Lambda one container per invocation vs ECS thousands of invitations per container?

Is it correct that AWS Lambda will execute only one request on each container at a time? Concurrency allocates separate containers for each request?

An single ECS container can process hundreds or thousands of concurrent requests though.

Why can't a single Lambda container process multiple invocations at once? Or am I misunderstanding?

That's correct. Lambda containers can only process one request at a time. A container can be reused for another request, but only after the current request is done. Both Fargate and Lambda use Firecracker internally, but Lambda is optimized for short term containers that can be provisioned faster.

From the documentation:
> 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. To support your specific account needs, you can request a quota increase and configure function-level concurrency controls so that your critical functions don't experience throttling.

> When Lambda finishes processing the first request, this execution environment can then process additional requests for the same function. For subsequent requests, Lambda doesn't need to re-initialize the environment.