1. AWS events comes to default event bus. We defined a rule and a role to catch the indicated events. This definitions should be in all accounts which you want to observe. The file under cross-account-permissions folder should be added to all accounts and other files should be added to monitoring account.
2. Gave our custom bus as a target for other event busses (in aws_cloudwatch_event_target). Also, our custom bus calls own target (lambda function).
3. If any ECS task shuts down suddenly, lambda function checks the cases. If this is an unexpected situation, sends all the necessary informations to slack channel.