Set up a Django App to Respond to S3 Events on AWS Lambda

 I'm going to show you how to set up your Django app to respond to S3 events on AWS Lambda. The tool we're using to get Django running on AWS Lambda is 

. Follow along to see how responding to events works with this setup. ...

When running your Django app on AWS Lambda using Zappa, it's easy to send and receive events from 

Let's configure our Django with Zappa project to detect when new files are uploaded to an S3 bucket.

You'll need a Django project configured with Zappa. You can create a Django project, then follow the guide for 

Once your project is set up properly, log into the AWS console and create an S3 bucket with a unique name. The bucket won't need public access for this tutorial since we'll upload files directly using the AWS console. Once the bucket is ready, click on 'Properties' and record the 

At the root of your project, create a new file called 

. In this file, we'll add the handler function that will accept all our S3 events. When AWS invokes your function, two objects are passed in: the 

 contains metadata about the invocation, function, and execution environment.  

# aws_events.py

import json


def s3_bucket_event(event, context):
    print(
        "Received event: "
        + json.dumps(event, indent=2)
    )

Our event handler code above prints out the 

Finally, we need to tell Zappa to register our event handler function with AWS so that AWS can start sending events.

"events": [
    {
        "function": 
         "YOUR_APP_NAME_HERE
          .aws_events
          .s3_bucket_event",
        "event_source": {
            "arn": 
              "YOUR_S3_BUCKET_ARN_HERE",
            "events": [
                "s3:ObjectCreated:*"
            ]
        }
    }
]

With all the changes saved, go ahead and push these changes to the cloud.

In order to see the event details that our code prints out, let's activate the Zappa console log. You can do this by running:

This gets Zappa to show you what your Django project is printing. Leave it up and running and remember you can exit anytime by pressing 

Head back over to your AWS console and find your S3 bucket page. Under the 

 tab, find the upload button. Go ahead and upload a file. Any file will do, but it's best to send a smaller one for expediency.

After a few seconds, you should see in the terminal window the full event information from S3. It should look something like the following:

[1622565816462] [DEBUG] 
2021-06-01T16:43:36.462Z 21aefbe9-0f48-
438e-b62d-9657be31e99c 
Zappa Event: {'Records': [{
'eventVersion': '2.1', 
'eventSource': 'aws:s3', 'awsRegion': 
'us-east-1', 'eventTime': 
'2021-06-01T16:43:28.948Z', 'eventName':
'ObjectCreated:Put', 'userIdentity': 
{'principalId': 
'AWS:AIDAQ5B2WBSQXTDZ3SBP6'},  
{'s3SchemaVersion': '1.0', 
'configurationId': 
'newline-zappa-course-dev:aws_events
.s3_bucket_event', 
'bucket': 
{'name': 'newline-upload-bucket', 
'ownerIdentity': 
{'principalId': 'A3BGW0C0R9XGAY'}, 
'arn': 
'arn:aws:s3:::newline-upload-bucket'}, 
'object': {'key': 'testfile.jpg', 
'size': 264671, 'eTag': 
'7792fa0fcecf407e15bd79099d8ba88c', 
'sequencer': '0060B663B63D9DD2ED'}}}]}
[1622565816463] Received event: {
[1622565816463] "Records": [
[1622565816463] {
[1622565816463] "eventVersion": 
"2.1",
[1622565816463] "eventSource": 
"aws:s3",
[1622565816463] "awsRegion": 
"us-east-1",
[1622565816463] "eventTime": 
"2021-06-01T16:43:28.948Z",
[1622565816463] "eventName": 
"ObjectCreated:Put",
[1622565816463] "userIdentity": {
[1622565816463] "principalId": 
"AWS:AIDAQ5D2WBSQXTDZ3SBP6"
[1622565816463] },
[1622565816463] "configurationId": 
"newline-zappa-course-dev:
 aws_events.s3_bucket_event",
[1622565816463] "bucket": {
[1622565816463] "name": 
"newline-upload-bucket",
[1622565816463] "ownerIdentity": {
[1622565816463] "principalId": 
"A3DGW0C0R9XGAY"
[1622565816463] },
[1622565816463] "arn": 
"arn:aws:s3:::newline-upload-bucket"
[1622565816463] },
[1622565816463] "object": {
[1622565816463] "key": "testfile.jpg",
[1622565816463] "size": 264671,

A few things to note here. The filename is 

. Of course, your file and bucket will be named differently. Also note the formatting is a little wonky, but still readable.

You can try uploading a few more files. Maybe try two or three at once. You'll see each upload handled by your Django project as independent events.

At this point, we have many options. Maybe your app will create a thumbnail if an image was uploaded. Or scan a document for keywords. Alternatively, your app might send an email to the client that uploaded the file confirming the receipt of the file.

To dive in even more into setting up your Python apps to run serverless on AWS Lambda, check out our latest course,

The newline Guide to Serverless Django with Zappa. 

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