Class Utility

Utility is a base class that other Powertools for AWS Lambda (TypeScript) utilites can extend to inherit shared logic.

Its main purpose is to encapsulate the cold start heuristic logic. Cold start is a term commonly used to describe the Init phase of a Lambda function. In this phase, Lambda creates or unfreezes an execution environment with the configured resources, downloads the code for the function and all layers, initializes any extensions, initializes the runtime, and then runs the function’s initialization code (the code outside the main handler).

The Init phase happens either during the first invocation, or in advance of function invocations if you have enabled provisioned concurrency.

To learn more about the Lambda execution environment lifecycle, see the Execution environment section of the AWS Lambda documentation.

As a Powertools for AWS Lambda (TypeScript) user you probably won't be using this class directly, in fact if you use other Powertools for AWS utilities the cold start heuristic found here is already used to:

• Add a coldStart key to the structured logs when injecting context information in Logger
• Emit a metric during a cold start function invocation in Metrics
• Annotate the invocation segment with a coldStart key in Tracer

If you want to use this logic in your own utilities, Utility provides two methods:

Utility.getColdStart()

Since the Utility class is instantiated outside of the Lambda handler it will persist across invocations of the same execution environment. This means that if you call getColdStart() multiple times, it will return true during the first invocation, and false afterwards.

import { Utility } from '@aws-lambda-powertools/commons';

const utility = new Utility();

export const handler = async (_event: any, _context: any) => {
  utility.getColdStart();
};
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import { Utility } from '@aws-lambda-powertools/commons';

const utility = new Utility();

export const handler = async (_event: any, _context: any) => {
  if (utility.isColdStart()) {
    // do something, this block is only executed on the first invocation of the function
  } else {
    // do something else, this block gets executed on all subsequent invocations
  }
};
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