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From your description, the service is down suddenly. I suppose you didn't change any EC2 configuration like SecurityGroup or NetworkACL.

1. I suggest you can check the health status of your instance first.

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/monitoring-system-instance-status-check.html#viewing_status

2. Do the self service check via look back IP address. (A) ssh Login to your instance. (B) Enter command: curl -v 127.0.0.1 and curl -v -k https://127.0.0.1 to confirm if your web service(Nginx/Apache) is able to response a http response.

If you encounter obstacles in these two places, the possible reasons are various issues within the OS. It is recommended that you seek further assistance from Linux/Windows experts based on the test results.