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sebstoSebastien Stormacqjbelkins
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Add Multi-Source API Example (#598)
This PR adds a new example demonstrating how to build a Lambda function that handles requests from multiple sources (Application Load Balancer and API Gateway V2) using a single handler. ### What's New **New Example: `Examples/MultiSourceAPI`** A Lambda function that: - Implements `StreamingLambdaHandler` to accept raw `ByteBuffer` events - Dynamically decodes events as either `ALBTargetGroupRequest` or `APIGatewayV2Request` - Returns appropriate responses based on the detected event source - Demonstrates handling multiple AWS service integrations with a single function ### Key Features - **Type-safe event detection**: Uses Swift's `Decodable` to identify the event source at runtime - **Streaming response**: Implements `StreamingLambdaHandler` for efficient response handling - **Complete deployment**: Includes SAM template with both ALB and API Gateway V2 infrastructure - **Production-ready**: Full VPC setup with subnets, security groups, and load balancer configuration ### Files Added - `Examples/MultiSourceAPI/Sources/main.swift` - Lambda handler implementation - `Examples/MultiSourceAPI/Package.swift` - Swift package configuration - `Examples/MultiSourceAPI/template.yaml` - SAM deployment template with ALB and API Gateway V2 - `Examples/MultiSourceAPI/README.md` - Documentation with build, deploy, and test instructions - Updated CI to include the new example ### Use Case This pattern is useful when you want to: - Expose the same Lambda function through multiple AWS services - Reduce code duplication by handling similar requests from different sources - Maintain a single codebase for multi-channel APIs --------- Co-authored-by: Sebastien Stormacq <[email protected]> Co-authored-by: Josh Elkins <[email protected]>
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‎.github/workflows/pull_request.yml‎

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# We pass the list of examples here, but we can't pass an array as argument
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# Instead, we pass a String with a valid JSON array.
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# The workaround is mentioned here https://github.com/orgs/community/discussions/11692
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examples: "[ 'APIGatewayV1', 'APIGatewayV2', 'APIGatewayV2+LambdaAuthorizer', 'BackgroundTasks', 'HelloJSON', 'HelloWorld', 'HelloWorldNoTraits', 'HummingbirdLambda', 'ResourcesPackaging', 'S3EventNotifier', 'S3_AWSSDK', 'S3_Soto', 'Streaming', 'Streaming+Codable', 'ServiceLifecycle+Postgres', 'Testing', 'Tutorial' ]"
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examples: "[ 'APIGatewayV1', 'APIGatewayV2', 'APIGatewayV2+LambdaAuthorizer', 'BackgroundTasks', 'HelloJSON', 'HelloWorld', 'HelloWorldNoTraits', 'HummingbirdLambda', 'MultiSourceAPI', 'ResourcesPackaging', 'S3EventNotifier', 'S3_AWSSDK', 'S3_Soto', 'Streaming', 'Streaming+Codable', 'ServiceLifecycle+Postgres', 'Testing', 'Tutorial' ]"
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archive_plugin_examples: "[ 'HelloWorld', 'ResourcesPackaging' ]"
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archive_plugin_enabled: true
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‎Examples/MultiSourceAPI/.gitignore‎

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.DS_Store
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/.build
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/Packages
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xcuserdata/
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DerivedData/
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.swiftpm/configuration/registries.json
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.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
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.netrc
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Package.resolved
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aws-sam
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samconfig.toml

‎Examples/MultiSourceAPI/Package.swift‎

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// swift-tools-version:6.2
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import PackageDescription
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// needed for CI to test the local version of the library
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import struct Foundation.URL
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let package = Package(
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name: "MultiSourceAPI",
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platforms: [.macOS(.v15)],
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products: [
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.executable(name: "MultiSourceAPI", targets: ["MultiSourceAPI"])
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],
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dependencies: [
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.package(url: "https://github.com/awslabs/swift-aws-lambda-runtime.git", from: "2.0.0"),
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.package(url: "https://github.com/awslabs/swift-aws-lambda-events.git", from: "1.0.0"),
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],
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targets: [
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.executableTarget(
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name: "MultiSourceAPI",
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dependencies: [
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.product(name: "AWSLambdaRuntime", package: "swift-aws-lambda-runtime"),
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.product(name: "AWSLambdaEvents", package: "swift-aws-lambda-events"),
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],
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path: "Sources"
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)
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]
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)
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if let localDepsPath = Context.environment["LAMBDA_USE_LOCAL_DEPS"],
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localDepsPath != "",
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let v = try? URL(fileURLWithPath: localDepsPath).resourceValues(forKeys: [.isDirectoryKey]),
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v.isDirectory == true
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{
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let indexToRemove = package.dependencies.firstIndex { dependency in
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switch dependency.kind {
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case .sourceControl(
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name: _,
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location: "https://github.com/awslabs/swift-aws-lambda-runtime.git",
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requirement: _
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):
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return true
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default:
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return false
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}
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}
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if let indexToRemove {
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package.dependencies.remove(at: indexToRemove)
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}
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print("[INFO] Compiling against swift-aws-lambda-runtime located at \(localDepsPath)")
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package.dependencies += [
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.package(name: "swift-aws-lambda-runtime", path: localDepsPath)
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]
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}

‎Examples/MultiSourceAPI/README.md‎

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# Multi-Source API Example
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This example demonstrates a Lambda function that handles requests from both Application Load Balancer (ALB) and API Gateway V2 by accepting a raw `ByteBuffer` and decoding the appropriate event type.
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## Overview
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The Lambda handler receives events as `ByteBuffer` and attempts to decode them as either:
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- `ALBTargetGroupRequest` - for requests from Application Load Balancer
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- `APIGatewayV2Request` - for requests from API Gateway V2
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Based on the successfully decoded type, it returns an appropriate response.
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## Building
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```bash
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swift package archive --allow-network-connections docker
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```
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## Deploying
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Deploy using SAM:
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```bash
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sam deploy \
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--resolve-s3 \
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--template-file template.yaml \
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--stack-name MultiSourceAPI \
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--capabilities CAPABILITY_IAM
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```
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## Testing
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After deployment, SAM will output two URLs:
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### Test API Gateway V2:
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```bash
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curl https://<api-id>.execute-api.<region>.amazonaws.com/apigw/test
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```
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Expected response:
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```json
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{"source":"APIGatewayV2","path":"/apigw/test"}
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```
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### Test ALB:
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```bash
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curl http://<alb-dns-name>/alb/test
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```
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Expected response:
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```json
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{"source":"ALB","path":"/alb/test"}
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```
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## How It Works
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The handler uses Swift's type-safe decoding to determine the event source:
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1. Receives raw `ByteBuffer` event
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2. Attempts to decode as `ALBTargetGroupRequest`
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3. If that fails, attempts to decode as `APIGatewayV2Request`
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4. Returns appropriate response based on the decoded type
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5. Throws error if neither decoding succeeds
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This pattern is useful when a single Lambda function needs to handle requests from multiple sources.

‎Examples/MultiSourceAPI/Sources/main.swift‎

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//===----------------------------------------------------------------------===//
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//
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// This source file is part of the SwiftAWSLambdaRuntime open source project
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//
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// Copyright SwiftAWSLambdaRuntime project authors
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// Copyright (c) Amazon.com, Inc. or its affiliates.
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// Licensed under Apache License v2.0
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//
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// See LICENSE.txt for license information
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// See CONTRIBUTORS.txt for the list of SwiftAWSLambdaRuntime project authors
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//
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// SPDX-License-Identifier: Apache-2.0
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//
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//===----------------------------------------------------------------------===//
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import AWSLambdaEvents
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import AWSLambdaRuntime
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import NIOCore
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#if canImport(FoundationEssentials)
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import FoundationEssentials
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#else
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import Foundation
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#endif
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struct MultiSourceHandler: StreamingLambdaHandler {
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func handle(
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_ event: ByteBuffer,
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responseWriter: some LambdaResponseStreamWriter,
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context: LambdaContext
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) async throws {
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let decoder = JSONDecoder()
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let data = Data(event.readableBytesView)
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// Try to decode as ALBTargetGroupRequest first
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if let albRequest = try? decoder.decode(ALBTargetGroupRequest.self, from: data) {
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context.logger.info("Received ALB request to path: \(albRequest.path)")
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let response = ALBTargetGroupResponse(
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statusCode: .ok,
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headers: ["Content-Type": "application/json"],
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body: "{\"source\":\"ALB\",\"path\":\"\(albRequest.path)\"}"
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)
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let encoder = JSONEncoder()
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let responseData = try encoder.encode(response)
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try await responseWriter.write(ByteBuffer(bytes: responseData))
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try await responseWriter.finish()
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return
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}
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// Try to decode as APIGatewayV2Request
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if let apiGwRequest = try? decoder.decode(APIGatewayV2Request.self, from: data) {
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context.logger.info("Received API Gateway V2 request to path: \(apiGwRequest.rawPath)")
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let response = APIGatewayV2Response(
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statusCode: .ok,
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headers: ["Content-Type": "application/json"],
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body: "{\"source\":\"APIGatewayV2\",\"path\":\"\(apiGwRequest.rawPath)\"}"
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)
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let encoder = JSONEncoder()
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let responseData = try encoder.encode(response)
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try await responseWriter.write(ByteBuffer(bytes: responseData))
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try await responseWriter.finish()
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return
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}
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// Unknown event type
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context.logger.error("Unable to decode event as ALB or API Gateway V2 request")
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throw LambdaError.invalidEvent
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}
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}
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enum LambdaError: Error {
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case invalidEvent
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}
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let runtime = LambdaRuntime(handler: MultiSourceHandler())
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try await runtime.run()

‎Examples/MultiSourceAPI/template.yaml‎

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AWSTemplateFormatVersion: '2010-09-09'
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Transform: AWS::Serverless-2016-10-31
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Description: Multi-source API Lambda function with ALB and API Gateway V2
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Resources:
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MultiSourceAPIFunction:
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Type: AWS::Serverless::Function
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Properties:
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CodeUri: .build/plugins/AWSLambdaPackager/outputs/AWSLambdaPackager/MultiSourceAPI/MultiSourceAPI.zip
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Handler: provided
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Runtime: provided.al2
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Architectures:
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- arm64
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MemorySize: 256
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Timeout: 30
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Environment:
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Variables:
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LOG_LEVEL: trace
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Events:
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ApiGatewayEvent:
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Type: HttpApi
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Properties:
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Path: /{proxy+}
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Method: ANY
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# VPC for ALB
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VPC:
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Type: AWS::EC2::VPC
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Properties:
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CidrBlock: 10.0.0.0/16
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EnableDnsHostnames: true
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EnableDnsSupport: true
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PublicSubnet1:
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Type: AWS::EC2::Subnet
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Properties:
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VpcId: !Ref VPC
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CidrBlock: 10.0.1.0/24
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AvailabilityZone: !Select [0, !GetAZs '']
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MapPublicIpOnLaunch: true
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PublicSubnet2:
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Type: AWS::EC2::Subnet
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Properties:
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VpcId: !Ref VPC
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CidrBlock: 10.0.2.0/24
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AvailabilityZone: !Select [1, !GetAZs '']
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MapPublicIpOnLaunch: true
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InternetGateway:
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Type: AWS::EC2::InternetGateway
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AttachGateway:
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Type: AWS::EC2::VPCGatewayAttachment
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Properties:
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VpcId: !Ref VPC
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InternetGatewayId: !Ref InternetGateway
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RouteTable:
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Type: AWS::EC2::RouteTable
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Properties:
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VpcId: !Ref VPC
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Route:
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Type: AWS::EC2::Route
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DependsOn: AttachGateway
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Properties:
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RouteTableId: !Ref RouteTable
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DestinationCidrBlock: 0.0.0.0/0
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GatewayId: !Ref InternetGateway
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SubnetRouteTableAssociation1:
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Type: AWS::EC2::SubnetRouteTableAssociation
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Properties:
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SubnetId: !Ref PublicSubnet1
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RouteTableId: !Ref RouteTable
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SubnetRouteTableAssociation2:
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Type: AWS::EC2::SubnetRouteTableAssociation
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Properties:
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SubnetId: !Ref PublicSubnet2
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RouteTableId: !Ref RouteTable
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# Application Load Balancer
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ALBSecurityGroup:
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Type: AWS::EC2::SecurityGroup
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Properties:
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GroupDescription: Security group for ALB
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VpcId: !Ref VPC
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SecurityGroupIngress:
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- IpProtocol: tcp
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FromPort: 80
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ToPort: 80
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CidrIp: 0.0.0.0/0
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ApplicationLoadBalancer:
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Type: AWS::ElasticLoadBalancingV2::LoadBalancer
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Properties:
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Scheme: internet-facing
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Subnets:
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- !Ref PublicSubnet1
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- !Ref PublicSubnet2
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SecurityGroups:
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- !Ref ALBSecurityGroup
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ALBTargetGroup:
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Type: AWS::ElasticLoadBalancingV2::TargetGroup
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DependsOn: ALBLambdaInvokePermission
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Properties:
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TargetType: lambda
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Targets:
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- Id: !GetAtt MultiSourceAPIFunction.Arn
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ALBListener:
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Type: AWS::ElasticLoadBalancingV2::Listener
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Properties:
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LoadBalancerArn: !Ref ApplicationLoadBalancer
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Port: 80
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Protocol: HTTP
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DefaultActions:
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- Type: forward
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TargetGroupArn: !Ref ALBTargetGroup
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ALBLambdaInvokePermission:
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Type: AWS::Lambda::Permission
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Properties:
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FunctionName: !GetAtt MultiSourceAPIFunction.Arn
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Action: lambda:InvokeFunction
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Principal: elasticloadbalancing.amazonaws.com
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Outputs:
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ApiGatewayUrl:
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Description: API Gateway endpoint URL
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Value: !Sub "https://${ServerlessHttpApi}.execute-api.${AWS::Region}.amazonaws.com"
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ALBUrl:
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Description: Application Load Balancer URL
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Value: !Sub "http://${ApplicationLoadBalancer.DNSName}"

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