Running a Flask API on an AWS Ubuntu instance is a common setup for web applications, but encountering issues like the API not responding from external sources can be frustrating. If your Flask app was working perfectly with curl requests, but suddenly stops responding from outside AWS, there are several potential causes to explore. This guide will walk you through the steps to identify and resolve the connection issue, whether it’s related to security group configurations, port access, or Flask settings.
Troubleshooting Flask API Accessibility in AWS
If your Flask API is not accessible from outside your AWS instance, but it works locally (e.g., with curl on localhost), there are a few things you can check. Below are steps to troubleshoot and fix the issue:
1. Check Flask Binding
By default, Flask binds to 127.0.0.1, which means it only accepts requests from localhost. To allow external access, you need to bind it to 0.0.0.0.
In your Flask app, modify the run method:
app.run(host='0.0.0.0', port=5000)This will allow the app to accept connections from any IP address.
2. Check Security Group
Ensure that your AWS EC2 security group allows inbound traffic on port 5000.
- Go to your EC2 console.
- Select your instance.
- Check the Inbound rules of your security group.
- Ensure there is an inbound rule for
TCP on port 5000from anyIP (0.0.0.0/0), or specify the IP range you need to allow.
3. Check Network ACLs
Verify that the network ACLs associated with your subnet are not blocking **inbound or outbound **traffic on port 5000. Ensure that both inbound and outbound rules allow traffic on port 5000.
4. Check EC2 Instance Firewall
If your **EC2 instance **is running a firewall like ufw (Uncomplicated Firewall), ensure that it’s configured to allow traffic on port 5000. Run the following command to allow traffic:
sudo ufw allow 5000/tcp5. Check CloudWatch Logs
Review your CloudWatch logs to check for any errors related to network connectivity or your Flask app. This can provide insights into whether your app is running properly or if there are issues preventing access.
6. Test with Curl from Outside AWS
After making the above changes, test the Flask API from an external machine by running the following command:
curl http://<your_aws_public_ip>:5000If everything is set up correctly, you should get a response from your Flask API.
By following the troubleshooting steps and reviewing your security group settings, you should be able to identify why your Flask API is no longer responding to external requests. Don’t forget to also check your Flask application’s configuration and the machine’s network settings. With a little persistence, you’ll have your Flask API up and running on AWS again. If the issue persists, consider reviewing your firewall rules or AWS instance configuration for any overlooked factors.