AWS Lambda - not understanding returned data

I am writing my first Lambda script. It is a very simple HTTP to email gateway. While it is parsing the request and generating the email, I get a 502 error at the front end (via Cloudfront):

> The Lambda function returned an invalid entry in the headers object: Each header entry in the headers object must be an array. We can't connect to the server for this app or website at this time. There might be too much traffic or a configuration error. Try again later, or contact the app or website owner.
If you provide content to customers through CloudFront, you can find steps to troubleshoot and help prevent this error by reviewing the CloudFront documentation.

To create the returned object, I am simply decorating the event object passed to lambda_handler():

def lambda_handler(event, context):
returnAddr=do_clever_stuff(event)
response = {
"headers": { "location": [ { "key": "Location", "value": returnAddr } ] },
"status": 303,
"statusDescription": "See Other"
}
event['Records'][0]['cf']['response']=response
return event

The entire data returned in the Lambda editor / test console is shown below.

I think that my response conforms to the requirements. What am I missing?

{
"Records": [
{
"cf": {
"config": {
"distributionDomainName": "redacted.cloudfront.net",
"distributionId": "EDFDVBD6EXAMPLE",
"eventType": "origin-request",
"requestId": "4TyzHTaYWb1GX1qTfsHhEqV6HUDd_BzoBZnwfnvQc_1oF26ClkoUSEQ=="
},
"request": {
"clientIp": "203.0.113.178",
"headers": {
"x-forwarded-for": [
{
"key": "X-Forwarded-For",
"value": "203.0.113.178"
}
],
"user-agent": [
{
"key": "User-Agent",
"value": "Amazon CloudFront"
}
],
"via": [
{
"key": "Via",
"value": "2.0 2afae0d44e2540f472c0635ab62c232b.cloudfront.net (CloudFront)"
}
],
"host": [
{
"key": "Host",
"value": "example.org"
}
],
"cache-control": [
{
"key": "Cache-Control",
"value": "no-cache"
}
]
},
"method": "POST",
"origin": {
"custom": {
"customHeaders": {},
"domainName": "example.org",
"keepaliveTimeout": 5,
"path": "",
"port": 443,
"protocol": "https",
"readTimeout": 30,
"sslProtocols": [
"TLSv1",
"TLSv1.1",
"TLSv1.2"
]
}
},
"querystring": "",
"uri": "/",
"body": {
"data": "<<redacted>>"
}
},
"response": {
"headers": {
"location": [
{
"key": "Location",
"value": "/"
}
]
},
"status": 303,
"statusDescription": "See Other"
}
}
}
]
}

Update Looking at other examples in the AWS documentation, these are not returning a decorated event object, but rather just the response object, however amending the code above to return response does not change the behaviour.

First, (as you have found) you don't return an updated event object, you should simply return the response object directly.

Second, if changing your code to simply return the response object is still resulting in the same event/response thing coming back, then you forgot to click the "deploy" button in the Lambda console before testing the function again.

The issue turned out to be that clicking "deploy" in the Lambda console does not deploy the script to Lambda@edge.

To make the current code live, I apparently need to switch to the "versions" tab, create a new version, then edit the cloudfront distribution to update the function ARN to that of the new version.

Just to clarify the earlier confusion, lambda_handler() needs to return a response object - not a complete event object.