AWS App Runner freezing URL

This issue with AWS App Runner where the service shows as "Running" but the URL doesn't respond is something that several users have encountered. Based on your description, here are some potential causes and solutions:

1. Health Check Configuration: Even though your service shows as "Running," there might be a mismatch between your application's listening port and the port configured in App Runner. Verify that your Streamlit application is listening on the correct port (typically 8080 for App Runner by default) and that this matches your App Runner configuration.

2. Account-Specific Issues: In some cases, users have reported that their App Runner deployments failed repeatedly despite proper configuration. This could be due to account-specific quota restrictions. AWS Support has resolved similar issues through what they call an "account refresh." If you've tried other troubleshooting steps without success, contacting AWS Support might be necessary.

3. Platform Compatibility: If you built your Docker image on a different architecture (like an M1 Mac) than what App Runner uses (typically x86), this could cause issues. Try building with the --platform=linux/amd64 flag if you're using Docker.

4. Application Startup Time: Streamlit might be taking longer to initialize than the health check timeout allows. Try adjusting the health check timeout and interval settings.

5. Region-Specific Issues: Some users have reported intermittent issues in specific regions. As a test, you could try deploying your application in a different AWS region to see if the problem persists.

6. Service Pause/Resume: If your service was previously paused, try explicitly resuming it through the App Runner console by selecting "Actions" and then "Resume," even if it shows as "Running."

7. Host Header/SNI Issues: App Runner uses the Host header (for HTTP) or SNI (for HTTPS) to route requests. Make sure you're accessing the App Runner URL directly without any proxy or custom domain configuration that might interfere with these headers.

If none of these solutions work, you might want to try deploying a very simple non-Streamlit application (like a basic Flask app) to determine if the issue is specific to Streamlit or more general to your App Runner configuration.
Sources
AWS App Runner not passing health check for a simple python application | AWS re:Post
AWS APP RUNNER 404 possible ap-southeast-1 service level issue | AWS re:Post
Pausing and resuming an App Runner service - AWS App Runner
Why has Aws Runner failed to deploy the image even though it is working fine my local machine and everything configured properly | AWS re:Post