Open Stack

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Hi,

> I will take a look to the neutron code, if I found a rpc usage
> before the os.fork().

With a basic devstack that use the ml2 plugin, I found at least two rpc 
usage before the os.fork() in neutron:

https://github.com/openstack/neutron/blob/master/neutron/services/l3_router/l3_router_plugin.py#L63
https://github.com/openstack/neutron/blob/master/neutron/services/loadbalancer/drivers/common/agent_driver_base.py#L341


It looks like all services plugins run into the parent thread, and only 
the core plugin (ml2) run in children ... rpc_workers apply only on the 
core plugin rpc code... not for other plugins.

If I correctly understand, neutron server does:
- - load and start wsgi server (in a eventlet thread)
- - load neutron manager that:
   * load core plugin
   * load services plugins
   * start services plugins (some rpc connections are created)
- - fork neutron-server (by using the ProcessLauncher)
- - drop the DB connections of children to ensure oslo.db created new 
ones (looks like releases connection already opened by the parent 
process)
- - start core plugin rpc connections of children

It seems the wsgi code and service plugins live in each children but do 
nothing...

I think ProcessLauncher is more designed to bootstrap many identical 
processes with a parent process that do nothing (except child 
start/stop).

For oslo.messaging, perhaps we needs to document when we can fork and 
when it's too late to fork the process when it use oslo.messaging.


Cheers,

- ---
Mehdi Abaakouk
mail: sileht at sileht.net
irc: sileht
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