CloudWatch

Amazon CloudWatch is the default place where AWS services publish their metrics and where applications send their logs. Most monitoring on AWS starts here, even when a dashboard or alerting tool elsewhere is the thing people look at.

Start with CloudWatch for what is collected without any setup and what needs the CloudWatch agent. The gap between the two — memory and disk usage on EC2 are the usual surprise — is where most monitoring blind spots come from.

CloudWatch Logs covers how log data is organised, retained, and turned into metrics and alarms. CloudWatch Logs Insights covers querying that data: the supported query languages, what queries cost, and when X-Ray, OpenSearch or Grafana is the better tool for the question.