Flask application: Same source code on AWS Lightsail (Ubuntu) showing internal server error once the form submitted though working fine on VS Code

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http://44.206.118.123:8080/ For the Flask application, same source code on AWS Lightsail (Ubuntu) showing internal server error once the form submitted though working fine on VS Studio (https://www.canva.com/design/DAGIZJrhyIk/EYzsYG5sfXMmEazS77EQ1w/edit?utm_content=DAGIZJrhyIk&utm_campaign=designshare&utm_medium=link2&utm_source=sharebutton). What could be the reason?

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asked 8 months ago337 views
1 Answer
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Greeting

Hi Rajeev!

Thanks for reaching out and sharing the details of your issue with your Flask application on AWS Lightsail. It’s clear you’ve put effort into replicating the code on VS Code, where it works perfectly, so let’s dive into resolving the internal server error you’re facing after form submission.


Clarifying the Issue

From what you've described, your Flask application behaves as expected on your local VS Code setup but throws an internal server error when deployed on AWS Lightsail (Ubuntu). This suggests that the issue might not lie in your code itself but instead in the deployment environment, configurations, or permissions on Lightsail. Lightsail, known for its simplicity compared to EC2, is designed for lightweight deployments, but occasional configuration nuances can lead to errors like this. Let’s address them step-by-step.


Key Terms

  • Flask: A Python-based web framework for building applications.
  • AWS Lightsail: A cloud platform for deploying lightweight virtual servers.
  • Internal Server Error (500): A generic error indicating a problem with the server processing the request.
  • Deployment Environment: The system (e.g., OS, libraries) where the application is hosted.
  • WSGI (Web Server Gateway Interface): A standard interface between web servers (like Nginx) and Python applications (like Flask). It acts as a bridge, ensuring compatibility and efficient communication during deployments.

The Solution (Our Recipe)

Steps at a Glance:

  1. Review Flask Logs.
  2. Verify Python and Flask Versions.
  3. Check Permissions and File Ownership.
  4. Update Environment Variables.
  5. Confirm Correct WSGI Configuration.
  6. Test Endpoint Accessibility.
  7. Implement Staging Environment Testing (Optional but Recommended).

Step-by-Step Guide:

  1. Review Flask Logs:
    Check the application logs to pinpoint the issue causing the internal server error. Run the following command in the terminal:
    tail -f /var/log/your_flask_app.log
    If you are using systemd to manage your service, access the logs with:
    journalctl -u your_app.service -f

  1. Verify Python and Flask Versions:
    Ensure that your Python version and Flask version on Lightsail match your local environment. Use these commands:
    python3 --version
    pip show flask

  1. Check Permissions and File Ownership:
    Ensure the Flask application files and directories have the correct permissions and ownership. Run the following:
    sudo chmod -R 755 /path/to/your/app
    sudo chown -R www-data:www-data /path/to/your/app

  1. Update Environment Variables:
    Ensure that all necessary environment variables are set correctly. You can set them temporarily with:
    export FLASK_ENV=production
    Alternatively, edit a .env file in your application directory with:
    FLASK_ENV=production
    DATABASE_URL=your_database_url

  1. Confirm Correct WSGI Configuration:
    Check your WSGI file (e.g., wsgi.py) to ensure it properly references your Flask app. An example WSGI script looks like this:
    from your_app import app
    
    if __name__ == "__main__":
        app.run()
    Restart your server after making changes:
    sudo systemctl restart your_app.service

  1. Test Endpoint Accessibility:
    Test your application endpoints to ensure they are accessible. Use curl to verify the output:
    curl http://your-ip-address:8080

  1. Implement Staging Environment Testing (Optional but Recommended):
    Before making changes to your production Lightsail instance, consider creating a staging environment. In Lightsail, you can easily create a snapshot of your existing instance and deploy it as a new instance for testing:
    # Create a snapshot in the Lightsail dashboard
    This ensures that any adjustments you make won’t impact your live application until thoroughly tested.

Closing Thoughts

Rajeev, these steps should help you diagnose and resolve the internal server error with your Flask application on AWS Lightsail. By addressing logs, configurations, and environment variables, you can eliminate common culprits and pinpoint the root cause. Leveraging staging environments will also give you confidence in any changes before they reach production. If the issue persists, feel free to share the specific error logs or configuration details, and I’d be happy to assist further. You’ve got this! 🚀


Farewell

Best regards, Rajeev, and happy coding!


Cheers,

Aaron 😊

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answered 2 months ago

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