Lambda Function URL Throttling

Question

Working on a product that relies on sending off a batch of 10-100 calls to lambda. I want these requests to be as concurrent as possible. I'm noticing that after ~5 calls I start to see throttling on the requests.. No 429s, but they progressively take longer & longer to actually hit the lambda. I have tried enabling provisioned concurrency @ 20 just to see if that changed things, but nada. Is throttling expected behavior for Function URLs? I can certainly switch to an ALB or API gateway (and will eventually anyway), but I want to ensure it's not something I'm missing around Lambda config.

Image below illustrates the effect. Green bar is how long the actual handler takes to process and seems to be ~consistent across calls, and the orange bar is how long the total requests takes client side. Enter image description here

Thanks!

Image below illustrates the effect. Green bar is how long the actual handler takes to process and seems to be ~consistent across calls, and the orange bar is how long the total requests takes client side.
![Enter image description here](/media/postImages/original/IMQgveH0YISMakV4E0JHzi5w)

Thanks!

Answer

It is important to understand the concurrency in Lambda. Below are some of the key points:-
Concurrency is the number of in-flight requests your AWS Lambda function is handling at the same time. For each concurrent request, Lambda provisions a separate instance of your execution environment. 
As your functions receive more requests, Lambda automatically handles scaling the number of execution environments until you reach your account's concurrency limit. 
By default, Lambda provides your account with a total concurrency limit of 1,000 across all functions in a region.
The below link provides give a good understanding and visualizing of concurrency and also talks about a formula which can used to the concurrency:-
https://docs.aws.amazon.com/lambda/latest/dg/lambda-concurrency.html

Lambda Function URL Throttling

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