On 7/1/2010 1:46 AM, jean-frederic clere wrote:
On 07/01/2010 03:14 AM, Daniel Ruggeri wrote:
On 6/30/2010 7:34 AM, jean-frederic clere wrote:
On 06/30/2010 04:17 AM, William A. Rowe Jr. wrote:
Yet again, in class another student pointed out that the
Enabled/Disabled
choice in mod_proxy_balancer totally ignores the concept of quiescing,
where we are taking a server offline, but continuing to serve those
requests targeted by session to that server. Once the number of
sessions
settles on something quite low, the user then takes that server offline
entirely and the remaining users are subjected to 'expired session'
results.
A boolean Enabled/Disabled flag doesn't address this need.
Does anyone feel like working on this feature, since those I had
previously approached didn't have all that much interest, or got
busy with other things?
There are several things that requires improvements:
1 - The default load balancing logic doesn't work well when you restart
a back-end node.
...
Cheers
Jean-Frederic
Jean-Frederic;
Can you elaborate more on point 1? I have had issues where a back end
application was not ready during a restart and throws a 503 to Apache.
Since this is a perfectly valid response to the proxied request, Apache
happily sends it along to the user. I wrote a bug (48939) and submitted
a patch that creates a configuration directive to help mitigate this
issue which is the most significant issue I have come across during a
simple back end restart. The patch is currently proposed in STATUS, but
has not received votes to go forward (or stay in STATUS).
That is something different the algorithm used doesn't work correctly
when you have long lasting sessions and the load for the past is not
forgotten... Basically to much load is going to the returning back-end.
Your patch is just a work-around to the problem that httpd doesn't know
that the back-end shouldn't be used at that time.
Cheers
Jean-Frederic
Jean-Frederic;
That's a very good point and a qualm I have had with httpd for a
while myself. As it is, the current balancer setup relies on live
traffic to figure out if the backend is OK. Some hardware load balancers
have the ability to "ping" backends with anything from simple TCP, HTTP
HEAD or even SSL handshakes. Perhaps adding something like that to HTTPD
would be the trick? The logistics of configuring such a thing might be a
little complicated in httpd.conf... perhaps another argument that can be
passed to ProxyPass?
Configured like so?
ProxyPass (or ProxySet or BalancerMember) /context
http://someBackend:1234/context httpProbe="HEAD /context/helloWorld.do"
probeInterval=15
Of course, this is all conceptual - what do you think of the idea? While
this is a feature that would be *incredibly* useful, I don't think I
have the required expertise with httpd's code to execute it.
--
Daniel Ruggeri
