Different types of events triggered by Amazon CloudFront are as follows:

1. Viewer Request: When an end user or a client program makes an

HTTP/HTTPS request to CloudFront, this event is triggered at the

Edge Location closer to the end user.

2. Viewer Response: When a CloudFront server is ready to respond to

a request, this event is triggered.

3. Origin Request: When CloudFront server does not have the

requested object in its cache, the request is forwarded to Origin

server. At this time this event is triggered.

4. Origin Response: When CloudFront server at an Edge location

receives the response from Origin server, this event is triggered

https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/lambda-cloudfront-trigger-events.html