What is CloudTrail Logs?
Cloudtrail is an audit logs for the cloud tenant AWS API communication. It's created by default and retained for 90 Days. Each Log entry is an event. It only records the API Communication and it's also not a replacement of AV, EDR, MDR or XDR tools. For Instance,  CloudTrails logs can log the entry of another service accessing the EC2 but it will not log the other activity happened inside the EC2 Instance. All CloudTrail logs are recorded in UTC.

Default Log Retention Time?
90 Days (Free) - after 90 Days you should send/store it in S3 Bucket or Send it to your SIEM.

What can you do with CloudTrail?
The answer is a lot of things as far as Incident Investigation is concerned. Couple of common type answer you can find is:
 - What actions did a given user take over a specific time period?
​ - What is the source IP address for a particular activity?

Can you collect CloudTrail logs from all of your AWS Accounts and regions and put it in a centralized bucket?
Yes, you can do it while creating a new bucket for all your Cloudtrail Logs.

Detection Rules:
Disabled AWS CloudTrail logging

Splunk Queries:
index=aws-cloudtrail
| search NOT eventName in ("Des*", "List*","Get*")
| stats count values(eventName) by userIdentity.arn userIdentity.type userIdentity.accountId
| sort -count

IAM

AWS Inspector is used to list down all the Vulnerability as per the center of Internet security.

What is AWS CloudWatch? 
​One word: Performance Monitoring
AWS CloudWatch is a monitoring service to monitor your AWS Resources and the application that you run on AWS. CloudWatch is used for Performance Monitoring. It can monitor EC2, Autoscaling Groups, Elastic load Balancer, Route53, EBS, Storage gateway etc. It can also monitor Host Level Metrics like CPU, Network, Disk etc. 


CloudTrail vs CloudWatch
CloudTrails is like a CCTV and used for increasing the visibility for API Calls and CloudWatch Monitor Performance. 

Alerting
CloudWatch Alerting: Yes, you can create alerts in CloudWatch as well and trigger notifications for it. 

Security Use-Case

• Monitor and Notify on AWS Root User Activity. Link 
  • Video​
• Performance Monitoring of EC2 Instance for Anomaly Detection
  
  • Setup a CloudWatch to stream Data to a Centralized S3 Bucket. 

Additional Key things to remember

• CloudWatch can work with on-prem service as well. 
• Ensure that the Associated IAM policy has cloudwatch:putMetricData

Use AWS Config and Lambda to  Ensure that S3 Bucket Remains Private
 - AWS Config will trigger the Lambda Function to invoke SNS for any changes in the AWS.

Create a Lambda function to monitor the Bucket ACL and Bucket Policy Changes. If the bucket ACL found public - Lambda function can over write it to make it private. 
if the Bucket Policy found public - it can trigger a SNS Notification to the Security Team.

-- Cross region replication for the bucket ensures that the S3 Bucket is available in another region as well.

-- Use "AWS Encryption CLI" to encrypt the data first before sending  the data across the wire.