Date: Tue, 14 Nov 1995 15:27:42 -0500 (EST) From: "Jonathan M. Bresler" <jmb@kryten.Atinc.COM> To: isp@freebsd.org Subject: Re: Multiple http servers - howto ? (fwd) Message-ID: <Pine.3.89.9511141524.R13861-0100000@kryten.atinc.com>
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would one of you write up a procedure for this. i would be the first entry in the isp faq that i have promised to produce.....from your input ;) come on guys.....someone must be doing this. dont need a 100% solution. general success will be a great starting point. jmb Jonathan M. Bresler jmb@kryten.atinc.com | Analysis & Technology, Inc. FreeBSD Postmaster jmb@FreeBSD.Org | 2341 Jeff Davis Hwy play go. | Arlington, VA 22202 ride bike. hack FreeBSD.--ah the good life | 703-418-2800 x346 > > > > #1. Via DNS. The requesting hosts are rotored through a list of the > > > > addresses. > > > > > > > > It isn't a very good scheme, mostly because caching exists. > > > > > > Which is why you lower the TTL :-) or maybe just not worry about it, > > > because when you start examining the Bigger Picture, you realize that a site > > > large enough to require multiple servers is receiving zillions of requests, > > > and different data will be cached by each domain server, still effectively > > > spreading the load over multiple servers. > > > > *My* cache doesn't have to honor *your* TTL. In fact, if my provider > > is Sprint or one of serval others, it *won't* honor your TTL. > > If you are using Sprint for domain service, I pity you. Nevertheless, the > TTL only assists in randomization. > > > You're still doing round-robin address assignment, which expects that > > clients will behave statistically identical to one another. And they > > won't, even if the TTL is honored. > > Somebody else who doesn't really understand that when N is a random function > that may not be random for small values of x, still is random enough for > large values of x.... :-) > > The TTL hack simply reduces the definition of "may not be random for small > values of x". > > If you are trying to tell me that if I have 4 addresses and 5,000 sites do > a DNS lookup on me, I will state that at least 1,000 sites will get assigned > to each address. That does not imply that the loading will be identical or > totally equal, but it should be reasonably distributed. I may not care if > the distribution is 1000/1000/1000/2000, because it is still better than > 5000 against a single box - and I would bet that it would be more evenly > distributed than I am suggesting, most of the time. > > For smaller cases, you don't care because you don't need multiple server > platforms to begin with. > > > > The case where you might lose is if a hundred workstations at the same site > > > suddenly decide to all run Netscape on a particular URL at once, all hundred > > > workstations receive the same cached answer from the local domain server, > > > and they proceed to pound the box into oblivion. This is the "University > > > Intro to CS class" problem. It's worse if they are pounding on your news > > > server :-( which HAS happened to me. > > > > Or one of several server boxes with 40 X terminals hanging off it. > > Both of which are cases where the sample size "x" isn't large enough (well, > of course, in the case of the news server, there was only one news server). Jonathan M. Bresler jmb@kryten.atinc.com | Analysis & Technology, Inc. FreeBSD Postmaster jmb@FreeBSD.Org | 2341 Jeff Davis Hwy play go. | Arlington, VA 22202 ride bike. hack FreeBSD.--ah the good life | 703-418-2800 x346
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