On 04 May 2006, Ken Dombeck said:
> We have 2 applications installed inside the same Tomcat 5.0 instance
> app1 and app2. URL app1.url.com is for app1 and app2.url.com is for
> app2. Both URLs have the same ip address but still hit port 80. The
> maxThreads for the connector is set to 100.
>
> The problem we are experiencing is that app2 will slow down and consume
> all 100 of the connector threads. What we would like to do is limit the
> number of threads that each application can use to 50 so that one
> application can not cause a denial of service attack to the other
> applications in the container. By limiting the number of connections to
> 50 we would expect the 51st connection to that application to wait until
> a thread freed up.
Wow, I asked this very same question just the other day.
Tim Funk <funkman at joedog dot org> kindly provided the following
suggestion:
> An "easier solution" is to throttle the webapp via a filter. For example:
>
> Filter{
> final int maxThreadCount=10;
> int threadCount=0;
> doFilter() {
> synchronized(this) {
> if (threadCount>maxThreadCount) {
> response.sendError(SC_SERVICE_UNAVAILABLE);
> return;
> }
> threadCount++;
> }
> try {
> chain.doFilter(request, response);
> } finally {
> synchronized(this) {
> threadCount--;
> }
> }
> }
> }
I have implemented something like this for us and it works like a
charm. Haven't got it into production yet though.
Oh yeah, Tim's pseudo-code has an off-by-one error in it: I ended up
using the equivalent of
doFilter() {
synchronized(this) {
if (threadCount >= maxThreadCount) {
response.sendError(SC_SERVICE_UNAVAILABLE);
...
And if your problem is at the level of whole webapps, make sure you
apply the filter to whole webapps. Here's a snippet from my web.xml
that configures this filter:
<!--
Filter to throttle the number of concurrent requests across the
whole webapp.
-->
<filter>
<filter-name>throttle</filter-name>
<filter-class>com.intelerad.web.lib.RequestThrottler</filter-class>
<init-param>
<param-name>max_concurrent_requests</param-name>
<param-value>5</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>throttle</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
The <filter-mapping> is the important part to make sure it covers a
whole webapp.
Greg
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