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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?

Difficulty: 6/10
provisioned concurrency, cold start mitigation, cost trade‑offs

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

Scenario Questions

0-2 years experience

  1. 1We have a Lambda that processes user uploads and you notice occasional latency spikes. How would you configure provisioned concurrency to address this?
  2. 2If 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. 1During 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. 2Your 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. 1Design 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. 2Explain 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. 1Your 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. 2Discuss 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?
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