Fault Tolerant web service- how & why

Fault Tolerant web service- how & why

Post by Kevin Kad » Sat, 11 May 1996 04:00:00

>I can't figure out how to create fault tolerance on a
>web server.

>All I want is when my web server goes down, a backup
>one will kick in - kind of like the way you can do
>it with e-mail.

It can be done, but it's not as easy as it should be. DNS supports the ability
to have a single machine name with multiple address records. Many telnet and
FTP clients handle these correctly- they get the DNS lookup, try the first
address, and if it fails, try the next one, until one succeeds or they run
out of addresses.

I've mentioned this since '94, but so far NONE of the popular browsers handles
this correctly- if the first server on the list fails to respond, they report
an error, rather than trying the alternate addresses.

Thus, you must implement the fault tolerance on your site. There are several
possible ways to do this, all involve having multiple machines which can
take on the IP address of www.yourdomain.com when the primary server fails.

Since most failure modes will leave the box 'up' (responding at it's IP address)
but not responding to HTTP requests, setting up failover can be rather
complicated. A solution might require a PIX address translation box or a
router/bridge/hub where ports can be selectively turned off.

Because of DNS caching, you can't just change the address the name points to
when the first server goes down, you must actually take the old web server
host off your LAN (free up the IP address) then have a different host assume
it's IP address. Tricky stuff.


Fault Tolerant web service- how & why

Post by Unicom d.o. » Thu, 16 May 1996 04:00:00

Did you ever think about VMScluster?


Fault Tolerant web service- how & why

Post by Khan Mark Klat » Fri, 17 May 1996 04:00:00


> Did you ever think about VMScluster?

I try not to, thanks.