Christopher Schultz wrote:
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André,
On 12/7/12 4:16 AM, André Warnier wrote:
Williams, Nick wrote:
-----Original Message----- From: Christopher Schultz
[mailto:ch...@christopherschultz.net] Sent: Thursday, December
06, 2012 5:08 PM To: Tomcat Users List Subject: Re: Is it
possible to expire jvmRoute cookie
2. How one additional user can be a problem in such a system?
If he accesses a heavy-loaded system the things will be slow
for him, but faster for all others, who close their browsers
regularly.
Let's take a pathological example:
Assumptions: 1. Cluster has 3 nodes (A, B, C) 2. Users never
close their browsers
Let's say that server A is rock-solid and never goes down.
Servers B and C are running Gentoo Linux or Debian Sid or
Microsoft Windows or have flaky hardware and so they crash or
need to be rebooted all the time; perhaps daily.
Users on nodes B and C will constantly fail-over to node A.
Those users will stick on node A pretty much forever.
Therefore node A always gets most of the traffic, and nodes B
and C only get "new" users for a while before failing-over.
Even if nodes B and C can handle 1/3 of the load, they will get
much less than that, and node A will, over time, accumulate
users without bound.
It would be nice to avoid this kind of situation.
So one could recommend that if things go slow to close one's
browser, clean caches, or even reboot. ;)
"If I called tech support for a website and they told me I needed
to close my browser or reboot my computer to just to use their
website, I would assume that they were complete idiots. If I want
to be lied to about what the problem is, I'll call my home
broadband provider." <-- HAHAHA ... nice one.
I agree with Chris, here. It's not a "common" situation, but it
is a possible situation, and if it occurred, it could get ugly
quickly.
Earlier somebody (I'm sorry, I already deleted the email)
suggested Tomcat returning a 308 or 309 or similar to the load
balancer to trigger a "re-balance" if the session is expired. I
think this is the best idea I've heard yet, solves the problem
elegantly and simply, and seems (relatively) easy to achieve
(this coming from someone who has no knowledge of the code used
by mod_jk/isapi_redirector).
I must admit that this sounds more elegant (and efficient) than my
suggested interceptor module.
Alternatively, if one wanted to avoid touching mod_jk for this,
maybe tomcat could return a 302 redirect to the starting page of
this application, if known ? (without jsessionid.jvmroute of
course).
That's definitely an idea worth pursuing: an expired session id could
return 302 *and* strip the jsessionid path parameter *and* send a
Set-Cookie JSESSIONID; expiration=0 header (which deletes the cookie).
The client would re-try and the balancer would re-balance.
Konstantin, what do you think? Obviously, this shouldn't be the
default operation of Tomcat, but perhaps a setting that could be
enabled on the session manager?
By the way, that should work with mod_proxy_ajp too, which I suppose has a
similar behaviour.
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