Redudncy DNS

joe2bron

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Mar 1, 2004
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Hi,
We have two reseller account on two different hosting services.
We know how to configure DNS that will have a domain on two hosting. This configuration, when we put the other hosting IP and configure the domain on the second hosting create a "ping-pong" situation. The visitor can get the first or the second hosting. We want to be able to have one major hosting, and only when this major one is down, then the other one will be available to the visitor.
Any suggestion how to configure ?
Thanks
Joe
 
Hello,

If you find out, let me know :) .. As far as I know, the round robin method is as good as it gets (ping pong). Not sure that bind has an active method of checking if things are down. Maybe some bind experts know.

John
 
This is a way in (not necessarly in BIND) some DNS servers to specify % of traffic between two ip address. So you could have 99% of your traffic to one ip and 1% to the other. When the primary server goes down it will in a matter of seconds swap to the 100% of the traffic to the 1% ip specified.

I used it a few years back but the problem (as with most DNS today) is the complication of having dynamic content on those servers were not updated.

I will look into DNS servers that still support this...
 
joe2bron said:
We want to be able to have one major hosting, and only when this major one is down, then the other one will be available to the visitor.
Any suggestion how to configure ?
Two ways come to mind, one not precisely what you want:

1) Redundancy & automatic failover:

Run DNS and webhosting on two systems. On system one, in DNS set up only master DNS for the domain, with the IP pointing to server one.

On system two, in DNS set up only only master DNS for the domain, with the IP pointing to server two.

List both ns.server1 and ns.server2 as the two nameservers for the domain, with the registrar who registered the domain.

That way, all visitors who get DNS from server1 will see the site on server1 while all visitors who get DNS from server2 will see the site on server2.

You'll need a short TTL, so visitors who, for example, were seeing server1, will see server2 soon after server1 fails.

2) Automatic failover only (more complicated):

Set it up the same way but leave DNS on server two turned off. Write a script for server two that continues to check both DNS and HTTP on server 1, and if it can't get a response from either, turns on the server 2 DNS server.

But this isn't as foolproof as (1), because (a) there could be a problem with the network between the two systems, so server 2 would start resolving even if server 1 was still running, and (b) if server one suffered a network problem that made it invisible to half the net, but server two could still see it, half your potential visitors wouldn't be able to see the site, because server two wouldn't start.

So I prefer (1), though it isn't quite what you asked about.

Jeff
 
Re: Re: Redudncy DNS

jlasman said:
Two ways come to mind, one not precisely what you want:

1) Redundancy & automatic failover:

Run DNS and webhosting on two systems. On system one, in DNS set up only master DNS for the domain, with the IP pointing to server one.

On system two, in DNS set up only only master DNS for the domain, with the IP pointing to server two.

List both ns.server1 and ns.server2 as the two nameservers for the domain, with the registrar who registered the domain.

That way, all visitors who get DNS from server1 will see the site on server1 while all visitors who get DNS from server2 will see the site on server2.

You'll need a short TTL, so visitors who, for example, were seeing server1, will see server2 soon after server1 fails.

The only problem with this solution is it does not work well for users with dynamic sites. If the site uses a database it can make it a bit easier since you can setup a 3rd server to contain all the dynamic content BUT then you now have to figure out a solution for the database server.

The other problem is it does work with DirectAdmin at all. You would need to modify how it creates users.

Its is the same idea of what we do with large customers but they don't need to have the versatility of DA.
 
Re: Re: Re: Redudncy DNS

existenz said:
The only problem with this solution is it does not work well for users with dynamic sites. If the site uses a database it can make it a bit easier since you can setup a 3rd server to contain all the dynamic content BUT then you now have to figure out a solution for the database server.
I didn't address the issue of dynamic content update because you already had. Perhaps I should have.

The best way to address the dynamic site issue, as has been addressed on other forums many times, is with some kind of file redundancy. I prefer some kind of replication system to NFS and a database server because otherwise the database server becomes a point of failure.

There's no such thing as true redundancy with no point of failure; we've studied virtually all the models we've found, including some very expensive ones, and they all have points of failure; some multiple points.
The other problem is it does work with DirectAdmin at all. You would need to modify how it creates users.
Why doesn't it work for you? It works fine for us.

Jeff
 
Re: Re: Re: Re: Redudncy DNS

Why doesn't it work for you? It works fine for us.

Jeff [/B]

Right, right, Dynamic content is easy as long as your not using a control panel or anything like to to maintain the sites. If you do it by hand it is easy.

I honestly might not be thinking the same thing as you but how can one get it to work with DirectAdmin. I could see you using the first solution (and have seen it used before) but how can you get it (I guess it's possible with the API's) to create the sites on both server? I think he would want everything, sites, email and etc to by on both machines. I guess you could use a Tiara?

I am honesly am just wondering no disrespect...
 
No disrepect given, and none taken.

We currently do it ourselves for various services, including one website and both POP and STMP email; we don't use DA on the second server.

If we decide to offer it to clients (we have not made the decision at this point, though some of our clients have asked about it) we'll probably do it with a replication system to copy the files Directadmin maintains/cares about, from one server to the other.

To simplify replication we'd require the user login to only one server for maintenance.

We haven't come up with an answer for imap email; we probably wouldn't support it. POP and SMTP based email is easy enough to manage this way.

As I said, nothing is perfect.

Perhaps we'll just go the easier route; two systems both using the same NFS datastore, as in NAS (network attached storage); after all that's what the most expensive commercial solutions depend on, so it wouldn't be a hard sell.

Jeff
 
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I see where you were going with that. That is probably one way I would have thought about it. I thought you had a idea on how to make DA work between 2 machines. I bet with a little ingenuity one could use existing API's (possibly need some more) to make it work. That would been a neat solution...
 
Sure it can be done...

If I recall correctly either ModernBill or Whois.Cart allows multiple server administration (thought I might be wrong; it might just be in a wishlist).

Jeff
 
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