[services] fix dev server hang when FastAPI CLI is used by nsidnev · Pull Request #15274 · vercel/vercel

nsidnev · 2026-02-26T03:18:36Z

When FastAPI CLI is used in multi-service mode, it asks rich to query the terminal color. If another service reads the request at the same time, then rich will never receive a response, which will cause it to hang. This can happen either before the first lines from FastAPI CLI appear or when uvicorn starts. To fix this, the dev server will start with detached process so rich will use the default colors

Note

Low Risk Change

This PR changes child process spawning to use detached mode with stdin ignored instead of inherited, fixing a terminal color query hang issue in dev server - a targeted infrastructure fix with limited scope.

Changes child process stdio from 'inherit' to 'ignore' for stdin in two files
Adds detached: true option to spawn calls for service processes
Adds COLUMNS env var passthrough for terminal width formatting

^{Risk assessment for commit c35104f.}

changeset-bot · 2026-02-26T03:18:42Z

🦋 Changeset detected

Latest commit: c35104f

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

This PR includes changesets to release 2 packages

Name	Type
@vercel/python	Patch
vercel	Patch

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github-actions · 2026-02-26T03:18:54Z

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github-actions · 2026-02-26T03:20:13Z

🧪 Unit Test Strategy

Comparing: 11af8c7 → c35104f (view diff)

Strategy: Affected packages only

✅ Only testing packages that have been modified or depend on modified packages.

Affected packages - 2 (5%)

@vercel/python
vercel

Unaffected packages - 38 (95%)

@vercel-internals/get-package-json
@vercel/backends
@vercel/build-utils
@vercel/cervel
@vercel/cli-auth
@vercel/client
@vercel/config
@vercel/detect-agent
@vercel/edge
@vercel/elysia
@vercel/error-utils
@vercel/express
@vercel/fastify
@vercel/firewall
@vercel/frameworks
@vercel/fs-detectors
@vercel/functions
@vercel/gatsby-plugin-vercel-builder
@vercel/go
@vercel/h3
@vercel/hono
@vercel/hydrogen
@vercel/koa
@vercel/nestjs
@vercel/next
@vercel/node
@vercel/oidc
@vercel/oidc-aws-credentials-provider
@vercel/python-analysis
@vercel/redwood
@vercel/related-projects
@vercel/remix-builder
@vercel/routing-utils
@vercel/ruby
@vercel/rust
@vercel/static-build
@vercel/static-config
examples

Results

Unit tests: Only affected packages will run unit tests
E2E tests: Running in parallel via E2E Tests workflow
Type checks: Only affected packages will run type checks

This comment is automatically generated based on the affected testing strategy

This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## @vercel/routing-utils@6.0.0 ### Major Changes - Allow `routes` to coexist with `rewrites`, `headers`, `redirects`, `cleanUrls`, and `trailingSlash`. ([#15020](#15020)) This is part of our efforts to undeprecate `routes`, which had previously been deprecated for a few years and replaced by the properties above. Now that we are undeprecating `routes` in favor of a more focused deprecation of properties within it, it is now allowed to coexist with the new properties. When used together, `routes` are inserted after `cleanUrls` and `trailingSlash` but before `redirects`, `headers`, and `rewrites` in the routing order. - Deprecate `handle`, `important`, and `override` properties in `routes` schema ([#15015](#15015)) ## @vercel/build-utils@13.6.0 ### Minor Changes - Find entrypoints for django projects. ([#15167](#15167)) ### Patch Changes - Rename fetch to nodeFetch in cases where it is an import from node-fetch ([#15234](#15234)) - [@vercel/build-utils] fix uncaught exception in streamToBuffer when stream exceeds max Buffer size ([#15276](#15276)) - Remove source and destination typo suggestions for routes schema ([#15014](#15014)) - Support function overrides in backends builder ([#15214](#15214)) - Updated dependencies \[[`b3a96cc4f276ce8d16c695eabd499d3a17e73aa8`](b3a96cc)]: - @vercel/python-analysis@0.8.0 ## vercel@50.25.0 ### Minor Changes - Launch auto-provision flow as default for `vercel integration add` and `vercel install`. The `FF_AUTO_PROVISION_INSTALL` flag is now a kill-switch (`=0` to revert) instead of opt-in. ([#15265](#15265)) - [services] make the `experimentalServices` config the primary marker for the services flow ([#15246](#15246)) - Added command to fetch a development OIDC token ([#14785](#14785)) ### Patch Changes - Rename fetch to nodeFetch when importing from node-fetch ([#15232](#15232)) - Add setup/destroy hooks and context handling to the CLI eval runner. ([#15247](#15247)) - [services] fix dev server hang when FastAPI CLI is used ([#15274](#15274)) - Fix `--help` flag to return exit code 0 instead of 2 for the `metrics` command, aligning with standard CLI conventions. ([#15259](#15259)) - Rename fetch to nodeFetch in cases where it is an import from node-fetch ([#15234](#15234)) - Change `vercel metrics` default query output from CSV to rich text with metadata, summary tables, sparklines, and optional raw values via `--raw-values`. ([#15178](#15178)) - Removes the legacy SSO redirect flow code. ([#15228](#15228)) - Updated dependencies \[[`ad86425c3e0a1d1738cef8464dd767dd1d9a0e9a`](ad86425), [`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269), [`d9e3a570a9c6ee47afa3446ec611b6a9e4b4feec`](d9e3a57), [`2db57840669ca2fa8dadf492bd38c21bf9e3cfeb`](2db5784), [`0d42acfd22e51e51cb0e4a5aea7c19f3886ed496`](0d42acf), [`8404a7315260851495d708f1c7c6e870d7ffa007`](8404a73), [`fbf649223e6fa8b509295a85784347dcebd4a0b0`](fbf6492), [`b3a96cc4f276ce8d16c695eabd499d3a17e73aa8`](b3a96cc), [`9a6358529f0737415110cf03d626dc9ee8e99126`](9a63585)]: - @vercel/remix-builder@5.6.0 - @vercel/python@6.17.0 - @vercel/next@4.15.35 - @vercel/node@5.6.8 - @vercel/static-build@2.8.42 - @vercel/build-utils@13.6.0 - @vercel/go@3.4.3 - @vercel/backends@0.0.38 - @vercel/elysia@0.1.41 - @vercel/express@0.1.50 - @vercel/fastify@0.1.44 - @vercel/h3@0.1.50 - @vercel/hono@0.2.44 - @vercel/koa@0.1.24 - @vercel/nestjs@0.2.45 - @vercel/redwood@2.4.9 - @vercel/rust@1.0.5 - @vercel/hydrogen@1.3.5 - @vercel/ruby@2.3.2 ## @vercel/python@6.17.0 ### Minor Changes - Find entrypoints for django projects. ([#15167](#15167)) ### Patch Changes - Rename fetch to nodeFetch when importing from node-fetch ([#15232](#15232)) - [services] fix dev server hang when FastAPI CLI is used ([#15274](#15274)) - [python] fix dev server crash on relative imports ([#15269](#15269)) - Updated dependencies \[[`b3a96cc4f276ce8d16c695eabd499d3a17e73aa8`](b3a96cc)]: - @vercel/python-analysis@0.8.0 ## @vercel/python-analysis@0.8.0 ### Minor Changes - Find entrypoints for django projects. ([#15167](#15167)) ## @vercel/remix-builder@5.6.0 ### Minor Changes - [remix] Support future.v8_middleware option ([#15189](#15189)) ## @vercel/backends@0.0.38 ### Patch Changes - Support function overrides in backends builder ([#15214](#15214)) - Updated dependencies \[[`2db57840669ca2fa8dadf492bd38c21bf9e3cfeb`](2db5784), [`0d42acfd22e51e51cb0e4a5aea7c19f3886ed496`](0d42acf), [`8404a7315260851495d708f1c7c6e870d7ffa007`](8404a73), [`b3a96cc4f276ce8d16c695eabd499d3a17e73aa8`](b3a96cc), [`9a6358529f0737415110cf03d626dc9ee8e99126`](9a63585)]: - @vercel/build-utils@13.6.0 ## @vercel/cervel@0.0.25 ### Patch Changes - Updated dependencies \[[`9a6358529f0737415110cf03d626dc9ee8e99126`](9a63585)]: - @vercel/backends@0.0.38 ## @vercel/client@17.2.48 ### Patch Changes - rename fetch to fetchApi ([#15231](#15231)) - Updated dependencies \[[`e64a85daec784b4fe571abe7405a80aca150007a`](e64a85d), [`2db57840669ca2fa8dadf492bd38c21bf9e3cfeb`](2db5784), [`0d42acfd22e51e51cb0e4a5aea7c19f3886ed496`](0d42acf), [`8404a7315260851495d708f1c7c6e870d7ffa007`](8404a73), [`b3a96cc4f276ce8d16c695eabd499d3a17e73aa8`](b3a96cc), [`9a6358529f0737415110cf03d626dc9ee8e99126`](9a63585), [`af6a651229cad4ddb7fcc15bd14d06355c2b77ee`](af6a651)]: - @vercel/routing-utils@6.0.0 - @vercel/build-utils@13.6.0 ## @vercel/config@0.0.35 ### Patch Changes - Updated dependencies \[[`e64a85daec784b4fe571abe7405a80aca150007a`](e64a85d), [`af6a651229cad4ddb7fcc15bd14d06355c2b77ee`](af6a651)]: - @vercel/routing-utils@6.0.0 ## @vercel/elysia@0.1.41 ### Patch Changes - Updated dependencies \[[`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269)]: - @vercel/node@5.6.8 ## @vercel/express@0.1.50 ### Patch Changes - Updated dependencies \[[`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269)]: - @vercel/node@5.6.8 - @vercel/cervel@0.0.25 ## @vercel/fastify@0.1.44 ### Patch Changes - Updated dependencies \[[`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269)]: - @vercel/node@5.6.8 ## @vercel/frameworks@3.19.1 ### Patch Changes - Rename fetch to nodeFetch when importing from node-fetch ([#15232](#15232)) ## @vercel/fs-detectors@5.8.12 ### Patch Changes - Support function overrides in backends builder ([#15214](#15214)) - Updated dependencies \[[`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269), [`e64a85daec784b4fe571abe7405a80aca150007a`](e64a85d), [`af6a651229cad4ddb7fcc15bd14d06355c2b77ee`](af6a651)]: - @vercel/frameworks@3.19.1 - @vercel/routing-utils@6.0.0 ## @vercel/gatsby-plugin-vercel-builder@2.0.140 ### Patch Changes - Updated dependencies \[[`2db57840669ca2fa8dadf492bd38c21bf9e3cfeb`](2db5784), [`0d42acfd22e51e51cb0e4a5aea7c19f3886ed496`](0d42acf), [`8404a7315260851495d708f1c7c6e870d7ffa007`](8404a73), [`b3a96cc4f276ce8d16c695eabd499d3a17e73aa8`](b3a96cc), [`9a6358529f0737415110cf03d626dc9ee8e99126`](9a63585)]: - @vercel/build-utils@13.6.0 ## @vercel/go@3.4.3 ### Patch Changes - Rename fetch to nodeFetch in cases where it is an import from node-fetch ([#15234](#15234)) ## @vercel/h3@0.1.50 ### Patch Changes - Updated dependencies \[[`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269)]: - @vercel/node@5.6.8 ## @vercel/hono@0.2.44 ### Patch Changes - Updated dependencies \[[`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269)]: - @vercel/node@5.6.8 ## @vercel/koa@0.1.24 ### Patch Changes - Updated dependencies \[[`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269)]: - @vercel/node@5.6.8 ## @vercel/nestjs@0.2.45 ### Patch Changes - Updated dependencies \[[`3d872692c601abeec98743d2af3a3ea19587e799`](3d87269)]: - @vercel/node@5.6.8 ## @vercel/next@4.15.35 ### Patch Changes - Rename fetch to nodeFetch when importing from node-fetch ([#15232](#15232)) ## @vercel/node@5.6.8 ### Patch Changes - Rename fetch to nodeFetch when importing from node-fetch ([#15232](#15232)) - Updated dependencies \[[`2db57840669ca2fa8dadf492bd38c21bf9e3cfeb`](2db5784), [`0d42acfd22e51e51cb0e4a5aea7c19f3886ed496`](0d42acf), [`8404a7315260851495d708f1c7c6e870d7ffa007`](8404a73), [`b3a96cc4f276ce8d16c695eabd499d3a17e73aa8`](b3a96cc), [`9a6358529f0737415110cf03d626dc9ee8e99126`](9a63585)]: - @vercel/build-utils@13.6.0 ## @vercel/static-build@2.8.42 ### Patch Changes - Rename fetch to nodeFetch in cases where it is an import from node-fetch ([#15234](#15234)) - Updated dependencies \[]: - @vercel/gatsby-plugin-vercel-builder@2.0.140 ## @vercel/python-runtime@0.5.2 ### Patch Changes - fix ASGI lifecycle events in non-IPC codepath ([#15268](#15268)) ## @vercel/python-workers@0.0.11 ### Patch Changes - Add a version bump for `@vercel/python-workers` so previously merged changes are included in the next release. ([#15254](#15254))  > [!NOTE] > Low Risk Change > > This PR is an automated Changesets release that only updates version numbers in package.json files and CHANGELOG.md files across multiple packages, with no logic or schema changes. > > - Version bumps across ~30 packages (package.json version fields) > - CHANGELOG.md updates documenting previously merged changes > - Deletion of .changeset/*.md files consumed by release automation > > <sup>Risk assessment for [commit 9b78e59](https://github.com/vercel/vercel/commit/9b78e59c7c4716d10beac3a0228e767c8565f65a).</sup>  Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

[services] fix dev server hang when FastAPI CLI is used

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nsidnev requested review from a team as code owners February 26, 2026 03:18

Merge branch 'main' into nsidnev/fix-fastapi-dev-hang

c35104f

vercel bot deployed to Preview February 26, 2026 03:25 View deployment

ricardo-agz approved these changes Feb 26, 2026

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nsidnev merged commit d9e3a57 into main Feb 26, 2026
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nsidnev deleted the nsidnev/fix-fastapi-dev-hang branch February 26, 2026 03:55

vercel-release-bot mentioned this pull request Feb 26, 2026

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[services] fix dev server hang when FastAPI CLI is used#15274

[services] fix dev server hang when FastAPI CLI is used#15274
nsidnev merged 2 commits intomainfrom
nsidnev/fix-fastapi-dev-hang

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