- No, there is no mentioned of EC2 having a CloudWatch agent installed in it by default in the documentation.
2/3. The EC2 service push the basic metrics such as CPU/Network Utilization and Disk Performance to CloudWatch. Having CW Agent installed in your EC2 offers access to the system level metrics:
Metrics collected by the CloudWatch agent - Metrics collected by the CloudWatch agent on Linux and macOS instances - https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/metrics-collected-by-CloudWatch-agent.html#linux-metrics-enabled-by-CloudWatch-agent
This also supports being able to collect the system level logs from your EC2 and be stored in CW Logs.
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