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1What is concurrency in AWS Lambda?
2What is provisioned concurrency, and when should you use it?
3What are Lambda extensions, and how are they useful?
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02 / 03

What is provisioned concurrency, and when should you use it?

Provisioned Concurrency in AWS Lambda

Provisioned Concurrency in AWS Lambda is a feature that keeps a pre-defined number of Lambda instances initialized and ready to respond immediately. Unlike standard Lambda invocations where a cold start may occur, provisioned concurrency eliminates cold starts by always keeping the environment warm and pre-initialized. This is especially useful for latency-sensitive applications where response time is critical.

When to Use Provisioned Concurrency
  1. 1

    For APIs or web applications requiring consistently low latency

  2. 2

    During traffic spikes or predictable high-traffic periods

  3. 3

    For scheduled tasks that must start immediately without cold start delays

  4. 4

    In high-performance backend processing where startup time impacts user experience

How It Works
  1. 1

    You define the number of pre-warmed instances for a specific version or alias of your Lambda function

  2. 2

    AWS continuously keeps that number of instances initialized

  3. 3

    Requests are routed to these pre-initialized instances, avoiding cold starts

Set Up Provisioned Concurrency Using AWS CLI
Difficulty: 6/10
Topics: provisioned concurrency, cold start mitigation, cost trade‑offs

Scenario Questions

0-2 years experience
  1. 1

    We have a Lambda that processes user uploads and you notice occasional latency spikes. How would you configure provisioned concurrency to address this?

  2. 2

    If you set provisioned concurrency to 5 for a function but traffic spikes to 20 requests per second, what happens to the extra requests?

2-5 years experience
  1. 1

    During a recent release you enabled provisioned concurrency for a payment‑processing Lambda, but you saw higher costs without noticeable latency improvement. What could be causing this and how would you troubleshoot?

  2. 2

    Your team wants to use provisioned concurrency for a function with variable traffic throughout the day. How would you decide the right concurrency level and what AWS features could help automate adjustments?

5-8 years experience
  1. 1

    Design a strategy for a high‑traffic API Gateway backed by Lambda where you need sub‑second cold‑start latency for the 99th percentile. Include provisioned concurrency, scaling policies, and cost considerations.

  2. 2

    Explain how you would handle a scenario where a provisioned concurrency limit is reached across multiple functions in the same account, and what architectural changes could mitigate the bottleneck.

8+ years experience
  1. 1

    Your organization is migrating a monolithic service to a serverless architecture using many Lambdas. How would you evaluate the use of provisioned concurrency at scale, considering cross‑team SLAs, budgeting, and operational overhead?

  2. 2

    Discuss the long‑term maintenance implications of relying on provisioned concurrency for latency guarantees, especially when multiple teams share the same AWS account and need to coordinate limits and monitoring.

Follow-up Questions

  • ❓How would you monitor whether provisioned concurrency is delivering the expected latency improvements?
  • ❓What metrics would trigger you to increase or decrease the provisioned concurrency setting?
  • ❓If provisioned concurrency capacity is exhausted, what fallback behavior does Lambda exhibit?