On Fri, 21 Mar 2003, Gordon Messmer wrote:
Jon Nelson wrote:
DNS round-robin has /so/ many problems -- you have to set the ttl incredibly low for it to work at all
That's not correct. "ping mail-test.real.com" ten times and you should get about half of the lookups to one box, and half to the other.
The problems I'm talking about involve /caching/ of the response. The typical ttl on a response is usually 24 hours. Even /if/ your network is set up such that clients ask the server directly when resolving, /and/ the clients *don't* do any caching, you *still* get roughly 50% of the answers wrong. By "wrong" I mean I'll get an IP for a server that isn't up.
That's true, and we'll end up handling this with either LVS (like you suggested) or with Linux-HA's failoverd. Probably the latter, since we'd have to use it anyway to build an HA LVS gateway, and it won't require an additional set of machines.
The LVR/NAT and LVS/DR solutions are much "better" from a high level perspective. Heck, you could probably get away with a Pentium 200 level machine as the NAT/DR "router" - it just passes and mangles packets.
What sense does it make to spend 15K on a cluster of boxes and then skimp on the HA gateways?
Who says you are skimping? If you need a certain amount of horsepower to perform a job, why bother with grossly exceeding that limit?
Your primary concern when building an LVS gateway shouldn't be horsepower (except to make sure that you don't run under), but reliability. I wouldn't use "a pentium 200" because:
* pentium 200's are big. We're mostly using RLX blades here because the network is CRAMPED.
Blades are tiny:
http://www.rlx.com/
http://www.rlx.com/products/chassis/300ex.php
* pentium 200's are old, and I wouldn't really trust the hardware to be reliable
* a single box can fail, LVS gateways need to be clustered, themselves, to be of use in an HA setup.
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