AWS API Gateway Throttling not working as expected - amazon-web-services

Question

I'm trying to enable API Gateway throttling, but it's not working as expected.
I set Default Method Throttling Rate to 1 request per second, and Burst to 1 request.
Then I created a loop in my code to make 10 simultaneous requests to my API endpoint.
for (let i=0; i<10; i++) {
axios.get(url);
}
The expected result would be:
1 successful request
9 throttled requests (HTTP 429 error)
But the actual result was the opposite:
9 successful requests
1 throttled request (HTTP 429 error)
I repeated the process, but making 20 simultaneous request and the result was:
16 successful requests
4 throttled requests (HTTP 429 error)
On CloudWatch logs for this API method, I found different Log streams, each one with only few milliseconds difference.
If I set Rate to 0 requests per second and Burst to 0 request, the throttling works and ALL requests get throttlet. But when I set Rate and Bust to 1 it does not work as expected.
Why is that happening? I need to limit my API to only 1 request per second.

Answer 1

It seems AWS API Gateway throttling is not very precise for small values of rate/burst.
I imagine that there are multiple "instances" of the API Gateway running, and the values of rate and burst are "eventually consistent".
However I did not find any documentation about that.
When I made an initial request and wait 500 milliseconds before making other 99 requests, the results were "less imprecise".
Example:
axios.get(url);
setTimeout(function(){
console.log("After 500 ms");
for (let i=0; i<99; i++) {
axios.get(url);
}
}, 500);
Results:
Once I got 1 success and 99 throttles.
Other time I got 12 success and 88 throttles.
Other time I got 33 success and 67 throttles.
However, it's difficult to have consistent results.

Answer 2

There are two ways to apply limits on API calls:
Account-level throttling
API-level and stage-level throttling
When you need to apply API-level or stage-level throttling, you have to use usage plans:
A usage plan specifies who can access one or more deployed API stages and methods—and also how much and how fast they can access them