AWS Cost Explorer is a tool that helps analyze AWS costs and usage over time. It enables rightsizing by identifying underutilized resources and recommending appropriate instance types to optimize costs while maintaining performance. Rightsizing is the process of matching instance types and sizes to workload performance and capacity requirements at the lowest possible cost.

• Reliability refers to a system's ability to recover from failures and continue functioning
• Resilience is about a system's ability to withstand and recover from disruptions
• Modernization involves updating legacy systems to use cloud-native technologies

Cost Explorer specifically supports rightsizing through its cost optimization recommendations and resource utilization analysis.