I am by no means an expert and am reporting what watching the time differences between Lambda reporting and our network calls shows.
Edit: this is by no means a deal breaker or anything. Just something that shocked me when I first noticed it.
I haven't tried with a NAT Gateway.
This is what I know.
If the response is small, the request duration is small.
Cloudfront > Gateway > Lambda > RDS (PostgreSQL)
Response:
1k | 20ms-60ms
10k | 50ms-90ms
100k | 150ms-200ms
350k | 200ms-450ms
That's a rough gauge of what I've experienced.
I think the throughput on the gateway is the bottleneck.
Test #1 Lambda run time (140 ms) Total waiting time (354ms) Total time (358ms)
Test #2 Lambda run time (300 ms) Total waiting time (490ms) Total time (567ms)
Test #3 Lambda run time (139 ms) Total waiting time (479ms) Total time (485ms)
This is for a 20kb payload single request.
Stack: Custom Domain -> Cloudfront -> API Gateway -> VPC -> Lambda -> NAT Gateway -> ElasticSearch
I am not sure what happened, but I had to move a couple of functions inside the VPC and our response times have remained the same.