Date: Sat, 7 Apr 2001 18:19:30 -0700 (PDT) From: <lamont@scriptkiddie.org> To: Matt Dillon <dillon@earth.backplane.com> Cc: Benjamin Flom <benf@nexgen.com>, <freebsd-stable@FreeBSD.ORG> Subject: Re: Cluster Solution for FreeBSD Message-ID: <Pine.LNX.4.30.0104071807530.9512-100000@coredump.scriptkiddie.org> In-Reply-To: <200104062317.f36NHJW48955@earth.backplane.com>
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On Fri, 6 Apr 2001, Matt Dillon wrote: > The quick and dirty thing to do is simply setup a DNS round robin > for the domain name used to access the servers. For example, if > you are serving a web site called www.flubber.com you would > setup the DNS for www.flubber.com to return several IP addresses > (multiple IN A records) instead of just one. There isn't much point > having several servers available if all the traffic is only going to > one of them, and the random distribution the round robin gives you > is usually sufficient to distribute the load enough that you don't > really need sophisticated load balancing software. > > That leaves just dealing with downed servers. There are several > solutions, but what it comes down to is that no matter what you do > something is going to glitch when a server goes down and the real > question is "how long" before that glitch clears. My take on the > situation is that since there is no way to avoid the glitch (even with > something like a Cisco redirector), using a DNS-based solution and > short record timeouts is the least intrusive. The site might glitch > for a few minutes when something goes down, but it will still correct > itself quickly enough that in the day-to-day running of most businesses > (e.g. anything except a brokerage site, say), nobody is going to care. > It depends on what you are doing, of course. Some sites require much > more stringent controls. you can also use LSNAT on a Cisco router to give this kind of lightweight load balancing, while not having to worry about DNS caches on machines that you don't control (and if all your machines are already sitting behind a 26xx router or something, you pay $0). of course the downside to this is that you have to worry about persistance across webservers in your application. and i'd argue pretty strenuously with you about only brokerage sites needing to have better availability than what you get with round robin DNS. you can buy a decent webserver load balacing configuration for $20k and this can easily save you from several hours of downtime a year. if you've got a $10M/year site this will probably pay for itself in the first year. > Run the numbers and determine if you care. e.g. say you have 3 servers > and a server crashes on average once every 60 days, glitching the > network for 10 minutes. i'm also a little skeptical that a typical round-robin DNS recovery time would be 10 minutes. maybe if you roll your own scripts and have them automatically take failed machines out of DNS... those scripts will need some debugging time though and you can probably expect one or two much longer downtimes as you work the bugs out... of course i completely agree that you need to weigh the alternatives and evaluate what your unique requirements are. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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