[f-nsp] Re: can this be done?

[Clifton Royston]

On Wed, Jan 22, 2003 at 01:13:53PM -0600, Kim Wall wrote:
>    "I think I could achieve 2, 3, and 4 by defining the servers as
>    "remote" instead of "real" and configuring DSR, but the documentation
>    seems to imply that the ServerIrons can't automatically detect a
>    failed server in that case."
>    
>    Clifton, not sure what version of software you are using, but I know
>    that the SI-XL still performs "pings" as a basic health check to
>    remote real servers using version 7.3.05. This is done automatically.

  This was a good tip, and got me thinking (and reading the docs deeper)
about how to enable additional health checks.

  For those Googling the mailing list, it turns out to be perfectly
easy to configure further application layer checks in conjunction with
a "dsr" or "Switchback" configuration.  Setting up explicit health
checks on http to work with DSR or Switchback, e.g. in an
asymmetrically routed network, is as simple as this:

server port 80
 ! number of seconds and retries between polls
 tcp keepalive 60 2  

server real foo xx.yy.zz.ww
 port http
 port http keepalive
 port http url "HEAD /"

server real bar xx.yy.zz.vv
 port http
 port http keepalive
 port http url "HEAD /"

server virtual baz xx.yy.zz.qq
 port http dsr
 bind http foo http bar http

  If you tail the http logs on the real servers, you will see the
"HEAD" requests from the ServerIron itself show up every 60 seconds, or
however often you've configured them, along with whatever connections
get made to the virtual server.

  This also appears to work in the multiple subnet and multiple VLAN
environment I was originally concerned about.

  -- Clifton

-- 
     Clifton Royston  --  LavaNet Systems Architect --  cliftonr at lava.net

  "If you ride fast enough, the Specialist can't catch you."
  "What's the Specialist?" Samantha says. 
  "The Specialist wears a hat," says the babysitter. "The hat makes noises."
  She doesn't say anything else.  
                      Kelly Link, _The Specialist's Hat_