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There are three best practice areas for Reliability in the cloud - Foundations, Change Management, Failure Management. Being aware of how change affects a system (change management) allows you to plan proactively, and monitoring allows you to quickly identify trends that could lead to capacity issues or SLA breaches.
AWS Config - AWS Config is a service that enables you to assess, audit, and evaluate the configurations of your AWS resources. Config continuously monitors and records your AWS resource configurations and allows you to automate the evaluation of recorded configurations against desired configurations.
How AWS Config Works:
via - https://aws.amazon.com/config/
AWS CloudTrail - AWS CloudTrail is a service that enables governance, compliance, operational auditing, and risk auditing of your AWS account. With CloudTrail, you can log, continuously monitor, and retain account activity related to actions across your AWS infrastructure. CloudTrail provides event history of your AWS account activity, including actions taken through the AWS Management Console, AWS SDKs, command-line tools, and other AWS services.
How CloudTrail Works:
via - https://aws.amazon.com/cloudtrail/
Amazon CloudWatch - Amazon CloudWatch is a monitoring and observability service built for DevOps engineers, developers, site reliability engineers (SREs), and IT managers. CloudWatch provides data and actionable insights to monitor applications, respond to system-wide performance changes, optimize resource utilization, and get a unified view of operational health.
Incorrect options:
AWS Trusted Advisor - AWS Trusted Advisor is an online tool that provides you real-time guidance to help you provision your resources following AWS best practices on cost optimization, security, fault tolerance, service limits, and performance improvement.
Amazon Inspector - 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 exposure, vulnerabilities, and deviations from best practices.
Amazon GuardDuty - Amazon GuardDuty is a threat detection service that monitors malicious activity and unauthorized behavior to protect your AWS account. GuardDuty analyzes billions of events across your AWS accounts from AWS CloudTrail (AWS user and API activity in your accounts), Amazon VPC Flow Logs (network traffic data), and DNS Logs (name query patterns). This service is for AWS account level access, not for instance-level management like an EC2. GuardDuty cannot be used to check OS vulnerabilities.
References:
https://d1.awsstatic.com/whitepapers/architecture/AWS_Well-Architected_Framework.pdf
https://aws.amazon.com/config/
https://aws.amazon.com/cloudtrail/