Lambda environments may be reused, but applications cannot rely on one environment persisting forever. Initialize reusable clients without storing request-specific state globally.
Before you start
You should understand regions, identity permissions and the responsibilities of the AWS service being discussed. Sketch request flow and failure boundaries before choosing configuration. Work through these scenarios as designs; provisioning real resources can introduce charges and requires an account-specific permissions and capacity plan.
The practical goal is to reason through this situation: A module-level client can be reused while each invocation retains its own event data. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Separate reusable initialization
A module-level client can be reused across invocations.
Step 2: Keep request state local
User-specific event data should belong to the invocation.
Step 3: Expect environment replacement
Caches and temporary state cannot be the only durable source.
Worked scenario
A module-level client can be reused while each invocation retains its own event data.
Warm invocation A stores user A in a global variable. Invocation B can inherit that value if initialization assumes a fresh environment. Reuse a connection client deliberately, but pass each invocation’s user through local operation parameters. A cold environment must also operate correctly without the previous cache.
Common mistake
A global mutable user value can contaminate later warm invocations.
Verify the behavior
Test warm sequential invocations with different users and a fresh environment.
Interview exercise
Cache configuration safely.
Answer and reasoning
Keep cached data bounded and refreshable, distinguishing immutable initialization from per-request state.
Continue learning
Compare the scenario with the AWS interview questions and test your understanding with the AWS MCQs. For terminology and implementation details, consult the reference material.