Lambda concurrency is how many function instances run at the same time. The exam tests how you control it — to protect downstream systems or to eliminate cold-start latency.
Reserved vs provisioned concurrency
Reserved concurrency caps how many instances a function can use (protecting a downstream database from being overwhelmed, and guaranteeing capacity for that function). Provisioned concurrency keeps a set number of instances pre-warmed to remove cold-start latency for latency-sensitive apps. Cold starts hurting a critical API? Provisioned concurrency.
Test yourself
A latency-sensitive API on Lambda suffers from cold-start delays during traffic spikes. What eliminates the cold starts?
- Reserved concurrency
- Provisioned concurrency
- A larger memory setting only
- Increasing the timeout
👉 Click to reveal the answer & explanation
Correct answer: B. Provisioned concurrency keeps instances pre-initialized so there’s no cold-start delay. Reserved concurrency (A) caps concurrency but doesn’t pre-warm; more memory (C) speeds execution slightly but not cold starts; a longer timeout (D) is unrelated.
Related topics
AWS Lambda · API Gateway · Lambda Layers
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