🃏 AWS Lambda Flashcards

Q: What is the maximum Lambda function timeout?

A: 15 minutes (900 seconds). For longer tasks, use Step Functions, ECS, or EC2.

Q: What is the difference between reserved and provisioned concurrency?

A: Reserved concurrency guarantees a pool of concurrent executions (limits and reserves). Provisioned concurrency pre-warms environments to eliminate cold starts.

Q: How does Lambda handle async invocation failures?

A: Lambda retries twice with delays. After retries, sends to a dead-letter queue (SQS/SNS) or an on-failure destination.

Q: What is a Lambda layer?

A: A ZIP archive with libraries, runtimes, or config shared across functions. Max 5 layers per function. Total unzipped size ≤ 250 MB.

Q: What is the difference between a version and an alias?

A: A version is an immutable snapshot of code + config. An alias is a named pointer to a version and supports traffic shifting for deployments.

Q: How does event source mapping work?

A: Lambda polls the source (SQS, Kinesis, DynamoDB Streams), fetches records in batches, and invokes the function synchronously.

Q: What is Lambda's maximum deployment package size?

A: 50 MB zipped, 250 MB unzipped (including layers). For larger packages, use container images up to 10 GB.

Q: What causes Lambda cold starts?

A: First invocation or scaling up creates new execution environments. Runtime init, dependency loading, and handler init contribute to latency.

Q: How do you pass secrets to Lambda?

A: Use environment variables encrypted with KMS, or retrieve from Secrets Manager / Parameter Store at runtime. Cache secrets outside the handler.

Q: What is the Lambda execution environment lifecycle?

A: INIT (extensions, runtime, handler init) → INVOKE (handler runs) → SHUTDOWN (cleanup). Environments are reused for subsequent invocations.