LambdaLink
AWS Lambda for Blueprints and C++

Overview

LambdaLink lets you keep game logic that must not run on the client — score validation, rewards, purchases, matchmaking rules, AI calls — in AWS Lambda and call it from Unreal Engine 4.27 and 5.8. Requests run on background worker threads with automatic retries; every result arrives back on the game thread.

• Invoke Lambda: Request / Response, Event (fire and forget) and Dry Run, with optional log tail.
• Invoke Lambda Stream: response-streaming functions delivered piece by piece.
• Invoke Lambda Batch: one function, many payloads, in parallel.
• Send Signed Request: AWS Signature V4 for API Gateway (IAM auth), Lambda function URLs and other AWS endpoints.
• Amazon Cognito identity pools for guests and signed-in players; static keys and the default AWS chain for development and servers.
• JSON helpers to convert payloads to and from Blueprint structs.

Requirements

Installation

1. Install LambdaLink from Fab into your engine, or copy the LambdaLink folder into your project's Plugins folder.
2. Enable LambdaLink in Edit > Plugins and restart the editor.
3. Open Project Settings > Plugins > LambdaLink and set Region and Identity Pool Id.
4. C++ only: add PublicDependencyModuleNames.Add("LambdaLink"); to your Build.cs.

Setting up AWS

1. Create your function in the Lambda console (any runtime). Note its name and region.
2. In Amazon Cognito create an identity pool. Enable guest access if players may call functions before signing in, and add your identity providers (for example a Cognito user pool).
3. Edit the IAM role the pool gives to players (authenticated and/or guest) so it may invoke only your game's functions:

{
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Action": ["lambda:InvokeFunction", "lambda:InvokeWithResponseStream"],
    "Resource": "arn:aws:lambda:us-east-1:123456789012:function:mygame-prod-*"
  }]
}

For API Gateway routes with IAM authorization add execute-api:Invoke on the route ARNs.

Quick start

Blueprint

1. Add Invoke Lambda to an Event Graph. Function Name SubmitScore, Payload {"score": 1200}.
2. From On Success, read Result > Payload or call Get JSON Field with Path rank.
3. From On Failure, print Error > Message; Error > Code says why.
4. To send a struct, convert it with Struct To JSON; read replies into a struct with JSON To Struct.

Streaming

Configure the function for response streaming (Node.js awslambda.streamifyResponse) and call Invoke Lambda Stream. Append each On Chunk text to a widget; On Completed carries the whole payload.

Latent nodes

All latent nodes run in the background, can be stopped with Cancel on their return value and fire exactly one final pin on the game thread.

Functions

Credentials

Signed-in players: for a Cognito user pool call Set Login Token with Provider = Make User Pool Provider Name and Token = the ID token. Other providers use their pool login keys (accounts.google.com, appleid.apple.com, graph.facebook.com).

C++ API

// Build.cs: PublicDependencyModuleNames.Add("LambdaLink");
#include "LambdaLinkLibrary.h"

ULambdaLinkLibrary::InvokeNative(TEXT("SubmitScore"), TEXT("{\"score\":1200}"),
    ELambdaLinkInvocationType::RequestResponse, FString(), false,
    FLambdaLinkNativeDelegate::CreateLambda([](const FLambdaLinkResult& Result, const FLambdaLinkError& Error)
    {
        // runs on the game thread
    }));

The latent node classes (ULambdaLinkInvokeAction and the others) can also be created from C++ through their static factory functions; bind the delegates, then call Activate().

Types

Settings

Project Settings > Plugins > LambdaLink (saved to DefaultGame.ini). Changes apply to the next request.

Troubleshooting

Credits

© 2026 Alpha XP — alphaxp.net · Support: support@alphaxp.net. Includes the AWS SDK for C++ and the AWS Common Runtime (Apache License 2.0). Built and verified for Unreal Engine 4.27 and 5.8.