Rails - Jun 2006 - fcgi_watch (reaper replacement for shared servers)

fcgi_watch is a supplement to (or replacement for) 
<rails_app>/script/process/reaper.

The standard reaper script searches for all processes started with a 
given pathname using the output from a ps command, and performs an 
action on them. There are problems with this approach, at least on some 
shared servers:

 - The pathname seen from a script is not necessarily the same as the 
pathname seen from a shell command. You can determine whether you have 
this problem by typing a pwd command, then ruby -e ''puts
`pwd`''. If the
results are different, the problem exists.

 - At least on some servers, if you have two or more Rails applications 
running, all of the FCGI dispatchers will look the same to the ps 
command. This means that any action performed by reaper will affect all 
your Rails applications.

HOW DOES fcgi_watch SOLVE THESE PROBLEMS?

fcgi_watch finds and parses the fastcgi.crash.log in the <rails_app>/log 
directory. It makes a list of processes that should be running, then 
cross-checks it against the output of ps to find all the FCGI processes 
that are actually running for a specified application. Only then does it 
perform the specified action.

BUT THAT''S NOT ALL!

Managing FastCGI processes on a shared server is sometimes 
problematical. You have little control over the web server used, over 
its configuration, or over the activities of other users. Your 
dispatchers might get swapped out and become "unresponsive", causing
the
server to start new ones. After a day or so, "ps aux" might show eight
or ten copies of dispatch.fcgi -- more, if you have multiple 
applications -- and you have no way of knowing which ones of them can be 
safely killed.

fcgi_watch provides an "expire" action, in addition to the actions 
provided by reaper. fcgi_watch keeps track of the ages of instances of 
dispatch.fcgi, and can "expire" processes older than a given number of
hours. You can also set a maximum number of FCGI dispatchers that you 
want to allow for a given application. "fcgi_watch expire" will 
terminate the extras -- gracefully, if possible.

You can get fcgi_watch here:

http://www.alevans.com/dl/fcgi_watch-0.3.0.tgz

I wrote fcgi_watch to solve my FCGI management problems, and it''s made 
my life easier. Hope it helps someone else out!:-)

Please email me with any problems, suggestions, improvements, etc.

--Al Evans


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