[Building Sakai] Httpd 2.2 MaxClient Problem

[Jeff Cousineau]

At Michigan we're currently running the following configuration in production (apache httpd 2.2.x, tomcat 7.0.x):

MinSpareServers 20
MaxSpareServers 50
StartServers 20
ServerLimit 2048
MaxClients 2048
MaxRequestsPerChild 10000

We recently bumped up ServerLimit & MaxClients from 1024 as we've seen a significant increase in simultaneous connection counts over the past year or so.  We're now routinely in the 700-900 simultaneous connections range (active connections to port 443 per app server) during our daily highest usage periods in the Fall & Winter academic terms.  This connection "load" is consistent across all 11 active application servers.  We proactively increased the threshold to minimize the possibility of hitting those resource limits during additional load spikes.  

We also increased maxThreads in tomcat to 1024 per app instance.  We were more conservative in that increase (up from 768 previously) because we're already running a large JVM configuration (12GB heap).  Also, we offload serving of static files to apache rather than passing request through to tomcat to serve so we've configured apache httpd to accommodate those requests.

We haven't done much tuning of the other apache directives noted above in quite some time.  There may be some historical reason why they're set the way the are but it might require an archeological expedition to attempt to rediscover the rationale.  :-)  Those settings haven't changed since at least 2008 (probably when we upgraded from apache 1.3.x to apache 2.x)…

Jeff

On May 16, 2013, at 7:28 AM, Adrian Fish <adrian.r.fish at gmail.com> wrote:

> Ours is set to this. The default, as you can see, was set to 150.
> 
> <IfModule mpm_worker_module>
>     StartServers          2
>     MinSpareThreads      25
>     MaxSpareThreads      75
>     ThreadLimit          64
>     ThreadsPerChild      25
>     #MaxClients          150
>     MaxClients          400
>     MaxRequestsPerChild   0
> </IfModule>
> 
> 
> On 16 May 2013 12:26, Adrian Fish <adrian.r.fish at gmail.com> wrote:
> You need to set maxThreads in your tomcat server.xml as well. It needs to be the same as MaxClients in apache2.conf.
> 
> Cheers,
> Adrian.
> 
> 
> On 16 May 2013 11:52, Jehan Badshah <jehan.badshah at nu.edu.pk> wrote:
> Dear All
> 
> 
> We are using Httpd2.2 with AJP connecter.
> 
> When concurrent users are increasing (i.g., more than 300) then some time Apache (Httpd server) throws following  error
> 
> "[error] server reached MaxClients setting, consider raising the MaxClients setting"
> 
> But in httpd.conf we did not specify any entry like MaxClient, MaxServer 
> 
> I google it and found that we should add following lines to our httpd.conf
> 
> <IfModule mpm_prefork_module>
>     StartServers          A
>     MinSpareServers       B
>     MaxSpareServers      C
>     MaxClients          D
>     MaxRequestsPerChild   E
>     ServerLimit   F
> </IfModule>
> 
> If I did not specify any of above lines then what is default number of concurrent connection and ServerLimit
> 
> At most 500 users come online, so what are best configuration values (i.g., A, B, C, D, E, F)
> 
> 
> 
> 
> Regards
> 
> 
> 
> 
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--

Jeff Cousineau
Application Systems Administrator Senior
Information and Technology Services
University of Michigan

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