Explanation

According to the AWS Shared Responsibility Model:

• AWS is responsible for "Security OF the Cloud" - This includes:

  • Protecting and securing the AWS global infrastructure
  • Maintaining the physical hardware
  • Securing the underlying virtualization infrastructure
  • Patching and maintaining AWS managed services like Amazon RDS

• Customers are responsible for "Security IN the Cloud" - This includes:

  • Patching the guest operating system of EC2 instances
  • Managing security groups and network access control lists
  • Managing IAM users and permissions
  • Encrypting data at rest and in transit
  • Application-level security

Therefore, patching the guest operating system of Amazon EC2 instances is clearly a customer responsibility, while the other options (hardware security, AWS global infrastructure protection, and RDS patching) are AWS responsibilities.