As already described in the :ref:`installation` section, no specific deployment procedures are for PyWPS when using flask-based server. But this formula is not intended to be used in a production environment. For production, Apache httpd or nginx servers are more advised. PyWPS is runs as a WSGI application on those servers. PyWPS relies on the Werkzeug library for this purpose.

PyWPS should be installed in your computer (as per the :ref:`installation` section). As a following step, you can now create several instances of your WPS server.

It is advisable for each PyWPS instance to have its own directory, where the WSGI file along with available processes should reside. Therefore create a new directory for the PyWPS instance:

$ sudo mkdir /path/to/pywps/

# create a directory for your processes too
$ sudo mkdir /path/to/pywps/processes

Each instance is represented by a single WSGI script (written in Python), which:

1. Loads the configuration files
2. Serves processes
3. Takes care about maximum number of concurrent processes and similar

An example WSGI script is distributed along with PyWPS-Demo service, as described in the :ref:`installation` section. The script is actually straightforward - in fact, it's a just wrapper around the PyWPS server with a list of processes and configuration files passed as arguments. Here is an example of a PyWPS WSGI script:

$ $EDITOR /path/to/pywps/pywps.wsgi

#!/usr/bin/env python3

from pywps.app.Service import Service

# processes need to be installed in PYTHON_PATH
from processes.sleep import Sleep
from processes.ultimate_question import UltimateQuestion
from processes.centroids import Centroids
from processes.sayhello import SayHello
from processes.feature_count import FeatureCount
from processes.buffer import Buffer
from processes.area import Area

processes = [
    FeatureCount(),
    SayHello(),
    Centroids(),
    UltimateQuestion(),
    Sleep(),
    Buffer(),
    Area()
]

# Service accepts two parameters:
# 1 - list of process instances
# 2 - list of configuration files
application = Service(
    processes,
    ['/path/to/pywps/pywps.cfg']
)

First, the WSGI module must be installed and enabled:

$ sudo apt-get install libapache2-mod-wsgi
$ sudo a2enmod wsgi

You then can edit your site configuration file (/etc/apache2/sites-enabled/yoursite.conf) and add the following:

# PyWPS
WSGIDaemonProcess pywps home=/path/to/pywps user=www-data group=www-data processes=2 threads=5
WSGIScriptAlias /pywps /path/to/pywps/pywps.wsgi process-group=pywps

<Directory /path/to/pywps/>
    WSGIScriptReloading On
    WSGIProcessGroup pywps
    WSGIApplicationGroup %{GLOBAL}
    Require all granted
</Directory>

And of course restart the server:

$ sudo service apache2 restart

We need nginx and gunicorn server:

$ apt install nginx-full
$ apt install gunicorn3

It is assumed that PyWPS is installed in your system (if not see: ref:installation) and we will used pywps-demo as installation example.

First, clonning the pywps-demo example to the root / (you need to be sudoer or root to run the examples):

$ cd /
$ git clone https://github.com/geopython/pywps-demo.git

Second, preparing the WSGI script for gunicorn. It is necessary that the WSGI script located on the pywps-demo is identified as a python module by gunicorn, this is done by creating a link with .py extention to the wsgi file:

$ cd /pywps-demo/wsgi
$ ln -s ./pywps.wsgi ./pywps_app.py

Gunicorn can already be tested by setting python path on the command options:

$ gunicorn3 -b 127.0.0.1:8081  --workers $((2*`nproc --all`)) --log-syslog  --pythonpath /pywps-demo wsgi.pywps_app:application

The command will start a gunicorn instance on the localhost IP and port 8081, logging to systlog (/var/log/syslog), using pywps process folder /pywps-demo/processes and loading module wsgi.pywps_app and object/function application for WSGI.

Next step is to configure NGINX, by pointing to the WSGI server by changing the location paths of the default site file but editing file /etc/nginx/sites-enabled as follows::

server {
     listen 80 default_server;
     listen [::]:80 default_server;
     server_name _;

     #better to redirect / to wps application
     location / {
     return 301 /wps;
     }

     location /wps {
             # with try_files active there will be problems
             #try_files $uri $uri/ =404;

             proxy_set_header Host $host;
             proxy_redirect          off;
             proxy_set_header        X-NginX-Proxy true;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
             proxy_pass http://127.0.0.1:8081;
             }

}

It is likely that part of the proxy configuration is already set on the file /etc/nginx/proxy.conf. Of course the necessatyrestart of nginx

$ service nginx restart

The service will now be available on the IP of the server or localhost

http://localhost/wps?request=GetCapabilities&service=wps

The current gunicorn instance was launched by the user. In a production server it is necessary to set gunicorn as a service

On ubuntu 16.04 the systemcltd system requires a service file that will start the gunicorn3 service. The service file (/lib/systemd/system/gunicorn.service) has to be configure as follows:

[Unit]
Description=gunicorn3 daemon
After=network.target

[Service]
User=www-data
Group=www-data
PIDFile=/var/run/gunicorn3.pid
Environment=WORKERS=3
ExecStart=/usr/bin/gunicorn3 -b 127.0.0.1:8081   --preload --workers $WORKERS --log-syslog --pythonpath /pywps-demo wsgi.pywps_app:application
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID

[Install]
WantedBy=multi-user.target

And then enable the service and then reload the systemctl daemon:

$ systemctl enable gunicorn3.service
$ systemctl daemon-reload
$ systemctl restart gunicorn3.service

And to check that everything is ok:

$ systemctl status gunicorn3.service

As stated, before, PyWPS should be available at http://localhost/pywps, we now can visit the url (or use wget):

# the --content-error parameter makes sure, error response is displayed
$ wget --content-error -O - "http://localhost/pywps"

The result should be an XML-encoded error message.

<?xml version="1.0" encoding="UTF-8"?>
<ows:ExceptionReport xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/ows/1.1 http://schemas.opengis.net/ows/1.1.0/owsExceptionReport.xsd" version="1.0.0">
    <ows:Exception exceptionCode="MissingParameterValue" locator="service">
        <ows:ExceptionText>service</ows:ExceptionText>
    </ows:Exception>
</ows:ExceptionReport>

The server responded with the :py:class:`pywps.exceptions.MissingParameterValue` exception, telling us that the parameter service was not set. This is compliant with the OGC WPS standard, since each request mast have at least the service and request parameters. We can say for now, that this PyWPS instance is properly deployed on the server, since it returns proper exception report.

We now have to configure the instance by editing the pywps.cfg file and adding some processes.