[isapros] Re: Array Member Failover

  • From: "Jason Jones" <Jason.Jones@xxxxxxxxxxxxxxxxx>
  • To: <isapros@xxxxxxxxxxxxx>
  • Date: Fri, 26 May 2006 21:19:17 +0100

Thanks for the reply Jim -  I don't want to disagree, as I repsect your
input and knowledge, but I thought the autoconfig script was designed to
include an element of failvoer in addition to load balacing? Are we
saying that this failvoer is just too basic to actually rely upon?

When I say autoconfig, I mean client-side CARP and based upon ISA help:

ISA Server supports the Cache Array Routing Protocol (CARP). CARP
enhances Web performance by providing both load balancing and
transparent failover for Web proxy browser connections.

As I said, I would love to use NLB, but client limitations with NIC
teaming won't let me! Am I really expecting too much from the auto
config script in the event of server failure?

Cheers

JJ

-----Original Message-----
From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Jim Harrison
Sent: 26 May 2006 20:49
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: Array Member Failover

WPAD is not designed to provide failover/back.
As you've noticed, this is not going to work.
WPAD is nothing more or less than a "load-spreading" mechanism that
allows the client to use a different ISA for different destinations.

If you want failover/back, use NLB or another traffic-management system.

-----Original Message-----
From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Jason Jones
Sent: Friday, May 26, 2006 12:42 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: Array Member Failover

Cheers Tom - unfortunately closing the browser doesn't seem to fix the
problem...IE still trys to connect to the primary autoconfig defined
server first then eventually use the other array members (after about
20-30 seconds). This behaviour seems to happen repeatedly on all clients
fdor every new URL entered 
 
The only way to fix it is to bring the failed server back online :-(

________________________________

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Thomas W Shinder
Sent: 26 May 2006 12:18
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: Array Member Failover


Hi Jason,
 
Not too low brow for me :)  This is a common question with a common
non-answer in the public realm. 
 
What you need to do is close all browser windows and open a new one.
Then the client connects to a live server. I've never worked out in
detail why this happens, but it's related to the autoconfig script
processing [hand waving explanation]
 
Maybe somebody else can chime in with a more detailed explanation.
Bottom line is that you're not going to get completely transparent
failover for Web proxy clients.
 
Tom
Thomas W Shinder, M.D.
Site: www.isaserver.org <http://www.isaserver.org/>
Blog: http://blogs.isaserver.org/shinder/
Book: http://tinyurl.com/3xqb7 <http://tinyurl.com/3xqb7> MVP -- ISA
Firewalls

 


________________________________

        From: isapros-bounce@xxxxxxxxxxxxx
[mailto:isapros-bounce@xxxxxxxxxxxxx] On Behalf Of Jason Jones
        Sent: Thursday, May 25, 2006 4:44 PM
        To: isapros@xxxxxxxxxxxxx
        Subject: [isapros] Array Member Failover
        
        

        Hope this question is not too low brow, if so, kick me and I
will move it to isaserver.org for the masses to mull over ;-)

        Anyhow, has anything changed with array member failover behavior
in EE with ISA2k4 SP2? I am sure I have never had problems with array
member failovers in the past...

        I have recently deployed an SP2 array with several members and
while testing I have noticed that if the server listed as the first
entry defined within the wpad.dat file is unavailable then the browser
delays for quite some time before attempting to connect to other array
members (e.g. working through the server list in the wpad.dat file). It
does seem to get there, but we're talking 20 seconds or so per website.
Once the website is loaded, performance is fine. When using a new URL,
the delays appears again.

        Apart from failover, balancing and distr caching seems to be
working well. I know I could be using NLB, but I believe the following
to be good practice:

        Web Proxy => Autoconfig script (client side CARP) 
        FW Client => RR DNS 

        I am using a generic name of customerarray.domain.com with RR
DNS entries to balance autoconfig requests between array members. This
is the name used in the autoconfig URL.

        I know NLB may come to mind as a workaround, but it is hard to
implement as the customer is using NIC teaming at the hardware driver
level to aggregate NICS and provide NIC fault tolerance. NLB and NIC
teaming never play well from what I have experienced :-(

        Can someone please define normal behavior for a client that is
using an autoconfig script when array members are unavailable? I kinda
get the feeling the problem is with the browser and not the array, but
not totally sure when IE does with the script in terms of processing...

        I've tried looking at wpad.dat caching and caching of bad
proxies, but neither seems to make much difference... 

        Any ideas? 

        JJ 


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