Answer two different questions
CloudTrail helps investigate activity and API calls in an AWS account. CloudWatch collects operational metrics and can receive logs from configured sources. A question such as “who changed the security group?” points toward CloudTrail; “when did application latency rise?” usually starts with CloudWatch metrics and application logs.
The tools can work together: a configured trail can deliver selected events to CloudWatch Logs for monitoring. That integration does not mean all possible events are automatically enabled or retained forever.
Select the evidence deliberately
CloudTrail event history covers recent management events, while a trail or other configured event data destination supports additional delivery and retention choices. Data events, such as specific object-level activity, require deliberate configuration and may have different costs. Confirm the event types, Regions and accounts relevant to the incident.
CloudWatch metrics need the right dimensions, period and statistic. A CPU graph alone cannot explain a failed deployment. Likewise, application logs appear only if an agent, service integration or application sends them to an appropriate log group.
Illustrative investigation
Suppose users report errors after a firewall change. Record the time window and affected account. Check relevant CloudTrail management events for the change, principal and request context. Compare that timeline with CloudWatch request errors, instance health and application logs. A timestamp match is a lead, not proof of causation: test the affected path and review the actual rule.
Retention and access
Set retention, encryption and access policies for each destination. Test that delivery works and that incident responders can read the records without broad write privileges. Avoid logging secrets and sensitive request bodies. Periodically verify the audit trail with a known harmless action and document who owns each log source.
Further reading
Read the official documentation. For help applying these checks, explore Clouvenix services.