Adapter Aws Lambda

Use APIGatewayProxyEvent for REST API (v1 payload format) and APIGatewayProxyEventV2 for HTTP API (v2 payload format).

Response streaming with awsLambdaStreamingRequestHandler

/// <reference types="aws-lambda" />
import type { CreateAWSLambdaContextOptions } from '@trpc/server/adapters/aws-lambda';
import { awsLambdaStreamingRequestHandler } from '@trpc/server/adapters/aws-lambda';
import type { APIGatewayProxyEventV2 } from 'aws-lambda';
import { appRouter } from './router';

const createContext = ({
  event,
  context,
}: CreateAWSLambdaContextOptions<APIGatewayProxyEventV2>) => ({});

export const handler = awslambda.streamifyResponse(
  awsLambdaStreamingRequestHandler({
    router: appRouter,
    createContext,
  }),
);

Response streaming is supported for Lambda Function URLs and API Gateway REST APIs (with responseTransferMode: STREAM). The awslambda namespace is provided by the Lambda execution environment.

Streaming async generator procedure

import { initTRPC } from '@trpc/server';

const t = initTRPC.create();

export const appRouter = t.router({
  countdown: t.procedure.query(async function* () {
    for (let i = 10; i >= 0; i--) {
      await new Promise((resolve) => setTimeout(resolve, 500));
      yield i;
    }
  }),
});

Pair with httpBatchStreamLink on the client for streamed responses.

Limiting batch size with maxBatchSize

import { awsLambdaRequestHandler } from '@trpc/server/adapters/aws-lambda';
import { appRouter } from './router';

export const handler = awsLambdaRequestHandler({
  router: appRouter,
  createContext,
  maxBatchSize: 10,
});

Requests batching more than maxBatchSize operations are rejected with a 400 Bad Request error. Set maxItems on your client's httpBatchLink to the same value to avoid exceeding the limit.

Common Mistakes

HIGH Using httpBatchLink with per-procedure API Gateway resources

Wrong:

// API Gateway has a separate resource for each procedure
// e.g., /getUser, /createUser
// Client uses:
import { httpBatchLink } from '@trpc/client';

httpBatchLink({ url: 'https://api.example.com' });
// Batch request to /getUser,createUser → 404

Correct:

import { httpBatchLink, httpLink } from '@trpc/client';

// Option A: Single catch-all resource (e.g., /{proxy+})
httpBatchLink({ url: 'https://api.example.com' });

// Option B: Per-procedure resources with httpLink (no batching)
httpLink({ url: 'https://api.example.com' });

httpBatchLink sends multiple procedure names in the URL path (e.g., getUser,createUser). If API Gateway routes are per-procedure, the combined path does not match any resource and returns 404. Use a single catch-all resource or switch to httpLink.

Source: www/docs/server/adapters/aws-lambda.md

HIGH Forgetting streamifyResponse wrapper for streaming

Wrong:

export const handler = awsLambdaStreamingRequestHandler({
  router: appRouter,
  createContext,
});

Correct:

export const handler = awslambda.streamifyResponse(
  awsLambdaStreamingRequestHandler({
    router: appRouter,
    createContext,
  }),
);

awsLambdaStreamingRequestHandler requires wrapping with awslambda.streamifyResponse() to enable Lambda response streaming. Without it, Lambda treats the handler as a standard buffered response.

Source: www/docs/server/adapters/aws-lambda.md

See Also

• server-setup -- initTRPC.create(), router/procedure definition, context
• adapter-fetch -- alternative for edge/serverless runtimes using Fetch API
• links -- httpBatchLink vs httpLink for API Gateway routing considerations
• AWS Lambda docs: https://docs.aws.amazon.com/lambda/latest/dg/welcome.html