openstack/nova
Code Issues Proposed changes

[placement] Update the placement deployment instructions

Browse Source 
The web-server-deployment section of placement.rst has been updated
to provide additional links to information and reflect the fact that
placement is now using uwsgi and mod_proxy_uwsgi in devstack. This
does not provide a full set of installations instructions. This is
somewhat intentional:

* there are many ways to deploy a wsgi application and we'd like the
  packagers and deployers to choose a way that works best for them,
  not impose one, and there's no way for us to document them all. It
  is better to point to resources that explain some of the options
  and allow people to inform themselves so they can make informed
  choices
* we're no longer that keen on the mod_wsgi, but it tends to be the
  easiest to document (fewer moving parts)
* the uwsgi+systemd method in devstack, while great, is abstracted
  enough that the moving parts are not entirely visible and is one
  of several ways for that scenario

Change-Id: Ief07c313e012df63558de632047258e8e11736c1
Related-Bug: #1692375
This commit is contained in:
Chris Dent 2017-09-28 14:14:55 +01:00
parent 1aa1462b98
commit 3a9afe608f
1 changed files with 58 additions and 17 deletions
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75
doc/source/user/placement.rst
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@ -69,16 +69,69 @@ Steps
**1. Deploy the API service**
At this time the placement API code is still in Nova alongside the compute
REST API code (nova-api). So once you have upgraded nova-api to Newton you
already have the placement API code, you just need to install the service.
Nova provides a ``nova-placement-api`` WSGI script for running the service
with Apache.
At this time the placement API code is still in Nova alongside the compute REST
API code (nova-api). So once you have upgraded nova-api to Newton you already
have the placement API code, you just need to install the service. Nova
provides a ``nova-placement-api`` WSGI script for running the service with
Apache, nginx or other WSGI-capable web servers. Depending on what packaging
solution is used to deploy OpenStack, the WSGI script may be in ``/usr/bin``
or ``/usr/local/bin``.
.. note:: The placement API service is currently developed within Nova but
it is designed to be as separate as possible from the existing code so
that it can eventually be split into a separate project.
``nova-placement-api``, as a standard WSGI script, provides a module level
``application`` attribute that most WSGI servers expect to find. This means it
is possible to run it with lots of different servers, providing flexibility in
the face of different deployment scenarios. Common scenarios include:
* apache2_ with mod_wsgi_
* apache2 with mod_proxy_uwsgi_
* nginx_ with uwsgi_
* nginx with gunicorn_
In all of these scenarios the host, port and mounting path (or prefix) of the
application is controlled in the web server's configuration, not in the
configuration (``nova.conf``) of the placement application.
When placement was `first added to DevStack`_ it used the ``mod_wsgi`` style.
Later it `was updated`_ to use mod_proxy_uwsgi_. Looking at those changes can
be useful for understanding the relevant options.
DevStack is configured to host placement at ``/placement`` on either the
default port for http or for https (``80`` or ``443``) depending on whether TLS
is being used. Using a default port is desirable.
By default, the placement application will get its configuration for settings
such as the database connection URL from ``/etc/nova/nova.conf``. The directory
the configuration file will be found in can be changed by setting
``OS_PLACEMENT_CONFIG_DIR`` in the environment of the process that starts the
application.
.. note:: When using uwsgi with a front end (e.g., apache2 or nginx) something
needs to ensure that the uwsgi process is running. In DevStack this is done
with systemd_. This is one of many different ways to manage uwsgi.
This document refrains from declaring a set of installation instructions for
the placement service. This is because a major point of having a WSGI
application is to make the deployment as flexible as possible. Because the
placement API service is itself stateless (all state is in the database), it is
possible to deploy as many servers as desired behind a load balancing solution
for robust and simple scaling. If you familiarize yourself with installing
generic WSGI applications (using the links in the common scenarios list,
above), those techniques will be applicable here.
.. _apache2: http://httpd.apache.org/
.. _mod_wsgi: https://modwsgi.readthedocs.io/
.. _mod_proxy_uwsgi: http://uwsgi-docs.readthedocs.io/en/latest/Apache.html
.. _nginx: http://nginx.org/
.. _uwsgi: http://uwsgi-docs.readthedocs.io/en/latest/Nginx.html
.. _gunicorn: http://gunicorn.org/
.. _first added to DevStack: https://review.openstack.org/#/c/342362/
.. _was updated: https://review.openstack.org/#/c/456717/
.. _systemd: https://review.openstack.org/#/c/448323/
**2. Synchronize the database**
In the Newton release the Nova **api** database is the only deployment
@ -124,18 +177,6 @@ placement-api service.
updated in the ``[placement]`` group for credentials to make requests
from nova-compute to the placement-api service.
References
~~~~~~~~~~
The following changes were made to devstack (from oldest to newest) to enable
the placement-api service and can serve as a guide for your own deployment.
https://review.openstack.org/#/c/342362/
https://review.openstack.org/#/c/363335/
https://review.openstack.org/#/c/363724/
Upgrade Notes
=============