Well, you can use round-robin DNS which means that for the hostname you'll assign two IP addresses. You just assign multiple A records for the hostname.
Sometimes the answer is so simple you just don't see it! Would this *just* provide fault tolerance (if one card goes down, it gives the next IP)? i.e. not load balance. Or does it alternate which IP it gives out to the client issuing the request?
TIA Ricardo
(PS Martyn- my RH system is now bang up-to-date- no probs whatsoever with the kernel upgrades!)
On Thu, 14 Feb 2002, Ricardo Campos wrote:
Well, you can use round-robin DNS which means that for the hostname you'll assign two IP addresses. You just assign multiple A records for the hostname.
Sometimes the answer is so simple you just don't see it! Would this *just* provide fault tolerance (if one card goes down, it gives the next IP)? i.e. not load balance. Or does it alternate which IP it gives out to the client issuing the request?
All that happens is the DNS server gives one address and then the next, it alternates between the two so you don't really get any fault tolerance if one of the cards goes bang but at least 50% of request for service would get through so it's better than nothing.
The only way I can think of getting real fault tolerance would be some kind of either hardware or software load balancing, which is not cheap.
Although there is another possibility, whereby you write a script that runs on the server and watches both ethernet interfaces, when one stops working you nick its ip address and alias it to the other ethernet card.
Adam
On Thu, 14 Feb 2002 13:51:36 Adam Bower wrote:
Although there is another possibility, whereby you write a script that runs on the server and watches both ethernet interfaces, when one stops working you nick its ip address and alias it to the other ethernet card.
The other component that I had heard of in connection to this was that when the daemon switches over the network interface, it has the working interface send out (unsolicited) ARP replies to tell routers etc of the new ethernet address associated with the IP.
Steve.
Sometimes the answer is so simple you just don't see it! Would this *just* provide fault tolerance (if one card goes down, it gives the next IP)? i.e. not load balance. Or does it alternate which IP it gives out to the client issuing the request?
Round-robin DNS will hand out the two IP addresses alternatively.
It is not proper load balancing, since it assumes that both NICs are equally charged which might not always be the case. Proper load balancing is hard to do.
It is not fault tolerant: if one of the NICs goes down, the DNS server will still hand out that NIC's IP address to clients half of the time, until it gets reconfigured. A script can run in the background, periodically check if the NICs are still alive and reconfigure the DNS server when necessary.
Cheers,
Eric.
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Adam Bower -
Eric Sellin -
Ricardo Campos -
Steve Fosdick