AWS deployment for a single container shows Severe Health Status

Hi, I have an issue with AWS deployment for a single container that shows Severe Health Status. I followed one to one the instruction, but once I uploaded the aws.json file, the AWS server didn't start. I am new to AWS deployment and couldn't find any log file to understand the error exactly. All GUI messages are not descriptive enough. I need to install EB CLI to retrieve the log files. Could you navigate me what exactly I need to do and to look for to understand the issue? The flask app is so simple, and it runs locally. The aws.json file is correct and the same as in the instruction. I have no idea what is wrong with AWS. It is frustrating to get errors on such a simple example. Thanks