Using WSGI with Nova

Changed in version 33.0.0: Removed support for the eventlet server scripts, nova-api, nova-api-metadata and nova-api-os-compute. Only WSGI-based deployments are supported going forward and it is no longer possible to run the compute API and metadata APIs in the same process, as it was with the eventlet scripts.

Changed in version 33.0.0: Removed the nova-api-wsgi and nova-metadata-wsgi WSGI scripts previously provided by Nova. Deployment tooling should instead reference the Python module paths for these services, nova.wsgi.osapi_compute and nova.wsgi.metadata, if their chosen WSGI server supports this (gunicorn, uWSGI) or implement a .wsgi script themselves if not (mod_wsgi).

Nova provides two APIs: a compute API (a.k.a. the REST API) and a metadata API. Both of these APIs are implemented as generic Python HTTP servers that implement WSGI and are expected to be deployed using a server with WSGI support.

To facilitate this, Nova provides a WSGI module for each API that provide the application object that most WSGI servers require. These can be found at nova.wsgi.osapi_compute and nova.wsgi.metadata for the compute API and the metadata API, respectively. The application objects are automatically configured with configuration from nova.conf and api-paste.ini by default, and the the config files and config directory can be overridden via the OS_NOVA_CONFIG_FILES and OS_NOVA_CONFIG_DIR environment variables.

Note

File paths listed in OS_NOVA_CONFIG_FILES are relative to OS_NOVA_CONFIG_DIR and delimited by ;.

DevStack deploys the compute and metadata APIs behind Apache using 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. It is up to you, as a deployer, to choose an appropriate server for your deployment.