Lambda throttling occurs when the number of concurrent executions exceeds the available concurrency. This can happen due to account-level concurrency limits, function-level reserved concurrency limits, or sudden traffic spikes.
The most operationally efficient ways to reduce throttling are to increase available concurrency:
Option C: Increasing the function’s reserved concurrency can reduce throttling when the function is being constrained by a too-low reserved concurrency value. Reserved concurrency guarantees a fixed amount of concurrency for the function (and also caps it). If the cap is currently too low, raising it allows more parallel executions and reduces throttles.
Option E: If throttling is due to the account concurrency quota being reached (or burst scaling limits in some patterns), the correct fix is to request a service quota increase. This increases the total available concurrency capacity for the account (and/or specific dimensions), allowing more simultaneous executions across functions.
Why the others are not correct:
A (migrate to EKS) is high effort and not operationally efficient for solving Lambda throttling.
B (maximum age of events) applies to asynchronous event retries/queues; it does not reduce throttling—it only changes how long events remain eligible for processing.
D is irrelevant: adding lambda:GetFunctionConcurrency to the execution role only allows reading settings and does not change throttling behavior.
Therefore, the best operational fixes are to increase reserved concurrency and request a concurrency quota increase.
