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For outside browsers, they're hitting the Squid server, which then
Re: How does loadbalancing work?
From: Men & Mice Support
Date: Thursday, May 24, 2001
Time: 11:52:53 pm
hits the correct (up & running) web server. So outside users aren't
then affected by this problem of browser memory. It will then only
affect your internal hosts.
There's a flip side, though - you can't guarantee that an end-user
will continue to hit the same server throughout their visit. So if
you have any sort of interactive stuff that needs to track a given
visitor (WebObjects, Interaction, HTML/OS, etc.), it's going to
occasionally break as a visitor is diverted to the development
server, and then back again a few minutes later.
In fact, since it's the Squid server that's getting switched, *all*
traffic from the outside will hit the main server, except for
occasional stretches (length determined by your TTL, frequency by
your load balance settings) where they'll *all* hit the dev server.
____________________________________________________________________
Chris Buxton Men & Mice
cbuxton@menandmice.com We Make DNS Easy!
At 5:29 PM +1200 5/25/01, Jono wrote:
>Found something interesting...
>
> > A browser will actually cache that answer until it is quit and
> > relaunched. The DNS resolver will cache the address of one of the web
> > servers for 300 seconds (5 minutes), because that's the TTL of your
> > load balance record.
>
>(http://archive.digitalpoint.com/FMPro?-db=listarch.fp5&-lay=web&-RecID=1260
>2067&-Format=/QDNS/archdetail.html&-Find)
>
>OK, we have an intranet application that we've been chasing down some
>serious (and painfully elusive) stability problems with the main web server.
>
>We _know_ how to crash our development server with huge/complex SQL queries,
>which is why we have a development server :) But, apart from those
>overloads, the dev server is rather stable (to date).
>
>So, I set about load balancing the main server 99/1 with the dev server
>(mirrored hostname.domain, not the dev.domain). Low TTL and interval values.
>
>Worked great if when the main server was down, quit IE (mac) and relaunch,
>it would switch over to the dev server... but no 'on-the-fly' switch. came
>to the same conclusion as above, the IE was not releasing Open Transport to
>expire it's TTL appropriately.
>
>But we run all external browsing traffic through one OSX box running Squid
>(proxy, fast, cool, _free_), and I had this stupid idea that Squid might
>honour the TTL records. It does!
>
>Now, with proxy not excluding that domain, if the main server goes down,
>there's a few second's pause, then squid hits up the dev server for the
>data. When the main server comes back online, squid seems to switch back to
>it in just a few short seconds... same browser session.
>
>Makes me think it's a Mac problem - or does the behaviour described in the
>above quoted happen with PC's as well?
>
>I know this has limited use in the 'real world' but it was certainly a
>revelation.
>
>Thank God the server has been going down less as we have eliminated issue
>after issue.
>
>Jono
>
>___________________________________________________
>Jonathan Guthrie
>New Media Solutions Designer
>
>DNA Design
>Wellington NZ
>
>jono@dna.co.nz
>___________________________________________________
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