WSGI Usage with the Neutron API

This document is a guide to deploying Neutron using WSGI. There are two ways to deploy using WSGI: uwsgi and Apache mod_wsgi.

Please note that if you intend to use mode uwsgi, you should install the mode_proxy_uwsgi module. For example on deb-based system:

# sudo apt-get install libapache2-mod-proxy-uwsgi
# sudo a2enmod proxy
# sudo a2enmod proxy_uwsgi

WSGI Application

The function neutron.server.get_application will setup a WSGI application to run behind uwsgi and mod_wsgi.

Neutron API behind uwsgi

Create a /etc/neutron/neutron-api-uwsgi.ini file with the content below:

chmod-socket = 666
socket = /var/run/uwsgi/neutron-api.socket
lazy-apps = true
add-header = Connection: close
buffer-size = 65535
hook-master-start = unix_signal:15 gracefully_kill_them_all
thunder-lock = true
plugins = python
enable-threads = true
worker-reload-mercy = 90
exit-on-reload = false
die-on-term = true
master = true
processes = 2
wsgi-file = <path-to-neutron-bin-dir>/neutron-api

Start neutron-api:

# uwsgi --procname-prefix neutron-api --ini /etc/neutron/neutron-api-uwsgi.ini

Neutron API behind mod_wsgi

Create /etc/apache2/neutron.conf with content below:

Listen 9696
LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\" %D(us)" neutron_combined

<Directory /usr/local/bin>
    Require all granted

<VirtualHost *:9696>
    WSGIDaemonProcess neutron-server processes=1 threads=1 user=stack display-name=%{GROUP}
    WSGIProcessGroup neutron-server
    WSGIScriptAlias / <path-to-neutron-bin-dir>/neutron-api
    WSGIApplicationGroup %{GLOBAL}
    WSGIPassAuthorization On
    ErrorLogFormat "%M"
    ErrorLog /var/log/neutron/neutron.log
    CustomLog /var/log/neutron/neutron_access.log neutron_combined

Alias /networking <path-to-neutron-bin-dir>/neutron-api
<Location /networking>
    SetHandler wsgi-script
    Options +ExecCGI
    WSGIProcessGroup neutron-server
    WSGIApplicationGroup %{GLOBAL}
    WSGIPassAuthorization On

WSGISocketPrefix /var/run/apache2

For deb-based systems copy or symlink the file to /etc/apache2/sites-available. Then enable the neutron site:

# a2ensite neutron
# systemctl reload apache2.service

For rpm-based systems copy the file to /etc/httpd/conf.d. Then enable the neutron site:

# systemctl reload httpd.service

Start Neutron RPC server

When Neutron API is served by a web server (like Apache2) it is difficult to start an rpc listener thread. So start the Neutron RPC server process to serve this job:

# /usr/bin/neutron-rpc-server --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugins/ml2/ml2_conf.ini

Neutron Worker Processes

Neutron will attempt to spawn a number of child processes for handling API and RPC requests. The number of API workers is set to the number of CPU cores, further limited by available memory, and the number of RPC workers is set to half that number.

It is strongly recommended that all deployers set these values themselves, via the api_workers and rpc_workers configuration parameters.

For a cloud with a high load to a relatively small number of objects, a smaller value for api_workers will provide better performance than many (somewhere around 4-8.) For a cloud with a high load to lots of different objects, then the more the better. Budget neutron-server using about 2GB of RAM in steady-state.

For rpc_workers, there needs to be enough to keep up with incoming events from the various neutron agents. Signs that there are too few can be agent heartbeats arriving late, nova vif bindings timing out on the hypervisors, or rpc message timeout exceptions in agent logs (for example, “broken pipe” errors).

There is also the rpc_state_report_workers option, which determines the number fo RPC worker processes dedicated to process state reports from the various agents. This may be increased to resolve frequent delay in processing agents heartbeats.


If OVN ML2 plugin is used without any additional agents, neutron requires no worker for RPC message processing. Set both rpc_workers and rpc_state_report_workers to 0, to disable RPC workers.