What are Lambda layers, and when would you use them?

0-2 years experience

1. 1You need to add the same third‑party Python library to three Lambda functions. How would you use a Lambda layer to accomplish this?
2. 2If you attach a layer that is 30 MB to a function whose own code is 25 MB, will the function deploy successfully? Why or why not?

2-5 years experience

1. 1During a sprint you notice that a new version of a shared library breaks one of the functions that uses a layer. Walk me through how you would debug and fix the issue.
2. 2We have a microservice that spins up many Lambdas, each needing a large native binary. Explain the trade‑offs of putting that binary in a layer versus bundling it with each function.

5-8 years experience

1. 1Our team wants to standardize a security‑related SDK across dozens of Lambdas in multiple accounts. How would you design a layer strategy that handles versioning, cross‑account access, and minimal cold‑start impact?
2. 2If a layer grows to 45 MB and you start seeing increased cold‑start latency, what steps would you take to investigate and mitigate the performance degradation?

8+ years experience

1. 1We are migrating a legacy monolith to a serverless architecture and want to reuse existing shared libraries via layers. Describe the architectural considerations, including CI/CD pipeline changes, governance, and how you’d avoid layer sprawl over time.
2. 2How would you approach a cross‑team policy for layer publishing that balances rapid iteration with stability, especially when multiple teams depend on the same layer in production?