Provisioned Concurrency in AWS Lambda: What It Is and How It Works

AWS Lambda provisioned concurrency keeps a set number of function instances ready to respond instantly, avoiding startup delays. It ensures your Lambda functions run fast and consistently by pre-warming them before requests arrive.

How It Works

Imagine you run a coffee shop and want to serve customers quickly. If you have to prepare each coffee only after the customer orders, they wait longer. But if you prepare some coffees in advance, customers get served instantly. Provisioned concurrency works like that for AWS Lambda functions.

Normally, when a Lambda function is called after some idle time, AWS needs to start a new instance, causing a delay called a "cold start." Provisioned concurrency keeps a set number of Lambda instances always ready, so when a request comes, it is handled immediately without waiting.

This helps applications that need fast and predictable response times, like web apps or APIs, by reducing the delay caused by cold starts.

Example

This example shows how to configure provisioned concurrency for an AWS Lambda function using AWS CLI. It sets 5 instances always ready to serve requests.

bash

aws lambda put-provisioned-concurrency-config --function-name my-function --qualifier 1 --provisioned-concurrent-executions 5

Output

{
    "RequestedProvisionedConcurrentExecutions": 5,
    "AvailableProvisionedConcurrentExecutions": 5,
    "AllocatedProvisionedConcurrentExecutions": 5,
    "Status": "READY",
    "StatusReason": "Provisioned concurrency is ready"
}

When to Use

Use provisioned concurrency when your Lambda function needs to respond quickly and consistently, especially for user-facing applications. It is helpful when cold start delays can hurt user experience or cause timeouts.

Common use cases include:

• APIs that require low latency
• Web applications with unpredictable traffic spikes
• Real-time data processing where delays are costly
• Functions triggered by scheduled events needing immediate execution

Keep in mind that provisioned concurrency costs more because AWS keeps instances ready even if they are not used.

Key Points

• Provisioned concurrency pre-warms Lambda instances to avoid cold starts.
• It improves performance by reducing response time variability.
• It requires specifying how many instances to keep ready.
• It is best for latency-sensitive or high-traffic applications.
• It incurs additional cost for keeping instances ready.

Key Takeaways

Provisioned concurrency keeps Lambda instances ready to avoid cold start delays.

It ensures fast and consistent response times for latency-sensitive applications.

You configure how many instances to keep warm based on expected traffic.

It is ideal for APIs, web apps, and real-time processing needing low latency.

Using provisioned concurrency increases cost due to always-on instances.