CDK Construct to find pre-bundled Lambda function - heavily inspired by CDK lambda-nodejs package

nx-bundled-lambda-function.ts

import * as lambda from 'aws-cdk-lib/aws-lambda';
import type { CallSite } from 'aws-cdk-lib/aws-lambda-nodejs/lib/util';
import { Construct } from 'constructs';
import fs from 'fs';
import path from 'path';
import process from 'process';

export interface BundledLambdaFunctionProps extends lambda.FunctionOptions {
  /**
   * The name of the exported handler in the entry file.
   *
   * The handler is prefixed with `index.` unless the specified handler value contains a `.`,
   * in which case it is used as-is.
   *
   * @default handler
   */
  readonly handler?: string;

  /**
   * The runtime environment. Only runtimes of the Node.js family are
   * supported.
   *
   * @default Runtime.NODEJS_18_X
   */
  readonly runtime?: lambda.Runtime;
}

/**
 * Inspired to CDK's lambda-nodejs but for pre-bundled code.
 *
 * @see https://github.com/aws/aws-cdk/blob/v2.70.0/packages/@aws-cdk/aws-lambda-nodejs/lib/function.ts
 */
export class BundledLambdaFunction extends lambda.Function {
  constructor(scope: Construct, id: string, props: BundledLambdaFunctionProps) {
    if (props.runtime && props.runtime.family !== lambda.RuntimeFamily.NODEJS) {
      throw new Error('Only `NODEJS` runtimes are supported.');
    }

    const entry = path.resolve(findEntry(id));
    const runtime = props.runtime ?? lambda.Runtime.NODEJS_18_X;
    const handler = props.handler ?? 'index.handler';

    const code = lambda.Code.fromAsset(entry);

    super(scope, id, {
      ...props,
      runtime,
      code,
      handler,
    });
  }
}

/**
 * Searches for pre-bundled handler file
 */
function findEntry(id: string): string {
  // CDK is launcehd from here - the monorepo root
  const rootDir = process.cwd();

  // The file where the Lambda Construct was created from
  const definingFile = path.parse(findDefiningFile());

  const relativeDirectory = path.relative(rootDir, definingFile.dir);

  // Should be the path to the actual Lambda directory, bundled
  const bundledLambdaDirectory = path.join(
    rootDir,
    'dist',
    'lambda',
    relativeDirectory,
    `${definingFile.name}.${id}`,
  );

  if (!fs.existsSync(bundledLambdaDirectory)) {
    throw new Error(`Cannot find handler directory ${bundledLambdaDirectory}`);
  }

  return bundledLambdaDirectory;
}

/**
 * Finds the name of the file where the `BundledLambdaFunction` is defined
 */
function findDefiningFile(): string {
  let definingIndex;
  const sites = callsites();
  for (const [index, site] of sites.entries()) {
    if (site.getFunctionName() === 'BundledLambdaFunction') {
      // The next site is the site where the BundledLambdaFunction was created
      definingIndex = index + 1;
      break;
    }
  }

  if (!definingIndex || !sites[definingIndex]) {
    throw new Error('Cannot find defining file.');
  }

  return sites[definingIndex].getFileName();
}

function callsites(): CallSite[] {
  const _prepareStackTrace = Error.prepareStackTrace;
  Error.prepareStackTrace = (_, stack) => stack;
  const stack = new Error().stack?.slice(1);
  Error.prepareStackTrace = _prepareStackTrace;
  return stack as unknown as CallSite[];
}

project.json

{
  "name": "core-cloud",
  "$schema": "../../../node_modules/nx/schemas/project-schema.json",
  "sourceRoot": "libs/core/cloud/src",
  "projectType": "library",
  "targets": {
    "lambda": {
      "executor": "@nrwl/esbuild:esbuild",
      "outputs": ["{options.outputPath}"],
      "options": {
        "main": "libs/core/cloud/src/index.ts",
        "tsConfig": "libs/core/cloud/tsconfig.lib.json",
        "outputPath": "dist/lambda/libs/core/cloud/src",
        "skipTypeCheck": true,
        "minify": true,
        "sourcemap": true,
        "bundle": true,
        "target": "node18",
        "format": ["cjs"],
        "esbuildOptions": {
          "outExtension": {
            ".js": ".js"
          }
        },
        "additionalEntryPoints": [
          "libs/core/cloud/src/lib/cloud-front.set-cookies.fn/index.ts",
          "libs/core/cloud/src/lib/cloud-front.signing-key-rotation.fn/index.ts",
          "libs/core/cloud/src/lib/data-neo4j.invoke.fn/index.ts",
          "libs/core/cloud/src/lib/identity-management.custom-message.fn/index.ts",
          "libs/core/cloud/src/lib/identity-management.post-confirmation.fn/index.ts",
          "libs/core/cloud/src/lib/identity-management.pre-sign-up.fn/index.ts"

        ]
      }
    }
  },
  "tags": []
}