AWS S3 bucket logs vs AWS cloudtrail

Question

What's the difference between the AWS S3 logs and the AWS CloudTrail? On the doc of CloudTrail I saw this:

CloudTrail adds another dimension to the monitoring capabilities already offered by AWS. It does not change or replace logging features you might already be using.

Answer 1

AWS has added one more functionality since this question was asked, namely CloudTrail Data events

Currently there are 3 features available:

1. CloudTrail: Which logs almost all API calls at Bucket level Ref
2. CloudTrail Data Events: Which logs almost all API calls at Object level Ref
3. S3 server access logs: Which logs almost all (best effort server logs delivery) access calls to S3 objects. Ref

Now, 2 and 3 seem similar functionalities but they have some differences which may prompt users to use one or the other or both(in our case)! Below are the differences which I could find:

• Both works at different levels of granularity. e.g. CloudTrail data events can be set for all the S3 buckets for the AWS account or just for some folder in S3 bucket. Whereas, S3 server access logs would be set at individual bucket level
• The S3 server access logs seem to give more comprehensive information about the logs like BucketOwner, HTTPStatus, ErrorCode, etc. Full list

Information which is not available in Cloudtrail logs but is available in Server Access logs. Reference:

• Fields for Object Size, Total Time, Turn-Around Time, and HTTP Referer for log records
• Life cycle transitions, expiration, restores
• Logging of keys in a batch delete operation
• Authentication failures
• CloudTrail does not deliver logs for requests that fail authentication (in which the provided credentials are not valid). However, it does include logs for requests in which authorization fails (AccessDenied) and requests that are made by anonymous users.
• If a request is made by a different AWS Account, you will see the CloudTrail log in your account only if the bucket owner owns or has full access to the object in the request. If that is not the case, the logs will only be seen in the requester account. The logs for the same request will however be delivered in the server access logs of your account without any additional requirements.

AWS Support recommends that decisions can be made using CloudTrail logs and if you need that additional information too which is not available in CloudTrail logs, you can then use Server access logs.

Answer 2

CloudTrail tracks API access for infrastructure-changing events, in S3 this means creating, deleting, and modifying bucket (S3 CloudTrail docs). It is very focused on API methods that modify buckets.

S3 Server Access Logging provides web server-style logging of access to the objects in an S3 bucket. This logging is granular to the object, includes read-only operations, and includes non-API access like static web site browsing.

Answer 3

There are two reasons to use CloudTrail Logs over S3 Server Access Logs:

1. You are interested in bucket-level activity logging. CloudTrail has that, S3 logs does not.
2. You have a log analysis setup that involves CloudWatch log streams. The basic S3 logs just store log events to files on some S3 bucket and from there it's up to you to process them (though most log analytics services can do this for you).

Bottom line: use CloudTrail, which costs extra, if you have a specific scenario that requires it. Otherwise, the "standard" S3 Server Access Logs are good enough.

From the CloudTrail developer guide Logging Amazon S3 API calls using AWS CloudTrail:

Using CloudTrail Logs with Amazon S3 Server Access Logs and CloudWatch Logs

You can use AWS CloudTrail logs together with server access logs for Amazon S3. CloudTrail logs provide you with detailed API tracking for Amazon S3 bucket-level and object-level operations, while server access logs for Amazon S3 provide you visibility into object-level operations on your data in Amazon S3. For more information about server access logs, see Amazon S3 Server Access Logging.

You can also use CloudTrail logs together with CloudWatch for Amazon S3. CloudTrail integration with CloudWatch logs delivers S3 bucket-level API activity captured by CloudTrail to a CloudWatch log stream in the CloudWatch log group you specify. You can create CloudWatch alarms for monitoring specific API activity and receive email notifications when the specific API activity occurs. For more information about CloudWatch alarms for monitoring specific API activity, see the AWS CloudTrail User Guide. For more information about using CloudWatch with Amazon S3, see Monitoring Metrics with Amazon CloudWatch.

Answer 4

AWS CloudTrail is an AWS service for logging all account activities on different AWS resources. It also tracks things like IAM console login etc. Once CloudTrail service is enabled you can just go to CloudTrail console and see all the activity and also apply filters. Also, while enabling you can choose to log these activities and send the data to AWS CloudWatch. In AWS CloudWatch you can apply filters and also create alarms to notify you when a certain kind of activity happens.

S3 logging is enabling logging for basic activity on your S3 buckets/Objects.

Answer 5

CloudTrail logs API calls accessed to your AWS Account. These CloudTrail logs are stored in Amazon S3 Bucket.

The two offer different services.

The Definition you have shared from CloudTrail Doc: CloudTrail adds another dimension to the monitoring capabilities already offered by AWS. It does not change or replace logging features you might already be using.

It means you might have already activated some of the other logging features offered in other AWS services like ELB logging etc.. But when you enable CloudTrail monitoring, you need not worry about your previous logging functionalities as they will be still active. You will recieve logs from all the services. So By Enabling CloudTrail logging, It does not change or replace logging features you might already be using.

Hope it Helps.. :)