Feature request: make cold start aware of Provisioned Concurrency

[leandrodamascena]

Use case

Original issue: aws-powertools/powertools-lambda-typescript#3723

When using Provisioned Concurrency (PC) in AWS Lambda, the service initializes and keeps active a number of execution environments so that a portion of the requests can be served by these already-warm environments.

As a Powertools for AWS customer using PC, I'd like the cold start metric, log key, and tracer annotation to correctly reflect whether a request is a cold start or not - which is not currently the case.

Solution/User Experience

Currently Logger, Metrics, and Tracer are not aware of Provisioned Concurrency (PC) because the state required to report cold starts in all of them is maintained internally and is dependent on the amount of requests seen by the utility.

Lambda provides an environment variable AWS_LAMBDA_INITIALIZATION_TYPE that can have three values in the Python runtime: provisioned-concurrency, snap-start or on-demand.

We could use this value to tweak our cold start detection logic to report a non-cold start (aka warm start) whenever PC is enabled.

This should not require any code changes from customers besides upgrading the packages to the latest version.

Alternative solutions

Acknowledgment

• This feature request meets Powertools for AWS Lambda (Python) Tenets
• Should this be considered in other Powertools for AWS Lambda languages? i.e. Java, TypeScript, and .NET