Amaozn API Gateway の Lambda プロキシ統合を使用している場合に、Lambda 関数のスロットリング時にクライアントにどのようなエラーレスポンスが返るのか検証してみた

import serverlessExpress from "@codegenie/serverless-express";
import cors from "cors";
import express, { Request, Response } from "express";

const app = express();
app.use(cors());
app.use(express.json());

app.get("/companies", (_: Request, res: Response): void => {
  // 同時実行数上限を超過しやすいように2秒待機してからレスポンスを返す
  setTimeout(() => {
    res.status(200).send({ message: "Hello, world!" });
  }, 2000);
});

export const handler = serverlessExpress({ app });

import * as cdk from "aws-cdk-lib";
import * as apigateway from "aws-cdk-lib/aws-apigateway";
import * as lambda_nodejs from "aws-cdk-lib/aws-lambda-nodejs";
import { Construct } from "constructs";

export class MainStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props: cdk.StackProps) {
    super(scope, id, props);

    /**
     * Lambda Function
     */
    const handler = new lambda_nodejs.NodejsFunction(this, "Handler", {
      entry: "src/rest-api-router.ts",
      reservedConcurrentExecutions: 1, // 同時実行数を1に制限してスロットリングを発生しやすくする
    });

    /**
     * API Gateway REST API
     */
    new apigateway.LambdaRestApi(this, "RestApi", {
      handler,
      deployOptions: {
        //実行ログの設定
        dataTraceEnabled: true,
        loggingLevel: apigateway.MethodLoggingLevel.INFO,
        // アクセスログの設定
        accessLogDestination: new apigateway.LogGroupLogDestination(
          new cdk.aws_logs.LogGroup(this, "AccessLogGroup", {
            logGroupName: "/aws/api/RestApi",
            removalPolicy: cdk.RemovalPolicy.DESTROY,
          })
        ),
      },
    });
  }
}

# 1回目のリクエスト
$ curl -s -w "\nステータスコード: %{http_code}\n" https://w0m2k255f1.execute-api.ap-northeast-1.amazonaws.com/prod/companies
{"message":"Hello, world!"}
ステータスコード: 200

# 2回目のリクエスト。1回目のリクエスト開始の直後に実行
$ curl -s -w "\nステータスコード: %{http_code}\n" https://w0m2k255f1.execute-api.ap-northeast-1.amazonaws.com/prod/companies
{"message": "Internal server error"}
ステータスコード: 500

# 1回目のリクエスト
XXX.XXX.XXX.XXX - - [13/May/2025:14:08:42 +0000] "GET /{proxy+} HTTP/1.1" 200 27 fec49cae-b462-4c53-947a-ee0ad2de5966

# 2回目のリクエスト
XXX.XXX.XXX.XXX - - [13/May/2025:14:08:42 +0000] "GET /{proxy+} HTTP/1.1" 500 36 be1bad04-3f12-4185-b90f-d4f84c5d029a

# 1回目のリクエスト
(47d9fbd0-426d-4760-b40d-2c75a922d0ee) Received response. Status: 200, Integration latency: 2165 ms
{
    "statusCode": 200,
    "body": "{\"message\":\"Hello, world!\"}",
    "multiValueHeaders": {
        "x-powered-by": [
            "Express"
        ],
        "access-control-allow-origin": [
            "*"
        ],
        "content-type": [
            "application/json; charset=utf-8"
        ],
        "content-length": [
            "27"
        ],
        "etag": [
            "W/\"1b-tDnArHZ232y12bSoTiMc+/cz4as\""
        ]
    },
    "isBase64Encoded": false
}

# 2回目のリクエスト
(db85798a-4d3d-4050-99c3-d7b0d9e03a99) Received response. Status: 429, Integration latency: 10 ms
(db85798a-4d3d-4050-99c3-d7b0d9e03a99) Endpoint response body before transformations:
{
    "Reason": "ReservedFunctionConcurrentInvocationLimitExceeded",
    "Type": "User",
    "message": "Rate Exceeded."
}