Static initialization and Provisioned Concurrency

In on-demand Lambda functions, the static initializer is run after a request is received but before the handler is invoked. This results in latency for the requester and contributes to the overall cold start duration. While you can optimize the static initializer as shown in the preceding section, there are times where you may need to perform large amounts of work here, and cannot avoid a long INIT duration.

Provisioned allows you to prepare execution environments before receiving traffic, making it ideal for functions with complex and lengthy INIT code. In this case, the duration of the INIT code does not impact the overall performance of an invocation.

While all Provisioned Concurrency functions start more quickly than the existing on-demand Lambda execution style, this is particularly beneficial for some function profiles. Runtimes like C# and Java have much slower initialization times than Node.js or Python, but faster execution times once initialized. With Provisioned Concurrency turned on, these runtimes benefit from both the consistent low latency of the function’s start-up and the performance during execution.