d92d093418
Unlike uwsgi, apache mod_wsgi does not support passing
commandline arguments to the python wsgi script it invokes.
As a result while you can pass --config-file when hosting the
api and metadata wsgi applications with uwsgi there is no
way to use multiple config files with mod_wsgi.
This change mirrors how this is supported in keystone today
by intoducing a new OS_NOVA_CONFIG_FILES env var to allow
operators to optional pass a ';' delimited list of config
files to load.
This change also add docs for this env var and the existing
undocumented OS_NOVA_CONFIG_DIR.
Closes-Bug: 1994056
Change-Id: I8e3ccd75cbb7f2e132b403cb38022787c2c0a37b
(cherry picked from commit 73fe84fa0e)
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Using WSGI with Nova
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====================
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Though the compute and metadata APIs can be run using independent scripts that
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provide eventlet-based HTTP servers, it is generally considered more performant
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and flexible to run them using a generic HTTP server that supports WSGI_ (such
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as Apache_ or nginx_).
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The nova project provides two automatically generated entry points that
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support this: ``nova-api-wsgi`` and ``nova-metadata-wsgi``. These read
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``nova.conf`` and ``api-paste.ini`` by default and generate the required
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module-level ``application`` that most WSGI servers require.
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If nova is installed using pip, these two scripts will be installed into
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whatever the expected ``bin`` directory is for the environment.
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The config files and config directory can be overridden via the
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``OS_NOVA_CONFIG_FILES`` and ``OS_NOVA_CONFIG_DIR`` environment variables.
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File paths listed in ``OS_NOVA_CONFIG_FILES`` are relative to
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``OS_NOVA_CONFIG_DIR`` and delimited by ``;``.
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The new scripts replace older experimental scripts that could be found in the
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``nova/wsgi`` directory of the code repository. The new scripts are *not*
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experimental.
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When running the compute and metadata services with WSGI, sharing the compute
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and metadata service in the same process is not supported (as it is in the
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eventlet-based scripts).
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In devstack as of May 2017, the compute and metadata APIs are hosted by a
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Apache communicating with uwsgi_ via mod_proxy_uwsgi_. Inspecting the
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configuration created there can provide some guidance on one option for
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managing the WSGI scripts. It is important to remember, however, that one of
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the major features of using WSGI is that there are many different ways to host
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a WSGI application. Different servers make different choices about performance
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and configurability.
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.. _WSGI: https://www.python.org/dev/peps/pep-3333/
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.. _apache: http://httpd.apache.org/
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.. _nginx: http://nginx.org/en/
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.. _uwsgi: https://uwsgi-docs.readthedocs.io/
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.. _mod_proxy_uwsgi: http://uwsgi-docs.readthedocs.io/en/latest/Apache.html#mod-proxy-uwsgi
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