Support profiling the startup phase of a Worker

[penalosa]

This PR adds two features (separate changesets):

• Support for the --outfile argument for wrangler deploy, which outputs the exact Worker bundle that Wrangler will upload to the Cloudflare API. This has more information than just --outdir because it bakes in bindings & module types.
• wrangler check startup, which profiles the startup time of a Worker and generates a .cpuprofile file that can be opened in Chrome DevTools/directly in VSCode for further investigation. Additionally, this is automatically generated when Wrangler encounters a startup time error from the API.

---

• Tests
  • TODO (before merge)
  • Tests included
  • Tests not necessary because:
• E2E Tests CI Job required? (Use "e2e" label or ask maintainer to run separately)
  • I don't know
  • Required
  • Not required because:
• Public documentation
  • TODO (before merge)
  • Cloudflare docs PR(s): Add wrangler check startup docs cloudflare-docs#19877
  • Documentation not necessary because:

[changeset-bot]

🦋 Changeset detected

Latest commit: 989f763

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

This PR includes changesets to release 2 packages

Name	Type
wrangler	Minor
@cloudflare/vitest-pool-workers	Patch

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[github-actions]

A wrangler prerelease is available for testing. You can install this latest build in your project with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-wrangler-8026

You can reference the automatically updated head of this PR with:

npm install --save-dev https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/prs/8026/npm-package-wrangler-8026

Or you can use npx with this latest build directly:

npx https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-wrangler-8026 dev path/to/script.js

Additional artifacts:

cloudflare-workers-bindings-extension:

wget https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-workers-bindings-extension-8026 -O ./cloudflare-workers-bindings-extension.0.0.0-vd6e483add.vsix && code --install-extension ./cloudflare-workers-bindings-extension.0.0.0-vd6e483add.vsix

create-cloudflare:

npx https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-create-cloudflare-8026 --no-auto-update

@cloudflare/kv-asset-handler:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-kv-asset-handler-8026

miniflare:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-miniflare-8026

@cloudflare/pages-shared:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-pages-shared-8026

@cloudflare/unenv-preset:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-unenv-preset-8026

@cloudflare/vite-plugin:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-vite-plugin-8026

@cloudflare/vitest-pool-workers:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-vitest-pool-workers-8026

@cloudflare/workers-editor-shared:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-workers-editor-shared-8026

@cloudflare/workers-shared:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-workers-shared-8026

@cloudflare/workflows-shared:

npm install https://prerelease-registry.devprod.cloudflare.dev/workers-sdk/runs/13265276676/npm-package-cloudflare-workflows-shared-8026

Note that these links will no longer work once the GitHub Actions artifact expires.

---

[email protected] includes the following runtime dependencies:

Package	Constraint	Resolved
miniflare	workspace:*	3.20250129.0
workerd	1.20250204.0	1.20250204.0
workerd --version	1.20250204.0	2025-02-04

Please ensure constraints are pinned, and miniflare/workerd minor versions match.

[emily-shen]

Pages build already has an outfile, is this supposed to reuse that...? Can pages deploy fail due to startup time, and should this generate a cpuprofile if that's the case?

[emily-shen]

not blocking, especially since its hidden, but it feels odd this has its own command. Do we anticipate other 'check' commands?

...maybe we should make wrangler deploy --dry-run a check command?? (come to think of it, maybe we should resurrect wrangler build for wrangler deploy --dry-run 🤔)
(these are only semi-serious suggestions)

[penalosa]

I agree–we should definitely resurrect wrangler build!

In terms of the command structure here, I went with check startup since it seemed feasible that we might want to have other check * commands in future (check types? check config?), but since this is an alpha command we can always change that later.

[penalosa]

Pages build already has an outfile, is this supposed to reuse that...?

It's meant to be doing that, yeah—does that seem buggy to you?

[emily-shen]

Pages build already has an outfile, is this supposed to reuse that...?

It's meant to be doing that, yeah—does that seem buggy to you?

Ah no that’s fine, the lack of changes in the pages deploy path just threw me for a moment but it makes sense now.

Will the cpuprofile be generated automatically if a pages deploy fails?