Date: Fri, 26 Apr 2002 08:36:08 +1000 (EST) From: Colin Campbell <sgcccdc@citec.qld.gov.au> To: Emre Bastuz <info@emre.de> Cc: <freebsd-isp@FreeBSD.ORG> Subject: Re: HTTP Load Balancing and Availability Solutions Message-ID: <Pine.BSF.4.33.0204260816040.20847-100000@guru.citec.qld.gov.au> In-Reply-To: <3CC6A5D2.3070701@emre.de>
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Hi,
On Wed, 24 Apr 2002, Emre Bastuz wrote:
> Hi,
>
> I=B4m looking for a software that does the job of accepting
> HTTP request as a webserver and then distributes these
> to other servers - depending on which one is currently up.
Here's one way. The "real" IP address of each web server is configured as
a loopback alias on every host. Use dynamic routing (eg OSPF) to allow the
router to deicde which host to send the packets to. When a host dires, it
might take 10-15s for the routes to change but it all happens
automatically. Example:
2 x host
4 x httpd each with own IP
On both hosts, create 4 IP aliases on loopback,
=09ifconfig lo www.a.com alias
=09ifconfig lo www.b.com alias
=09ifconfig lo www.c.com alias
=09ifconfig lo www.d.com alias
Let's say that under normal circumstances we want host-1 to serve www.a
and www.b and host-2 to serve the other two.
On the router configure the dynamic routing as follows:
=09destination www.a.com via host-1 cost 1
=09destination www.b.com via host-1 cost 1
=09destination www.c.com via host-1 cost 2
=09destination www.d.com via host-1 cost 2
destination www.a.com via host-2 cost 2
destination www.b.com via host-2 cost 2
destination www.c.com via host-2 cost 1
destination www.d.com via host-2 cost 1
By default the router will send all traffic to www. and ww.b to host-1 and
the other two servers to host-2. If host-1 goes down, the link-state
information (eg in OSPF) will tell the router to go via host-2 to www.a
and www.b since the link via host-1 is no longer available.
This way you don't need a lot of extra hardware (the web servers might
need to be a bit bigger than normal), it's scalable, provides some
(manual) load balancing and can fail over automatically and very quickly.
Colin
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