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[conico974]

All these changes only apply to Next 15+

Adds patches to the Next.js codebase to remove unused imports at runtime, improving cold start times. Early tests indicate a performance gain of 120-200 ms without any additional code changes.

Disables the default preloading of routes at startup (which was done in the background). Now by default, only the necessary routes are lazily loaded as needed.
Introduces a new configuration setting to control when routes are preloaded. The available options are:

• none : No preloading, default option
• withWaitUntil: Preload using platform provided waitUntil - Will only occur on the first request
• onWarmerEvent : Preload on warmer events - Need to be done by the wrapper itself, only aws-lambda-streaming does it for now.
• onStart: Preload at startup - Be aware this is a blocking operation

[changeset-bot]

🦋 Changeset detected

Latest commit: 5b6d8d8

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@opennextjs/aws	Patch
app-pages-router	Patch
app-router	Patch

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commit: 5b6d8d8

[martinezdylan]

Would love to see if we could get this one in - hoping to use onWarmerEvent to keep routes preloaded on the warm instances. When we're using available warm option on NextJS (ref. https://sst.dev/docs/component/aws/nextjs/#warm) the instance is technically up but routes aren't loaded - this causes us to still experience cold-ish starts despite the warmer.

cc. @nguyendon for vis

[conico974]

@martinezdylan onWarmerEvent won't work for sst without some change there because sst intercept the warmer event and does it's own thing.
It should work if you use onStart

[martinezdylan]

I guess I'm confused, the PR description mentions this should technically be happening now by default? Wouldn't using onStart make no difference?

What we're experiencing suggests even with warm set to 20, we still are having to load / compile the routes when we first hit the endpoint.

[conico974]

Because as said in the PR description, route preloading at the moment are done in the background, but warmer event return immediately, so the route are not preloaded, only NextServer itself.

The onStart from this PR is blocking, which means that it will not return before having done the preloading, but this would be for everything, not just the warmer event, real cold start would likely be slower (How much will depend on your app and deps)

Ideally you'd only use onWarmerEvent but this means that some change has to be done in sst itself

[vicb]

Great PR!

My comments resolve around adding more documentation.

[vicb]

Suggest:

• Add the default behavior of Next is disabled
• Add some guidelines to pick a value

[conico974]

There is no general guidelines really, it depends so much on the deployed app that everyone should do their own testing. I'll add a comment about that

[vicb]

a couple nits but LGTM

[sommeeeer]

This PR is so good!