Web app in AWS EC2 instance server cannot be visited

Question

Our web apps running at AWS EC2 instance server suddently cannot be visited.  The apps can be started successfully, but when visiting them in browser, we got '400 Bad request version' error all the time.
We tried to reboot instance several times, we tried to create some very simple node.js or react sites, we tried to run them on different ports, but still got same problem.
Our app were running well in port 5000, 5001, etc.  We created security group for inbound ports already.
Can anyone help?

Answer

Hello.

Since it is a 400 error, I think it is an error that occurs when there is some problem with the request method from the client.  
For troubleshooting purposes, you will need to check the access logs and error logs of the web server and application.

Web app in AWS EC2 instance server cannot be visited

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