Difference between S3 Events and Cloudwatch Events

Question

I see this question has been asked few times but has not been answered yet. Making another attempt.

What is the basic difference between an S3 event and Cloudwatch events ? Is one is preferred over the other ?

Appreciate an answer.

Thanks !

Answer 1

S3 Event Notifications are for events that are specific to S3 buckets. S3 Events Notifications can publish events for

• New object created
• Object removal
• Restore object
• Reduced Redundancy Storage (RRS) object lost events
• Replication events

And it can send notifications to:

• SNS topics
• SQS queues
• Lambda functions

CloudWatch Events, and the associated (preferred, actually) service, Amazon EventBridge, are much broader, and apply to the entire AWS platform. CloudWatch and EventBridge use the same underlying CloudWatch Events API, but EventBridge has more features.

You can use CloudWatch Events/EventBridge to react to any event published by AWS CloudTrail as well as from a very long list of integrated AWS services. These events can also be published on a schedule using a cron-like schedule expression syntax. It can send notifications to more targets as well, including Amazon EC2, Kinesis data streams, ECS tasks, Systems Manager, and much more.

Generally, it's preferable to use EventBridge for anything other than S3. Since EventBridge shares the same underlying API as CloudWatch Events, any change you make to either one will show up in the other. You should use S3 Events for any of the events listed above (see the docs for up an to date list of events).