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The Flask web server (backend/web_server.py) supports configuration through environment variables, allowing you to customize the host, port, and debug mode without modifying code.

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Available Variables

The following environment variables are supported:
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HOST
string
default:"localhost"
The network interface to bind the Flask server to.
  • Use localhost or 127.0.0.1 for local-only access
  • Use 0.0.0.0 to accept connections from any network interface
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PORT
integer
default:"5000"
The port number for the Flask web server.
  • Default is 5000
  • Use a different port if 5000 is already in use
  • Must be between 1024 and 65535 for non-privileged users
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DEBUG
boolean
default:"true"
Enable or disable Flask debug mode.
  • true or True enables debug mode (automatic reloading, detailed errors)
  • false or False disables debug mode (recommended for production)

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Implementation Details

The Flask server reads these variables during startup:
web_server.py:184-186
def main():
    host = os.getenv('HOST', 'localhost')
    port = int(os.getenv('PORT', '5000'))
    debug = os.getenv('DEBUG', 'true').lower() == 'true'
The DEBUG variable performs a case-insensitive string comparison. Any value that doesn’t equal “true” (case-insensitive) will be treated as False.

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Setting Environment Variables

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One-time Execution

Set variables inline before the command:
HOST=0.0.0.0 PORT=8080 DEBUG=false python backend/web_server.py

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Export for Session

Export variables for the current terminal session:
export HOST=0.0.0.0
export PORT=8080
export DEBUG=false
python backend/web_server.py

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Permanent Configuration

Add to your shell profile (~/.bashrc, ~/.zshrc):
export HOST=0.0.0.0
export PORT=8080
export DEBUG=false
Then reload your profile:
source ~/.bashrc  # or ~/.zshrc

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Common Configurations

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Development (Default)

For local development with hot-reloading: 
HOST=localhost PORT=5000 DEBUG=true python backend/web_server.py
Expected output: 
✓ Iniciando servidor Flask...
✓ Conectado al servidor ICE en puerto 10000
✓ Servidor Flask escuchando en http://localhost:5000
  Para exponerlo con ngrok ejecuta: ngrok http 5000
 * Serving Flask app 'web_server'
 * Debug mode: on
Debug mode enables automatic code reloading and provides detailed error pages, making development faster.

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Network Access

To allow connections from other devices on your network: 
HOST=0.0.0.0 PORT=5000 DEBUG=true python backend/web_server.py
Your application will be accessible at:
  • http://localhost:5000 (local machine)
  • http://<your-ip>:5000 (other devices on the network)
Binding to 0.0.0.0 exposes your application to all network interfaces. Only use this on trusted networks.

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Production-like

For testing in production-like conditions: 
HOST=0.0.0.0 PORT=8080 DEBUG=false python backend/web_server.py
Flask’s built-in server is not recommended for production deployments. For production, use a WSGI server like Gunicorn or uWSGI.

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Custom Port

If port 5000 is occupied (common on macOS where AirPlay uses port 5000): 
PORT=8080 python backend/web_server.py

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Using with Automated Scripts

The automated run scripts (run.sh and run.ps1) don’t currently pass environment variables to the servers. To use custom configurations with the automated scripts, you can:

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Option 1: Modify the Scripts

Edit the run script to include environment variables: 
# Terminal 2: Flask Server
echo -e "${GREEN}[2/3] Levantando Flask Server en puerto 8080${NC}"
HOST=0.0.0.0 PORT=8080 DEBUG=false python3 web_server.py &
FLASK_PID=$!

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Option 2: Export Before Running

Export variables in your current shell session before running the script: 
export HOST=0.0.0.0
export PORT=8080
export DEBUG=false
./run.sh

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Verifying Configuration

When the Flask server starts, it prints the configuration: 
✓ Servidor Flask escuchando en http://localhost:5000
If you’ve changed the host or port, this message will reflect your changes: 
✓ Servidor Flask escuchando en http://0.0.0.0:8080
You can also check the debug mode status in the Flask startup messages: 
* Debug mode: on  # DEBUG=true
* Debug mode: off # DEBUG=false

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Connection String Format

The Flask server connects to the ICE server using a hardcoded connection string:
web_server.py:37-39
base = self.communicator.stringToProxy(
    "ConversorUnidades:default -p 10000"
)
The ICE server port (10000) is not configurable via environment variables. It’s hardcoded in both the server and client connection strings.

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Next Steps

Local Setup

Learn how to run the application locally

ngrok Tunnel

Expose your server to the internet

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