[python] Lambda runtime install cold-start performance improvements by gscho · Pull Request #15080 · vercel/vercel

gscho · 2026-02-17T18:28:54Z

Warning

High Risk Change

Large refactor of Python Lambda dependency bundling logic introduces new knapsack packing algorithm and changes runtime installation from uv pip install to uv sync --inexact --frozen, affecting cold-start behavior for oversized bundles.

New PythonDependencyExternalizer class with knapsack algorithm for optimal Lambda packing
Runtime install switches from uv pip install -r requirements.txt to uv sync --inexact --frozen
Removes generateRuntimeRequirements function, replaces with JSON config-based approach

^{Risk assessment for commit 870da37.}

Signed-off-by: gscho <greg.c.schofield@gmail.com>

changeset-bot · 2026-02-17T18:29:04Z

🦋 Changeset detected

Latest commit: 870da37

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

This PR includes changesets to release 18 packages

Name	Type
@vercel/python-analysis	Minor
@vercel/python-runtime	Minor
@vercel/python	Minor
@vercel/build-utils	Patch
vercel	Patch
@vercel/backends	Patch
@vercel/client	Patch
@vercel/elysia	Patch
@vercel/express	Patch
@vercel/fastify	Patch
@vercel/gatsby-plugin-vercel-builder	Patch
@vercel/h3	Patch
@vercel/hono	Patch
@vercel/koa	Patch
@vercel/nestjs	Patch
@vercel/node	Patch
@vercel/static-build	Patch
@vercel/cervel	Patch

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github-actions · 2026-02-17T18:29:57Z

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github-actions · 2026-02-17T18:32:50Z

🧪 Unit Test Strategy

Comparing: 847ea59 → 870da37 (view diff)

Strategy: Code changed outside of a package - running all unit tests

⚠️ All unit tests will run because global code changes could impact all packages.

Affected packages - 40 (100%)

@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
@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
vercel

Results

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

This comment is automatically generated based on the affected testing strategy

Signed-off-by: gscho <greg.c.schofield@gmail.com>

packages/python/src/runtime-dep-install.ts

Signed-off-by: gscho <greg.c.schofield@gmail.com>

python/vercel-runtime/src/vercel_runtime/vc_init.py

Signed-off-by: gscho <greg.c.schofield@gmail.com>

python/vercel-runtime/src/vercel_runtime/vc_init.py

packages/python/package-python-devel/.gitignore

packages/python/src/dependency-externalizer.ts

Signed-off-by: gscho <greg.c.schofield@gmail.com>

Co-authored-by: Elvis Pranskevichus <elvis@vercel.com>

…el/vercel into gscho/PY-99-pack-the-lambda

Signed-off-by: gscho <greg.c.schofield@gmail.com>

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@50.22.0 ### Minor Changes - feat(cli): add `vercel integration guide` command ([#15108](#15108)) Adds a new `vercel integration guide` subcommand that displays getting started guides, code snippets, and resource links for marketplace integrations directly in the terminal. Supports single-product and multi-product integrations with interactive product and framework selection. Includes `--framework` flag for non-interactive framework selection (useful for CI/agents). Output is raw markdown written to stdout for easy piping to files or other tools. ### Patch Changes - fix(cli): fix missing planId in non-subscription plan web fallback ([#15152](#15152)) - [services]([#15093](#15093)) - consolidate `workspace` and `entrypoint` from `experimentalServices` `vercel.json` schema - make `framework` config in service optional -- infer framework from service workspace when not explicitly provided - Updated dependencies \[[`09b3540742ac86b768de9775929fef1ef36db412`](09b3540), [`fc56fb91b4dafabe0f68f86efeabbaf98b2642bc`](fc56fb9)]: - @vercel/build-utils@13.4.3 - @vercel/python@6.15.0 - @vercel/backends@0.0.36 - @vercel/elysia@0.1.39 - @vercel/express@0.1.48 - @vercel/fastify@0.1.42 - @vercel/go@3.4.1 - @vercel/h3@0.1.48 - @vercel/hono@0.2.42 - @vercel/hydrogen@1.3.5 - @vercel/koa@0.1.22 - @vercel/nestjs@0.2.43 - @vercel/next@4.15.31 - @vercel/node@5.6.6 - @vercel/redwood@2.4.9 - @vercel/remix-builder@5.5.10 - @vercel/ruby@2.3.1 - @vercel/rust@1.0.5 - @vercel/static-build@2.8.40 ## @vercel/python@6.15.0 ### Minor Changes - Optimize cold starts for lambdas >250MB ([#15080](#15080)) 1. Remove `uv pip install` and replace it with `uv sync --inexact --frozen` 2. Pack the lambda zip with dependencies up to 245MB then only install the remaining ones at runtime ### Patch Changes - Updated dependencies \[[`fc56fb91b4dafabe0f68f86efeabbaf98b2642bc`](fc56fb9)]: - @vercel/python-analysis@0.6.0 ## @vercel/python-analysis@0.6.0 ### Minor Changes - Optimize cold starts for lambdas >250MB ([#15080](#15080)) 1. Remove `uv pip install` and replace it with `uv sync --inexact --frozen` 2. Pack the lambda zip with dependencies up to 245MB then only install the remaining ones at runtime ## @vercel/backends@0.0.36 ### Patch Changes - Updated dependencies \[[`09b3540742ac86b768de9775929fef1ef36db412`](09b3540)]: - @vercel/build-utils@13.4.3 ## @vercel/build-utils@13.4.3 ### Patch Changes - [services]([#15093](#15093)) - consolidate `workspace` and `entrypoint` from `experimentalServices` `vercel.json` schema - make `framework` config in service optional -- infer framework from service workspace when not explicitly provided - Updated dependencies \[[`fc56fb91b4dafabe0f68f86efeabbaf98b2642bc`](fc56fb9)]: - @vercel/python-analysis@0.6.0 ## @vercel/cervel@0.0.23 ### Patch Changes - Updated dependencies \[]: - @vercel/backends@0.0.36 ## @vercel/client@17.2.45 ### Patch Changes - Updated dependencies \[[`09b3540742ac86b768de9775929fef1ef36db412`](09b3540)]: - @vercel/build-utils@13.4.3 ## @vercel/elysia@0.1.39 ### Patch Changes - Updated dependencies \[]: - @vercel/node@5.6.6 ## @vercel/express@0.1.48 ### Patch Changes - Updated dependencies \[]: - @vercel/node@5.6.6 - @vercel/cervel@0.0.23 ## @vercel/fastify@0.1.42 ### Patch Changes - Updated dependencies \[]: - @vercel/node@5.6.6 ## @vercel/fs-detectors@5.8.9 ### Patch Changes - [services]([#15093](#15093)) - consolidate `workspace` and `entrypoint` from `experimentalServices` `vercel.json` schema - make `framework` config in service optional -- infer framework from service workspace when not explicitly provided ## @vercel/gatsby-plugin-vercel-builder@2.0.138 ### Patch Changes - Updated dependencies \[[`09b3540742ac86b768de9775929fef1ef36db412`](09b3540)]: - @vercel/build-utils@13.4.3 ## @vercel/h3@0.1.48 ### Patch Changes - Updated dependencies \[]: - @vercel/node@5.6.6 ## @vercel/hono@0.2.42 ### Patch Changes - Updated dependencies \[]: - @vercel/node@5.6.6 ## @vercel/koa@0.1.22 ### Patch Changes - Updated dependencies \[]: - @vercel/node@5.6.6 ## @vercel/nestjs@0.2.43 ### Patch Changes - Updated dependencies \[]: - @vercel/node@5.6.6 ## @vercel/node@5.6.6 ### Patch Changes - Updated dependencies \[[`09b3540742ac86b768de9775929fef1ef36db412`](09b3540)]: - @vercel/build-utils@13.4.3 ## @vercel/static-build@2.8.40 ### Patch Changes - Updated dependencies \[]: - @vercel/gatsby-plugin-vercel-builder@2.0.138 ## @vercel/python-runtime@0.5.0 ### Minor Changes - Optimize cold starts for lambdas >250MB ([#15080](#15080)) 1. Remove `uv pip install` and replace it with `uv sync --inexact --frozen` 2. Pack the lambda zip with dependencies up to 245MB then only install the remaining ones at runtime  > [!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 changes. > > - Version bumps across ~25 packages (patch and minor versions) > - CHANGELOG.md updates documenting previous changes > - Deleted changeset markdown files consumed by release process > > <sup>Risk assessment for [commit f054c83](https://github.com/vercel/vercel/commit/f054c83041bfd8d833afeb59bac76918875f980e).</sup>  Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

gscho added 3 commits February 17, 2026 13:26

Remove generateRuntimeRequirements

fb7ea0e

Signed-off-by: gscho <greg.c.schofield@gmail.com>

Ensure pyproject.toml and uv.lock files are bundled in the lambda zip.

774a826

Signed-off-by: gscho <greg.c.schofield@gmail.com>

Switch from uv pip install to uv sync --inexact.

2ca1441

Signed-off-by: gscho <greg.c.schofield@gmail.com>

gscho added the run-e2e-tests label Feb 17, 2026

vercel bot deployed to Preview February 17, 2026 18:29 View deployment

Merged main.

938c5a2

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 18, 2026 15:08 View deployment

Add UV_NO_CACHE to prevent uv from writing outside of /tmp.

bbf6e40

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 18, 2026 16:00 View deployment

Force uv to use existing venv.

1453c0e

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 18, 2026 16:26 View deployment

Explicitly skip installing bundled packages with uv sync.

9e77c23

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 18, 2026 17:01 View deployment

Prevent uv sync output from writing to STDERR on successful installs.

b3aa314

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 18, 2026 18:34 View deployment

gscho added 4 commits February 18, 2026 14:34

Write messages as [info] intstead of [error].

c20ee6d

Signed-off-by: gscho <greg.c.schofield@gmail.com>

Pack the lambda as full as possible up to the configured limit.

18ad0b4

Signed-off-by: gscho <greg.c.schofield@gmail.com>

Refactor the runtime dep install logic into its own files.

3dba383

Signed-off-by: gscho <greg.c.schofield@gmail.com>

Clean up the slop.

e2757ce

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 18, 2026 20:34 View deployment

vercel bot reviewed Feb 18, 2026

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packages/python/src/runtime-dep-install.ts Outdated Show resolved Hide resolved

Remove env var for lambda pack size.

b0c36a2

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 18, 2026 20:42 View deployment

Merged main.

d0053f5

Signed-off-by: gscho <greg.c.schofield@gmail.com>

gscho force-pushed the gscho/PY-99-pack-the-lambda branch from 4f7edb8 to d0053f5 Compare February 18, 2026 20:47

vercel bot deployed to Preview February 18, 2026 20:47 View deployment

Refactor into its own RuntimeDependencyInstall class.

bb16b22

Signed-off-by: gscho <greg.c.schofield@gmail.com>

gscho marked this pull request as ready for review February 19, 2026 17:08

gscho requested review from a team as code owners February 19, 2026 17:08

Undo formatting changes.

2dc8cca

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 19, 2026 17:19 View deployment

gscho commented Feb 19, 2026

View reviewed changes

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Merge branch 'main' into gscho/PY-99-pack-the-lambda

42b1417

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Merge branch 'main' into gscho/PY-99-pack-the-lambda

c3993be

vercel bot deployed to Preview February 19, 2026 18:10 View deployment

Fix lint error.

2bda351

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 19, 2026 18:21 View deployment

elprans reviewed Feb 19, 2026

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gscho and others added 3 commits February 19, 2026 14:33

Remove dir committed by mistake.

bba39f4

Signed-off-by: gscho <greg.c.schofield@gmail.com>

Apply suggestions from code review

6d49ac2

Co-authored-by: Elvis Pranskevichus <elvis@vercel.com>

Merge branch 'gscho/PY-99-pack-the-lambda' of https://github.com/verc…

88db5e3

…el/vercel into gscho/PY-99-pack-the-lambda

vercel bot deployed to Preview February 19, 2026 19:35 View deployment

gscho added 2 commits February 19, 2026 14:39

Merged main.

337f402

Signed-off-by: gscho <greg.c.schofield@gmail.com>

Add back --no-cache and set link mode back to copy.

34391b5

Signed-off-by: gscho <greg.c.schofield@gmail.com>

vercel bot deployed to Preview February 19, 2026 19:43 View deployment

Add changeset.

870da37

Signed-off-by: gscho <greg.c.schofield@gmail.com>

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gscho requested a review from elprans February 19, 2026 20:18

elprans approved these changes Feb 19, 2026

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gscho merged commit fc56fb9 into main Feb 19, 2026
395 of 400 checks passed

gscho deleted the gscho/PY-99-pack-the-lambda branch February 19, 2026 21:49

vercel-release-bot mentioned this pull request Feb 19, 2026

Version Packages #15153

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[python] Lambda runtime install cold-start performance improvements#15080

[python] Lambda runtime install cold-start performance improvements#15080
gscho merged 38 commits intomainfrom
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