Looking for ways to host application in AWS and have it monitored using opensource
You can try built-in tools that provide by AWS.
AWS calls them Management Tools.

Amazon Inspector

Automated security assessment service to help improve the security and compliance of applications deployed on AWS.
Amazon Inspector is an automated security assessment service that helps improve the security and compliance of applications deployed on AWS. Amazon Inspector automatically assesses applications for vulnerabilities or deviations from best practices. After performing an assessment, Amazon Inspector produces a detailed list of security findings prioritized by level of severity. These findings can be reviewed directly or as part of detailed assessment reports which are available via the Amazon Inspector console or API.
— AWS Inspector

Amazon Web Services (AWS) Monitoring With Nagios

Implementing effective Amazon Web Services monitoring with Nagios
offers the following benefits:
Increased server, services, and application availability Fast
detection of network outages Fast detection of cloud computing
environment problems
— Nagios

Some other tools:

Scalr

Management Tools by AWS