AWS Lambda – Reserved vs. Provisioned Concurrency

Reserved Concurrency

• Sets a fixed maximum number of concurrent executions for a function.

• Guarantees availability of those executions for that function only.

• Prevents other functions from consuming the reserved capacity.

• Useful for isolating workloads or protecting critical functions from throttling caused by unrelated traffic spikes.

Provisioned Concurrency

• Keeps pre-initialized execution environments ready to handle requests immediately.

• Eliminates cold start latency for all invocations.

• Can be scaled automatically using Application Auto Scaling with schedules or utilization-based triggers.