Let's start with an example that has nothing to do with god... When you
stop a service, such as crond, its pid file is also removed:
$ cat /var/run/crond.pid
32484
$ service crond status
crond (pid 32484) is running...
$ service crond stop
Stopping crond: [ OK ]
$ cat /var/run/crond.pid
cat: /var/run/crond.pid: No such file or directory
Now in contrast, god does not do this for your watches. *Furthermore, it
doesn't cleanup /var/run/god.pid when you cleanly end it, either.*
There are a few important benefits to cleaning up a PID file when a planned
stop/restart occurs:
1. process IDs are in a finite space and are recycled after ending.
Just because process ID "123" exists both in the process table and in a
stale PID file doesn't mean that our original service is still running. In
other words, checking for your process via `ps -p $(cat
/var/run/my-service.pid)` is _weak_ guarantee that the process you expected
is still running, unless it remains constantly in a monitored state by god.
2. The current behavior relies heavily on the idea that you won't
restart god or unmonitor watches. If you do, god's re-init is forced to
rely on the _weak_ guarantee above to assure itself that watches were not
killed while it was away.
3. If we can correlate the absence of a PID file with a planned
down/stop, then it makes requests like
#156<https://github.com/mojombo/god/issues/156>easy.
w.behavior(:clean_pid_file) is similar to this, but it cleans up during
start-up. We need a behavior for stop. Unfortunately, :clean_pid_file is
such a generic name, that adding another one will certainly lead to
confusion.
Personally, I can't think of a case where you _wouldn't_ want to clean up
the PID file upon a planned "stop" action. That's why I advocate that PID
file cleanup on stop should be an inherent behavior, and not an option.
But I open this up to the group... do you agree that this stop-pid-cleanup
should be 1.) available and 2.) an inherent behavior for all watches that
have a w.pid_file property? Thanks for your thoughts!
--
You received this message because you are subscribed to the Google Groups
"god.rb" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/god-rb.
For more options, visit https://groups.google.com/groups/opt_out.
