S3 Events: Unlocking your Imagination

S3 can trigger automated actions when things happen in a bucket. Upload a file, delete one, restore from glacier - you can hook into all of that and kick off other processes.

The typical setup involves an S3 bucket, an event type (object created, deleted, restored), a destination (Lambda, SQS, or SNS), and you’re rolling.

Use Cases

Here is where things get interesting. A few patterns I have seen work well in production:

Image and video processing - When someone uploads a file to S3, you can spin up a Lambda to resize thumbnails, compress images, or transcode video without managing any servers. The processing runs in response to each upload.

Log processing - applications upload logs to S3 and a Lambda picks them up to parse, filter, or ship to Elasticsearch or a data warehouse. This keeps a real-time stream without polling.

Real-time data pipelines - IoT sensors, clickstreams, transaction feeds - all can land in S3 and trigger lightweight transformations. Lambda is fine for smaller workloads; for heavier lifting you would route to something like Kinesis.

Backup workflows - New files in a bucket can trigger cross-region replication or copy operations to a disaster recovery bucket.

These are common patterns, not an exhaustive list. The event-driven approach works wherever you want actions tied to data landing.

Receive Notifications on your Phone

Here is a practical example. You want an SMS when a specific file changes in S3.

1. Create an SNS topic - name it something like “S3 File Change Alerts” and copy the ARN.
2. Create or pick an S3 bucket to monitor.
3. In the S3 console, go to Properties > Events and add a notification. Choose your event type (ObjectCreated, ObjectRemoved, etc) and point it to the SNS topic.
4. In SNS, create an SMS subscription with your phone number. Confirm when you get the text.

That is it. You will get a message whenever the monitored event fires for that bucket.

S3 Events - Cost

A few things to factor in:

S3 charges for event notifications. As of 2025, it is around $0.50 per million events for standard events. Replication events cost more - roughly $4 per million.

Your destination also matters. SNS charges for notifications sent (about $0.50 per million SMS, $0.06 per million emails). SQS is cheaper - just data transfer and no per-message fees. Lambda charges based on execution time and memory.

Data transfer between regions or out to the internet adds cost too.

For a rough idea: 1 million events per month with SNS email notifications runs you about a dollar total. Not expensive for most use cases, but watch the volume if you are processing high-frequency object creates.

EventBridge or Native S3 Events?

Native S3 events are simple. One bucket, one destination, done. EventBridge gives you more rope - a central event bus, multiple sources and targets, filtering, transformation, and cross-service routing.

Pick native S3 events if:

• You only have one bucket and simple routing needs
• You want the quickest setup

Pick EventBridge if:

• You need to fan out to multiple targets from multiple sources
• You want event filtering and transformation before delivery
• You are already using EventBridge for other services and want a unified interface
• You need advanced routing patterns or partner integrations

The difference in cost is negligible for most small workloads. The difference in flexibility is not.

Wrapping Up

S3 events are useful for tying actions to data changes. They are straightforward to set up, cheap at low volume, and cover most basic event-driven workflows.

If your needs grow beyond simple bucket-to-target routing, EventBridge is worth a look. It adds complexity but also adds control.

That is the lay of the land. Go build something.

If you’re using S3 events to trigger image processing, see AWS Lambda + Pillow for complex image processing for a practical example of Lambda handling S3 upload events to resize and transform images at scale.