Security Monkey is another tool in Netflix’s Simian Army, which is a suite of tools designed to ensure that systems are being built in a resilient fashion. As well as providing a (configurable) assessment of any potential security vulnerabilities in your AWS setup, it can also be used to monitor changes on an ongoing basis, alerting different groups as required. It does overlap in some ways with AWS’ own Trusted Advisor Report and CloudTrail service, as it was developed prior to both these services being made generally available, but its capabilities do go beyond these offerings. If either of those services don’t quite meet your requirements, Security Monkey is worth a look.