside of bind) to check the server every minute or so, and if it's down, then remove the A record from the zone file and reload the bind zones. (It also requires a quite short TTL, perhaps under five minutes.)

A much better way (that will give both some load balancing and redundancy) is this way:

1) two webservers hosting the account

2) Each server hosting not only the website but the DNS

3) Each webserver providing only A record for itself.

4) Registry (where the domain is registered) listing both nameservers

5) Again, very short TTL.

The way DNS works, is when someone tries to find the site, both nameservers will be returned, and queried.

The local user's computer will use the DNS record s/he gets back first, and will then point to the site in that A record.

If the server goes down, the DNS goes down with it, and only one DNS server will return a response, and it will return the A record it hosts.

There's a problem with this method as well; most browsers don't clear DNS until they're shut down, so if you're looking at the site and it goes down you'll have to restart your browser before you can see it again.

There are other ways that are more foolproof, but they require rather complex and expensive solutions.

For example, this is precisely what Microsoft's Active Directory does; it separates servers from their DNS records. Of course if the Active Directory server goes down, you're still dead in the water :( .

Jeff
 
sewebman said:
If I have a domain that I want to virtually guarantee uptime, do I need more than one hosting account with different providers?
Yes, and do a few other things besides; see my response to John.
Also, if I did that, I know that I can use multiple DNS servers at my Godaddy account, but is there any other set up required with either host?
Your provider must supply DNS, and s/he must be willing to give you a very low TTL (time-to-live) on your DNS.
Do I have to do anything special with email. For example, do I set up pop3 accounts for both hosting accounts?
Not recommended, as your users would then have to log into both locations to get their mail.

As John points out, you could just ignore it; email will be held on the sending server until your server is up again. For most servers it keeps trying for four or more days (7 by default with DirectAdmin if I recall correctly), though some servers (most Sendmail servers by default) will notify the sender after 4 hours if the mail still hasn't been delivered.

Backup MX, as mentioned by John, is a great idea that loses most of it's functionality in today's world. First, you'd have to specify one of your hosting companies as the primary MX and one as the backup MX, and your backup MX provider would have to make certain changes to his mailserver files to enable it to work properly for you. Note that while spamassassin can be configured to work for backup MX, it's not trivial to set up (there are even arguments on the spamassassin list as to how to do it.

We recently decided to not offer backup MX as a generic service for just that reason.

We do have a lot of experience with these kinds of solutions and host a major Credit Union, a movie studio and a few other sites that require this kind of redundancy. John doesn't like mentioning prices on this forum and I'm not trying to sell you anything, but I hope he won't mind me pointing out that these solutions can easily cost hundreds to thousands of dollars per month, especially when sites use databases in realtime.

Jeff
 
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