Using WSGI with Nova

Though the compute and metadata APIs can be run using independent scripts that provide eventlet-based HTTP servers, it is generally considered more performant and flexible to run them using a generic HTTP server that supports WSGI (such as Apache or nginx).

The nova project provides two automatically generated entry points that support this: nova-api-wsgi and nova-metadata-wsgi. These read nova.conf and api-paste.ini by default and generate the required module-level application that most WSGI servers require. If nova is installed using pip, these two scripts will be installed into whatever the expected bin directory is for the environment.

The config files and config directory can be overridden via the OS_NOVA_CONFIG_FILES and OS_NOVA_CONFIG_DIR environment variables. File paths listed in OS_NOVA_CONFIG_FILES are relative to OS_NOVA_CONFIG_DIR and delimited by ;.

The new scripts replace older experimental scripts that could be found in the nova/wsgi directory of the code repository. The new scripts are not experimental.

When running the compute and metadata services with WSGI, sharing the compute and metadata service in the same process is not supported (as it is in the eventlet-based scripts).

In devstack as of May 2017, the compute and metadata APIs are hosted by a Apache communicating with uwsgi via mod_proxy_uwsgi. Inspecting the configuration created there can provide some guidance on one option for managing the WSGI scripts. It is important to remember, however, that one of the major features of using WSGI is that there are many different ways to host a WSGI application. Different servers make different choices about performance and configurability.