Each of the account activity is called a CloudTrail event
CloudTrail by default stores 90 days of event history for no cost. By default it does not save to S3
To customize a new Trail needs to be created
Events are of 3 types
Management Events aka ControlPlane Operations
Data Events
Insight Events
By default Cloud Trail logs only Management Events
A custom trail can be created as a single region trail or all region trail
All region trail is a collection of trails in each region but managed at one place. Any new regions added by AWS get automatically added to this
Additionally for Global Services(IAM,STS,CloudFront) which log events only to 1 region i.e. US East 1 Cloud Trail needs to be specifically configured to store them
A trail stores its events in an S3 bucket as json files
CloudTrail can also send its events to CWL
An organizational trail when created stores events for all accounts within that organization
Cloud Trail is not real time service. Events are logged within 15 minutes of activity