# Set up a Lambda proxy integration with payload response streaming in API Gateway
You can stream the response of a Lambda function to improve time to first byte (TTFB) performance and send partial responses back to the client as they become available. API Gateway requires you to use the [InvokeWithResponseStream](https://docs.aws.amazon.com/lambda/latest/api/API_InvokeWithResponseStream.html) Lambda API to invoke your Lambda function. API Gateway passes an event object to the Lambda function. The backend Lambda function parses the incoming request data to determine the response that it returns. In order for API Gateway to stream the Lambda output, the Lambda function must output the [format](#response-transfer-mode-lambda-format) required by API Gateway.
## Differences in Lambda proxy integrations between stream and buffered response transfer mode
The following list describes the differences between a Lambda proxy integration and a Lambda proxy integration for response streaming:
+ API Gateway uses the [InvokeWithResponseStream](https://docs.aws.amazon.com/lambda/latest/api/API_InvokeWithResponseStream.html) API to invoke the Lambda proxy integration for response streaming. This results in a different URI, which is the following:
```
arn:aws:apigateway:us-west-1:lambda:path/2021-11-15/functions/arn:aws:lambda:us-west-1:111122223333:function:my-function-name/response-streaming-invocations
```
This ARN uses a different date for the API version and a different service action compared to Lambda proxy integration.
If you use the API Gateway console for response streaming, the console uses the correct URI for you.
+ In a Lambda proxy integration, API Gateway sends the response to client only after it receives the full response from Lambda. In a Lambda proxy integration for response streaming, API Gateway begins the payload stream after it receives the valid metadata and delimiter from Lambda.
+ Lambda proxy integration for response streaming uses the same input format as the proxy integration, but it requires a different output format.
## Lambda proxy integration format for response streaming
When API Gateway invokes a Lambda function with response streaming, the input format is the same as the input format of a Lambda function for proxy integration. For more information, see [Input format of a Lambda function for proxy integration](set-up-lambda-proxy-integrations.md#api-gateway-simple-proxy-for-lambda-input-format).
When Lambda streams a response to API Gateway, the response must adhere to the following format. This format uses a delimiter to separate the metadata JSON and the raw payload. In this case, the payload data is streamed as it is transmitted by your streaming Lambda function:
```
{
"headers": {"headerName": "headerValue", ...},
"multiValueHeaders": { "headerName": ["headerValue", "headerValue2", ...], ... },
"cookies" : ["cookie1", "cookie2"],
"statusCode": httpStatusCode
}PAYLOAD1 | PAYLOAD2 | PAYLOAD3
```
In the output:
+ The `headers`, `multiValueHeaders`, `cookies`, and `statusCode` keys can be unspecified if no extra response headers are to be returned.
+ The `headers` key can only contain single-value headers.
+ The output expects the headers to contain either `Transfer-Encoding: chunked` or `Content-length: number`. If your function doesn't return either of these headers, API Gateway appends `Transfer-Encoding: chunked` to the response header.
+ The `multiValueHeaders` key can contain multi-value headers as well as single-value headers. You can use the `multiValueHeaders` key to specify all of your extra headers, including any single-value ones.
+ If you specify values for both `headers` and `multiValueHeaders`, API Gateway merges them into a single list. If the same key-value pair is specified in both, only the values from `multiValueHeaders` will appear in the merged list.
+ The metadata must be valid JSON. Only `headers`, `multiValueHeaders`, `cookies` and the `statusCode` keys are supported.
+ You must provide a delimiter after the metadata JSON. The delimiter must be 8 null bytes and it must appear within the first 16KB of stream data.
+ API Gateway doesn't require a specific format for the method response payload.
If you're using a function URL to stream your Lambda function, you must modify the input and the output of your Lambda function to satisfy these requirements.
If your Lambda function output doesn't adhere to the requirements of this format, API Gateway might still invoke your Lambda function. The following table shows the combinations of API integration request settings and Lambda function code that is supported by API Gateway. This includes supported combinations for response transfer mode of buffered.
| Response transfer mode | Function code adheres to the required format | Lambda invoke API | Supported by API Gateway |
| --- | --- | --- | --- |
| Stream | Yes | [InvokeWithResponseStream](https://docs.aws.amazon.com/lambda/latest/api/API_InvokeWithResponseStream.html) | Yes. API Gateway streams your response. |
| Stream | No | [InvokeWithResponseStream](https://docs.aws.amazon.com/lambda/latest/api/API_InvokeWithResponseStream.html) | No. API Gateway invokes your Lambda function and return a 500 error response. |
| Stream | Yes | [Invoke](https://docs.aws.amazon.com/lambda/latest/api/API_Invoke.html) | No. API Gateway doesn't support this integration configuration. |
| Stream | No | [Invoke](https://docs.aws.amazon.com/lambda/latest/api/API_Invoke.html) | No. API Gateway doesn't support this integration configuration. |
| Buffered | Yes | [InvokeWithResponseStream](https://docs.aws.amazon.com/lambda/latest/api/API_InvokeWithResponseStream.html) | No. API Gateway doesn't support this integration configuration. |
| Buffered | No | [InvokeWithResponseStream](https://docs.aws.amazon.com/lambda/latest/api/API_InvokeWithResponseStream.html) | No. API Gateway doesn't support this integration configuration. |
| Buffered | Yes | [Invoke](https://docs.aws.amazon.com/lambda/latest/api/API_Invoke.html) | API Gateway returns the HTTP headers and status code but not the response body. |
| Buffered | No | [Invoke](https://docs.aws.amazon.com/lambda/latest/api/API_Invoke.html) | Yes. This is a Lambda proxy integration. For more information, see [Lambda proxy integration](set-up-lambda-proxy-integrations.md). |
# Configure a Lambda proxy integration with payload response streaming in API Gateway
When you set up response payload streaming, you specify the transfer mode in the integration request of your resource. You configure these settings in the integration request to control how API Gateway behaves before and during the integration response.
## Example Lambda functions for response streaming
Your Lambda function must adhere to the [Lambda proxy integration format for response streaming](response-transfer-mode-lambda.md#response-transfer-mode-lambda-format). We recommend you use one of the three example Lambda functions to test out response streaming. When you create your Lambda function, make sure to do the following:
+ Provide an adequate timeout for your function. We recommend you configure a timeout of at least 1 minute to learn about response streaming. When you create your production resources, make sure your Lambda function timeout covers the full request cycle. For more information, see [Configure Lambda function timeout](https://docs.aws.amazon.com/lambda/latest/dg/configuration-timeout.html).
+ Use the latest Node.js runtime.
+ Use a Region where Lambda response streaming is available.
------
#### [ Using HttpResponseStream.from ]
The following code example streams the JSON metadata objects and payloads back to the client using the `awslambda.HttpResponseStream()` method without using the pipeline method. You don't need to create the delimiter. For more information, see [Writing response streaming-enabled Lambda functions](https://docs.aws.amazon.com/lambda/latest/dg/config-rs-write-functions.html).
```
export const handler = awslambda.streamifyResponse(
async (event, responseStream, context) => {
const httpResponseMetadata = {
"statusCode": 200,
"headers": {
"x-foo": "bar"
},
"multiValueHeaders": {
"x-mv1": ["hello", "world"],
"Set-Cookie": ["c1=blue", "c2=red"]
}
};
responseStream = awslambda.HttpResponseStream.from(responseStream, httpResponseMetadata);
await new Promise(r => setTimeout(r, 1000)); // synthetic delay
responseStream.write("First payload ");
await new Promise(r => setTimeout(r, 1000)); // synthetic delay
responseStream.write("Final payload");
responseStream.end();
});
```
------
#### [ Using the pipeline method ]
Lambda recommends that when you write response streaming-enabled functions, you use the `awslambda.streamifyResponse()` decorator that the native Node.js runtimes provide, and the `pipeline()` method. When you use the pipeline method, you don't need to create the delimiter, Lambda does this for you. For more information, see [Writing response streaming-enabled Lambda functions](https://docs.aws.amazon.com/lambda/latest/dg/config-rs-write-functions.html).
The following code example streams the JSON metadata objects and three payloads back to the client.
```
import { pipeline } from 'node:stream/promises';
import { Readable } from 'node:stream';
export const handler = awslambda.streamifyResponse(
async (event, responseStream, context) => {
const httpResponseMetadata = {
statusCode: 200,
headers: {
"Content-Type": "text/plain",
"X-Custom-Header": "Example-Custom-Header"
}
};
responseStream = awslambda.HttpResponseStream.from(responseStream, httpResponseMetadata);
const dataStream = Readable.from(async function* () {
yield "FIRST payload\n";
await new Promise(r => setTimeout(r, 1000));
yield "SECOND payload\n";
await new Promise(r => setTimeout(r, 1000));
yield "THIRD payload\n";
await new Promise(r => setTimeout(r, 1000));
}());
await pipeline(dataStream, responseStream);
}
);
```
------
#### [ Without using the pipeline method ]
The following code example streams the JSON metadata objects and three payloads back to the client without using the `awslambda.HttpResponseStream()` method. Without the `awslambda.HttpResponseStream()` method, you must include a delimiter of 8 null bytes between the metadata and the payload.
```
export const handler = awslambda.streamifyResponse(async (event, response, ctx) => {
response.write('{"statusCode": 200, "headers": {"hdr-x": "val-x"}}');
response.write("\x00".repeat(8)); // DELIMITER
await new Promise(r => setTimeout(r, 1000));
response.write("FIRST payload");
await new Promise(r => setTimeout(r, 1000));
response.write("SECOND payload");
await new Promise(r => setTimeout(r, 1000));
response.write("FINAL payload");
response.end();
});
```
------
## Create a Lambda proxy integration with payload response streaming
The following procedure shows how to create a Lambda proxy integration with payload response streaming. Use the example Lambda function or create your own.
------
#### [ AWS Management Console ]
**To create a Lambda proxy integration with payload response streaming**
1. Sign in to the API Gateway console at [https://console.aws.amazon.com/apigateway](https://console.aws.amazon.com/apigateway).
1. Choose a REST API.
1. Choose **Create resource**.
1. For **Resource name**, enter **streaming**.
1. Choose **Create resource**.
1. With the **/streaming** resource selected, choose **Create method**.
1. For **Method type**, choose **ANY**.
1. For **Integration type**, choose **Lambda**.
1. Choose **Lambda proxy integration**.
1. For **Response transfer mode**, choose **Stream**.
1. For **Lambda function**, choose the name of your Lambda function.
The API Gateway console automatically uses [InvokeWithResponseStream](https://docs.aws.amazon.com/lambda/latest/api/API_InvokeWithResponseStream.html) API to invoke the Lambda function. You are responsible for writing a response streaming-enabled Lambda function. For an example, see [Example Lambda functions for response streaming](#response-streaming-lambda-example).
1. Choose **Create method**.
After you create your method, deploy your API.
**To deploy your API**
1. Choose **Deploy API**.
1. For **Stage**, select **New stage**.
1. For **Stage name**, enter **prod**.
1. (Optional) For **Description**, enter a description.
1. Choose **Deploy**.
------
#### [ AWS CLI ]
The following procedure shows you how to import a new API with the `responseTransferMode` set to `STREAM`. If you have an existing integration API and want to modify the `responseTransferMode`, see [Update the response transfer mode for a Lambda proxy integration](#response-streaming-lambda-update).
**To create a new API with payload response streaming**
1. Copy the following Open API file, and then save it as `ResponseStreamDemoSwagger.yaml`. In this file, `responseTransferMode` is set to `STREAM`, and the integration URI is set to `arn:aws:apigateway:us-west-1:lambda:path/2021-11-15/functions/arn:aws:lambda:us-west-1:111122223333:function:my-function-name/response-streaming-invocations`.
Replace the function name from `my-function` with a streaming-enabled function and replace the credentials with an IAM role that has policies allowing the `apigateway` service to invoke Lambda functions.
```
openapi: "3.0.1"
info:
title: "ResponseStreamingDemo"
version: "2025-04-28T17:28:25Z"
servers:
- url: "{basePath}"
variables:
basePath:
default: "prod"
paths:
/lambda:
get:
x-amazon-apigateway-integration:
httpMethod: "POST"
uri: "arn:aws:apigateway:us-west-1:lambda:path/2021-11-15/functions/arn:aws:lambda:us-west-1:111122223333:function:my-function-name/response-streaming-invocations"
type: "aws_proxy"
timeoutInMillis: 90000
responseTransferMode: "STREAM"
credentials: "arn:aws:iam::111122223333:role/apigateway-lambda-role"
```
Instead of supplying an IAM role for credentials, you can use the `add-permission` command for Lambda to add resource-based permissions.
1. Use the following `import-rest-api` command to import your OpenAPI definition:
```
aws apigateway import-rest-api \
--body 'fileb://~/ResponseStreamDemoSwagger.yaml' \
--parameters endpointConfigurationTypes=REGIONAL \
--region us-west-1
```
1. Use the following `create-deployment` command to deploy your new API to a stage:
```
aws apigateway create-deployment \
--rest-api-id a1b2c2 \
--stage-name prod \
--region us-west-1
```
------
### Update the response transfer mode for a Lambda proxy integration
The following procedure shows how to update the response transfer mode for a Lambda proxy integration. When you change the response transfer mode to streaming, update your Lambda function so it adheres to the requirements for response streaming. Use the example Lambda function or create your own.
------
#### [ AWS Management Console ]
**To update the response transfer mode for a Lambda proxy integration**
1. Sign in to the API Gateway console at [https://console.aws.amazon.com/apigateway](https://console.aws.amazon.com/apigateway).
1. Choose a REST API.
1. Choose a method.
1. On the **Integration request** tab, under **Integration request settings**, choose **Edit**.
1. For **Response transfer mode**, choose **Stream**.
1. For **Lambda function**, choose the name of your Lambda function.
1. Choose **Save**.
After you update your method, deploy your API.
**To deploy your API**
1. Choose **Deploy API**.
1. For **Stage**, select **New stage**.
1. For **Stage name**, enter **prod**.
1. (Optional) For **Description**, enter a description.
1. Choose **Deploy**.
------
#### [ AWS CLI ]
1. Update your Lambda function to be streaming-enabled.
1. Use the following AWS CLI command to update the integration URI and response transfer mode of your integration:
```
aws apigateway update-integration \
--rest-api-id a1b2c3 \
--resource-id aaa111 \
--http-method ANY \
--patch-operations "[{\"op\":\"replace\",\"path\":\"/uri\",\"value\":\"arn:aws:apigateway:us-west-1:lambda:path/2021-11-15/functions/arn:aws:lambda:us-west-1:111122223333:function:my-function-name/response-streaming-invocations\"}, {\"op\":\"replace\",\"path\":\"/responseTransferMode\",\"value\":\"STREAM\"}]" \
--region us-west-1
```
1. Redeploy your API for the changes to take effect.
------