Guidance needed for configuring Next.js 15 streaming with Fastly CDN

[adardesign]

Summary

We are adopting Next.js 15 to leverage its server-side streaming capabilities with React Suspense. While streaming works perfectly in our local development environment, we are encountering issues when deploying our application behind Fastly CDN.

The Problem

When a page with Suspense boundaries is requested through Fastly, the response appears to be fully buffered. Instead of the initial shell being sent immediately followed by streamed chunks, the browser only receives the complete HTML document after the slowest data fetch has resolved on the server. This behavior negates the primary user experience benefit of streaming.

Expected Behavior

We expect Fastly to act as a pass-through for the streamed response from the Next.js server. The initial HTML shell should be delivered to the client instantly, and subsequent chunks generated by resolved Suspense boundaries should be sent as they become available, without being buffered by the CDN.

Our Setup

• Next.js Version: 15.x.x (latest)
• Environment: Self-hosted Node.js server
• CDN: Fastly

What We've Tried

1. Enabling Streaming in Fastly VCL: We have configured set beresp.do_stream = true; within vcl_fetch for responses from our Next.js origin.
2. Header Inspection: We have confirmed that the Next.js server is sending Transfer-Encoding: chunked.
3. Disabling Gzip: We have experimented with disabling gzip compression at the CDN layer to rule out buffering related to that, but the issue persists.

Request for Guidance

Could the team provide official documentation or guidance on the recommended configuration for using Next.js streaming with a streaming-capable CDN like Fastly?

Specifically, we are looking for answers to the following:

• Is there a reference Fastly VCL configuration that is known to work correctly with Next.js streaming?
• Are there specific HTTP headers or other response properties that Next.js relies on for streaming which require special handling or pass-through rules at the CDN level?
• Are there any known incompatibilities or required settings we should be aware of?

Any insights or examples would be immensely helpful for us and likely for other users in the community deploying Next.js in similar enterprise environments.

Thank you for your time and for building a great framework.

Additional information

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Example

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