Hi Gerhardus,
On 30.12.2008 17:53, gerhardus.geldenh...@gta-travel.com wrote:
Hi
We have an apache server that load balances two types of applications
across different stacks of tomcats.
We have a tomcat stack for requests that processes very quickly, lets
call this stack A and a tomcat stack for slower running
request(different type of application) named stack B.
We limit connections on the apache to protect the underlying layers eg:
ServerLimit 5
ThreadLimit 10
StartServers 5
ThreadsPerChild 10
MinSpareThreads 10
MaxClients 50
MaxSpareThreads 50
However if stack A or B misbehave and eat up all of the available apache
connections it can cause a denial of service for the other stack that is
on the same apache.
My question really is where I should be doing the isolation. I am not
sure whether I can achieve this in modjk or whether I should rather be
running separate apache instances for tomcat stack A and B. I considered
using virtual hosts but I believe they would still share the overall
amount of threads as defined above.
Yes, they will. So if you want best separation, yes you would use two
apache instances.
Of course you could try to find a middle way between absolute separation
and consolidation, the latter allowing to use resources of stack A for
stack B (or vice versa) up to a certain amount.
You can't map httpd threads to URLs, and since the mod_jk connection
pools are process local, you can't really efficiently divide the
connections (=threads) available for requests to A and available for
requests to B.
What's possible though is using reply_timeouts. Most of the time
"misbehave" is getting slow or stuck.
Since
concurrency = throughput * response_time
you can at least partially prepare for eating up all available
concurrency by limiting response times. Unfortunately your maximal
concurrency of 50 is not very big, so one of the two stacks could
quickly eat all available threads.
Until version 1.2.26 of mod_jk you had to use two separate workers for A
and B in order to set reply timeouts to different values, starting with
the recent 1.2.27 you can use reply timeouts per mount using mount
extensions.
After writing this I think the question is probably more relevant on an
apache list but because we are using modjk and tomcat I thought I would
ask anyway.
Regards,
Rainer
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