last-steps.md

Last Steps

Port Rewrite

In order to make the web simulation work properly from the outside world over SSL, you have to configure your web server, session_server.py and simulation_server.py to perform port rewrite. Requests arriving to the web server will be redirected to the local network, e.g., wss://webserver.com/2000/client → ws://webserver.com:2000/client and https://webserver.com/2000/monitor → http://webserver.com:2000/monitor. You just need to have port 443 open in your local firewall for incoming connections. Such a setup is compatible with any client firewall allowing outgoing connections on port 443 to your server (which is very standard).

Port rewrite can be tested on a local host by setting up XAMPP to use SSL. In the session_server.py configuration, the simulationServers should be listed using the outside URL: hostname/2000 instead of hostname:2000. Your web server should be configured to redirect http traffic to https and to rewrite ports in URLs for both https and wss. With the Apache web server, this can be achieved by adding the following rules in your httpd.conf file:

%tab-component "generic"

%tab "webserver.com"

LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so
LoadModule proxy_wstunnel_module modules/mod_proxy_wstunnel.so

<VirtualHost *:80>
  ServerName webserver.com
  ServerAlias www.webserver.com

  [ ... ]

  RewriteEngine on

  # this rule redirect HTTP requests to HTTPS, removing the 'www.' prefix if any
  RewriteCond %{SERVER_NAME} =%{SERVER_NAME} [OR]
  RewriteCond %{SERVER_NAME} =www.%{SERVER_NAME}
  RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

<VirtualHost *:443>
  ServerName webserver.com
  ServerAlias www.webserver.com

  [ ... ]

  RewriteEngine on

  # this rule removes the 'www.' prefix from the hostname in the URL if any
  RewriteCond %{SERVER_NAME} =www.webserver.com
  RewriteRule ^ https://webserver.com%{REQUEST_URI} [END,NE,R=permanent]

  # port redirection rules (for session_server.py, simulation_server.py and webots)
  # websockets (should come first)
  RewriteCond %{HTTP:Upgrade} websocket [NC]
  RewriteCond %{HTTP:Connection} upgrade [NC]
  RewriteRule ^/(\d*)/(.*)$ "ws://%{SERVER_NAME}:$1/$2" [P,L]
  # http traffic (should come after websocket)
  RewriteRule ^/(\d*)/(.*)$ "http://%{SERVER_NAME}:$1/$2" [P,L]

</VirtualHost>

%tab-end

%tab "localhost"

LoadModule alias_module modules/mod_alias.so
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so
LoadModule proxy_wstunnel_module modules/mod_proxy_wstunnel.so

<VirtualHost *:80>
  ServerName localhost

  [ ... ]

  # this rule redirect HTTP requests to HTTPS
  Redirect "/" "https://localhost/"
</VirtualHost>

<VirtualHost *:443>
  ServerName localhost

  [ ... ]

  RewriteEngine on

  # port redirection rules (for session_server.py, simulation_server.py and webots)
  # websockets (should come first)
  RewriteCond %{HTTP:Upgrade} websocket [NC]
  RewriteCond %{HTTP:Connection} upgrade [NC]
  RewriteRule ^/(\d*)/(.*)$ "ws://%{SERVER_NAME}:$1/$2" [P,L]
  # http traffic (should come after websocket)
  RewriteRule ^/(\d*)/(.*)$ "http://%{SERVER_NAME}:$1/$2" [P,L]

</VirtualHost>

%tab-end

%end

Note: Port rewrite can be disabled for testing purposes in the session_server.py and simulation_server.py by simply setting the portRewrite configuration option to false.

Server Display

On Linux, a working Linux display (":0") should be available to run Webots remotely. This can be achieved generally simply by executing xhost + on the server computer.

Note: On some computers, in addition to the previous comment, the display entity is linked with the fact that a monitor is plugged. In this case, you can open automatically a user session when the computer is switched on, run session_server.py and simulation_server.py automatically when the session starts up, and let the monitor switched on at Ubuntu startup. If you have a headless system, i.e., a system without any physical monitors attached, then with the NVIDIA graphics card you could fake a monitor in the X session. This solution basically consists in adding a screen configuration to the X server configuration file by copying the Extended Display Identification Data (EDID) of a temporary attached monitor.

Startup Procedure

The startup procedure is the following:

1. Start all the simulation servers (simulation_server.py).
2. Start the session server (session_server.py).

This procedure should be automated in a startup script, so that the servers are restarted after a reboot of the machine.

The folder containing simulation_server.py and session_server.py should also contain a server.sh utility script to automatically start and stop both session_server.py and simulation_server.py with a given configuration file.

Please make sure that the WEBOTS_HOME variable is set before running the simulation and session server scripts.