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Understanding the Port parameter

Reviewed on 02 April 2025 • Published on 02 April 2025

Port parameterLink to this anchor

The port of a containerized application refers to the network port that the application inside the container listens on for incoming requests.

When you deploy a container, you must map this internal port to a port on the host machine by specifying its value at container creation via the Port parameter. The value defined in this parameter will then be passed to your container during the deployment inside the PORT environment variable.

Note

Only one port can be exposed per Serverless Container.
Your container is accessible from the internet via ports 80 and 443, regardless of the specified port. The value you set determines how the Scaleway infrastructure accesses your container.

PORT environment variableLink to this anchor

To allow you application to be reachable, the port declared as a parameter when creating your Container must be the same as the port exposed by your containerized application.

We therefore recommend you use the $PORT variable in your application, as it will contain the port parameter value, as shown in the examples below.

nginx exampleLink to this anchor

FROM nginx:alpine
# Create a minimal nginx config that will be modified at runtime
RUN echo 'worker_processes 1; \
    events { worker_connections 1024; } \
    http { \
    server { \
    listen REPLACE_PORT default_server; \
    location / { return 200 "Hello from Nginx on Scaleway Serverless Containers!\n"; } \
    } \
    }' > /etc/nginx/nginx.conf
# Simple startup script that replaces the port
CMD ["/bin/sh", "-c", "sed -i s/REPLACE_PORT/$PORT/g /etc/nginx/nginx.conf && exec nginx -g 'daemon off;'"]

NodeJS exampleLink to this anchor

# Use the official Node.js slim image
FROM node:22-slim
# Create app directory
WORKDIR /usr/src/app
# Create package.json and simple Express app directly in Dockerfile
RUN echo '{"name":"scaleway-serverless","version":"1.0.0","description":"","main":"server.js","scripts":{"start":"node server.js"},"dependencies":{"express":"^5"}}' > package.json && \
    npm install && \
    echo "const express = require('express');\nconst app = express();\nconst port = process.env.PORT || 8080;\n\napp.get('/', (req, res) => {\n  res.send('<!DOCTYPE html><html><body><h1>Hello from Scaleway Serverless!</h1></body></html>');\n});\n\napp.listen(port, () => {\n  console.log(`Server running on port \${port}`);\n});" > server.js
# Start the application
CMD ["npm", "start"]

Python Flask exampleLink to this anchor

# Use the official Python slim image
FROM python:3.13-slim
# Install Flask
RUN pip install flask gunicorn
# Create a simple Flask app directly in the Dockerfile
RUN echo "from flask import Flask\napp = Flask(__name__)\n\n@app.route('/')\ndef hello():\n    return '<!DOCTYPE html><html><body><h1>Hello from Flask on Scaleway Serverless!</h1></body></html>'\n\nif __name__ == '__main__':\n    app.run(host='0.0.0.0', port=8080)" > app.py
# Run the app with Gunicorn
CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 app:app

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