To get a deep dive on CloudWatch Metrics and get a complete hands-on experience on this topic, head to the Metrics module
ECS/ContainerInsights. All metrics collected collected by CloudWatch Container Insights from all ECS clusters in that region are grouped here.
Inside there, you should be 3 different dimensions under which metrics are collected as shown below.
If you have a cluster that uses EC2 launch type you can also enable the CloudWatch Agent to collect metrics at instance level