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Set "x-forwarded-host" as NextServer "host"
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‎.changeset/fresh-wombats-explode.md

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---
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"open-next": patch
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---
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Set "x-forwarded-host" as NextServer "host"

‎README.md

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Create a CloudFront distribution, and dispatch requests to their corresponding handlers (behaviors). The following behaviors are configured:
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| Behavior | Requests | Origin |
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| ----------------- | ------------------- | -------------------------------------------------------------------------------------------------------------------------------------------- |
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| `/_next/static/*` | Hashed static files | S3 bucket |
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| `/_next/image` | Image optimization | image optimization function |
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| `/_next/data/*` | data requests | server function |
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| `/api/*` | API | server function |
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| `/*` | catch all | server function fallback to<br />S3 bucket on 503<br />[see why](#workaround-public-static-files-served-out-by-server-function-aws-specific) |
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| Behavior | Requests | CloudFront Function | Origin |
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| ----------------- | ------------------- | ------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------- |
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| `/_next/static/*` | Hashed static files | - | S3 bucket |
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| `/_next/image` | Image optimization | - | image optimization function |
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| `/_next/data/*` | data requests | set `x-forwarded-host`<br />[see why](#workaround-set-x-forwarded-host-header-aws-specific) | server function |
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| `/api/*` | API | set `x-forwarded-host`<br />[see why](#workaround-set-x-forwarded-host-header-aws-specific) | server function |
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| `/*` | catch all | set `x-forwarded-host`<br />[see why](#workaround-set-x-forwarded-host-header-aws-specific) | server function fallback to<br />S3 bucket on 503<br />[see why](#workaround-public-static-files-served-out-by-server-function-aws-specific) |
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#### Running at edge
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The server function can also run at edge locations by configuring it as Lambda@Edge on Origin Request. The server function can accept both regional request events (API payload version 2.0) and edge request events (CloudFront Origin Request payload). Depending on the shape of the Lambda event object, the function will process the request accordingly.
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To configure the CloudFront distribution:
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| Behavior | Requests | Lambda@Edge | Origin |
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| ----------------- | ------------------- | --------------- | ---------------------------------------------------------------------------------------------------- |
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| `/_next/static/*` | Hashed static files | - | S3 bucket |
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| `/_next/image` | Image optimization | - | image optimization function |
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| `/_next/data/*` | data requests | server function | - |
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| `/api/*` | API | server function | - |
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| `/*` | catch all | server function | S3 bucket<br />[see why](#workaround-public-static-files-served-out-by-server-function-aws-specific) |
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| Behavior | Requests | CloudFront Function | Lambda@Edge | Origin |
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| ----------------- | ------------------- | ------------------------------------------------------------------------------------------- | --------------- | ---------------------------------------------------------------------------------------------------- |
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| `/_next/static/*` | Hashed static files | - | - | S3 bucket |
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| `/_next/image` | Image optimization | - | - | image optimization function |
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| `/_next/data/*` | data requests | set `x-forwarded-host`<br />[see why](#workaround-set-x-forwarded-host-header-aws-specific) | server function | - |
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| `/api/*` | API | set `x-forwarded-host`<br />[see why](#workaround-set-x-forwarded-host-header-aws-specific) | server function | - |
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| `/*` | catch all | set `x-forwarded-host`<br />[see why](#workaround-set-x-forwarded-host-header-aws-specific) | server function | S3 bucket<br />[see why](#workaround-public-static-files-served-out-by-server-function-aws-specific) |
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## Limitations and workarounds
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This means that on cache miss, the request may take slightly longer to process.
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#### WORKAROUND: Set `x-forwarded-host` header (AWS specific)
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When the server function receives a request, the `host` value in the Lambda request header is set to the hostname of the AWS Lambda service instead of the actual frontend hostname. This creates an issue for the server function (middleware, SSR routes, or API routes) when it needs to know the frontend host.
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To work around the issue, a CloudFront function is run on Viewer Request, which sets the frontend hostname as the `x-forwarded-host` header. The function code looks like this:
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```ts
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function handler(event) {
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var request = event.request;
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request.headers["x-forwarded-host"] = request.headers.host;
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return request;
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}
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```
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The server function would then sets the `host` header of the request to the value of the `x-forwarded-host` header when sending the request to the `NextServer`.
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#### WORKAROUND: `NextServer` does not set cache response headers for HTML pages
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As mentioned in the [Server function](#server-lambda-function) section, the server function uses the `NextServer` class from Next.js' build output to handle requests. However, `NextServer` does not seem to set the correct `Cache Control` headers.

‎packages/open-next/src/adapters/server-adapter.ts

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export async function handler(
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event: APIGatewayProxyEventV2 | CloudFrontRequestEvent | APIGatewayProxyEvent
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) {
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debug("handler event", event);
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const internalEvent = convertFrom(event);
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debug("event", event);
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// Parse Lambda event and create Next.js request
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const internalEvent = convertFrom(event);
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// WORKAROUND: Set `x-forwarded-host` header (AWS specific) — https://github.com/serverless-stack/open-next#workaround-set-x-forwarded-host-header-aws-specific
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if (internalEvent.headers["x-forwarded-host"]) {
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internalEvent.headers.host = internalEvent.headers["x-forwarded-host"];
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}
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// WORKAROUND: public/ static files served by the server function (AWS specific) — https://github.com/serverless-stack/open-next#workaround-public-static-files-served-by-the-server-function-aws-specific
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if (publicAssets.files.includes(internalEvent.rawPath)) {

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