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From Rainer Jung <>
Subject Re: mod_jk monitoring
Date Fri, 07 Nov 2014 23:12:26 GMT
Am 07.11.2014 um 23:58 schrieb Christopher Schultz:

> Great. We've been having some problems draining Tomcat nodes, and I
> was concerned that maybe I had overlooked this one possibility. Our
> next release will include a version of the recently-discussed
> load-balancer draining filter/valve so we'll see how that does.

There are some tricks also in mod_jk to improve draining:

- people using an old session id without an existing session, e.g. 
having a JSESSIONID cookie or who bookmarked a jsessionid-encoded URL, 
will hinder draining. Typically clearing the cookie during logout 
doesn't happen. So what you can do is twi things:

- you can use mod_headers to force cookie clearing on a logout URI by 
setting the Set-Cookie header to an empty JSESSIONID cookie if the URI 
matches your logout URI

- you can use mod_setenvif or mod_rewrite to set the Apache environment 
variable JK_STICKY_IGNORE to "1" for requests that might have a session 
id but can actually be handled non-sticky. E.g. a request for a login 
form from a user that might use an old cookie. If mod_jk sees 
JK_STICKY_IGNORE it will not handle the request sticky, so if you 
already disabled some worker, the request will not be send there, even 
if the cookie points to that worker.

Finally you can use the Tomcat Manager webapp "Expire Sessions" feature. 
If you click it, it will not really expire sessions (actually only those 
that the automatic expiration would expire during the next run), but it 
will show a histogram of session idleness. Depending on the data you 
might be able to decide, when enough draining happened, e.g. the 
remaining sessions all or nearly all have a long idleness time (but of 
course shorter than the session timeout).



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