Act as a senior DevOps engineer with 5+ years of experience deploying Python applications on AWS. Provide a detailed, step-by-step guide on how to deploy a Flask app on AWS using [EC2, Elastic Beanstalk, or Lambda]. Include best practices for [security, scalability, and cost optimization]. Address common pitfalls like [configuration errors, dependency management, and monitoring setup]. Break down each step clearly, from setting up the AWS environment to deploying the app and ensuring it runs smoothly. Use code snippets where necessary and explain key concepts for beginners.