Re: [Pythomnic3k-questions] Best Practice to Auto-Start cages under Linux

[<dm...@ta...>]

Hi Eric,

I can give you an example which you should be able to incorporate into 
your rc.d start/stop framework.

A few words about shutting down a Pythomnic application in general.

First, there actually are two python processes - one "external", which 
executes
startup.py and whose pid you have in cages/foo/logs/foo.pid and one 
"internal" which
actually executes your application. External process monitors the 
internal one and restarts it if it crashes. Therefore you don't have 
access to the internal process directly.

Second, shutting down is not immediate. When a shutdown is initiated, 
all the interfaces are signaled to stop accepting requests, but the 
requests already being executed are allowed to finish. This means that 
in the worst case shutdown process can take up to "request_timeout" 
seconds.

As to how it is done. You kill the external process using its pid and 
then wait for the internal process to complete shutdown. The former is 
easy, and the latter is ugly, because you have no pid for the external 
process. As a hack, you could tail the log file until successful 
shutdown message appears in it.

So, something like this:

---

cage=foo
timeout=10

/bin/echo -n "shutting down $cage:"

kill `cat pythomnic3k/cages/$cage/logs/$cage.pid`

for i in `jot - $timeout 0`; do

     tail pythomnic3k/cages/$cage/logs/$cage-`date +%Y%m%d`.log | grep -q 
'properly shut down' && /bin/echo 'ok' && break

     if [ $i -eq 0 ]; then
         /bin/echo 'timeout'
         break
     fi

     /bin/echo -n '.' && sleep 1

done

---


Dmitry

On 22.01.2016 10:18, Eric Livingston wrote:
> Dmitry,
> 
> Do you have a handy template script that can start/stop cages under
> linux (Debian Wheezy, in this case, so the rc.d structure) as you can
> other services? I'd like to be able to something like
> "/etc/init.d/cage start" and "stop" and put in in the default startup
> sequence, etc.
> 
> Starting a cage is easy, but I can't find a good way to cleanly shut
> one down, unless startup.py also doubles as "shutdown.py"!
> 
> Eric
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