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Contributing guide#

Development environment#

Development tasks are managed with mise. Run mise tasks to see all available tasks.

Prerequisites#

Setup#

# Trust the mise configuration and install tools
mise trust
mise install

# Create Python virtualenv and install dependencies
uv venv
uv sync --all-groups

Building#

Cog is composed of three components that are built separately:

  • Python SDK (python/cog/) — the Python library that model authors use. Built into a wheel that gets installed inside containers.
  • Coglet (crates/) — a Rust prediction server that runs inside containers. Cross-compiled into a Linux wheel.
  • Cog CLI (cmd/cog/, pkg/) — the Go command-line tool. Embeds the SDK wheel and picks up the coglet wheel from dist/.
# Build everything and install
mise run build:sdk                        # build the Python SDK wheel
mise run build:coglet:wheel:linux-x64     # cross-compile the coglet wheel for Linux containers
mise run build:cog                        # build the Go CLI (embeds SDK, picks up coglet from dist/)
sudo mise run install                     # symlink the binary to /usr/local/bin

After making changes, rebuild only the component you changed and then build:cog:

mise run build:sdk                        # after changing python/cog/
mise run build:coglet:wheel:linux-x64     # after changing crates/
mise run build:cog                        # after changing cmd/cog/ or pkg/, or to pick up new wheels

Common tasks#

# Run all tests
mise run test:go
mise run test:python
mise run test:rust

# Run specific tests
mise run test:go -- ./pkg/config
uv run tox -e py312-tests -- python/tests/server/test_http.py -k test_name

# Format code (all languages)
mise run fmt:fix

# Lint code (all languages)
mise run lint

Run mise tasks for the complete list of available tasks.

If you encounter any errors, see the troubleshooting section below.

Project structure#

As much as possible, this is attempting to follow the Standard Go Project Layout.

  • cmd/ - The root cog command.
  • pkg/cli/ - CLI commands.
  • pkg/config - Everything cog.yaml related.
  • pkg/docker/ - Low-level interface for Docker commands.
  • pkg/dockerfile/ - Creates Dockerfiles.
  • pkg/image/ - Creates and manipulates Cog Docker images.
  • pkg/predict/ - Runs predictions on models.
  • pkg/util/ - Various packages that aren't part of Cog. They could reasonably be separate re-usable projects.
  • python/ - The Cog Python library.
  • integration-tests/ - Go-based integration tests using testscript.
  • tools/compatgen/ - Tool for generating CUDA/PyTorch/TensorFlow compatibility matrices.

For deeper architectural understanding, see the architecture documentation.

Updating compatibility matrices#

The CUDA base images and framework compatibility matrices in pkg/config/ are checked into source control and only need to be regenerated when adding support for new versions of CUDA, PyTorch, or TensorFlow.

To regenerate the compatibility matrices, run:

# Regenerate all matrices
mise run generate:compat

# Or regenerate specific matrices
mise run generate:compat cuda
mise run generate:compat torch
mise run generate:compat tensorflow

The generated files are: - pkg/config/cuda_base_images.json - Available NVIDIA CUDA base images - pkg/config/torch_compatibility_matrix.json - PyTorch/CUDA/Python compatibility - pkg/config/tf_compatibility_matrix.json - TensorFlow/CUDA/Python compatibility

CI tool dependencies#

Development tools are managed in two places that must be kept in sync:

  1. mise.toml — Tool versions for local development (uses aqua backend for prebuilt binaries)
  2. .github/workflows/ci.yaml — Tool installation for CI (uses dedicated GitHub Actions)

CI deliberately avoids aqua downloads from GitHub Releases to prevent transient 502 failures. Instead, it uses dedicated actions (taiki-e/install-action, go install, PyO3/maturin-action, etc.) that are more reliable.

Tools disabled in CI are listed in MISE_DISABLE_TOOLS in ci.yaml.

When updating a tool version, update both: - The version in mise.toml (for local dev) - The corresponding version pin in .github/workflows/ci.yaml (for CI)

See the CI Tool Dependencies section in AGENTS.md for the full mapping of tools to their CI installation methods.

Concepts#

There are a few concepts used throughout Cog that might be helpful to understand.

  • Config: The cog.yaml file.
  • Image: Represents a built Docker image that serves the Cog API, containing a model.
  • Input: Input from a prediction, as key/value JSON object.
  • Model: A user's machine learning model, consisting of code and weights.
  • Output: Output from a prediction, as arbitrarily complex JSON object.
  • Prediction: A single run of the model, that takes input and produces output.
  • Predictor: Defines how Cog runs predictions on a model.

Running tests#

To run the entire test suite:

mise run test:go
mise run test:python
mise run test:rust

To run just the Go unit tests:

mise run test:go

To run just the Python tests:

mise run test:python

[!INFO] This runs the Python test suite across all supported Python versions (3.10-3.13) using tox.

Integration Tests#

Integration tests are in integration-tests/ using testscript. Each test is a self-contained .txtar file in integration-tests/tests/, with some specialized tests as Go test functions in subpackages.

# Run all integration tests
mise run test:integration

# Run a specific test
mise run test:integration string_predictor

# Run fast tests only (skip slow GPU/framework tests)
cd integration-tests && go test -short -v

# Run with a custom cog binary
COG_BINARY=/path/to/cog mise run test:integration

Writing Integration Tests#

When adding new functionality, add integration tests in integration-tests/tests/. They are: - Self-contained (embedded fixtures in .txtar files) - Faster to run (parallel execution with automatic cleanup) - Easier to read and write (simple command script format)

Example test structure:

# Test string predictor
cog build -t $TEST_IMAGE
cog predict $TEST_IMAGE -i s=world
stdout 'hello world'

-- cog.yaml --
build:
  python_version: "3.12"
predict: "predict.py:Predictor"

-- predict.py --
from cog import BasePredictor

class Predictor(BasePredictor):
    def predict(self, s: str) -> str:
        return "hello " + s

For testing cog serve, use cog serve and the curl command:

cog build -t $TEST_IMAGE
cog serve
curl POST /predictions '{"input":{"s":"test"}}'
stdout '"output":"hello test"'

Advanced Test Commands#

For tests that require subprocess initialization or async operations, use retry-curl:

retry-curl - HTTP request with automatic retries:

# Make HTTP request with retry logic (useful for subprocess initialization delays)
# retry-curl [method] [path] [body] [max-attempts] [retry-delay]
retry-curl POST /predictions '{"input":{"s":"test"}}' 30 1s
stdout '"output":"hello test"'

Example: Testing predictor with subprocess in setup

cog build -t $TEST_IMAGE
cog serve

# Use generous retries since setup spawns a background process
retry-curl POST /predictions '{"input":{"s":"test"}}' 30 1s
stdout '"output":"hello test"'

-- predict.py --
class Predictor(BasePredictor):
    def setup(self):
        self.process = subprocess.Popen(["./background.sh"])

    def predict(self, s: str) -> str:
        return "hello " + s

Test Conditions#

Use conditions to control when tests run based on environment:

[short] - Skip slow tests in short mode:

[short] skip 'requires GPU or long build time'

cog build -t $TEST_IMAGE
# ... rest of test

Run with go test -short to skip these tests.

[linux] / [!linux] - Platform-specific tests:

[!linux] skip 'requires Linux'

# Linux-specific test
cog build -t $TEST_IMAGE

[amd64] / [!amd64] - Architecture-specific tests:

[!amd64] skip 'requires amd64 architecture'

# amd64-specific test
cog build -t $TEST_IMAGE

[linux_amd64] - Combined platform and architecture:

[!linux_amd64] skip 'requires Linux on amd64'

# Test that requires both Linux and amd64
cog build -t $TEST_IMAGE

Combining conditions:

Conditions can be negated with !. Examples: - [short] - True when go test -short is used (skip this test in short mode) - [!short] - True when NOT running with -short flag (only run this in full test mode) - [!linux] - True when NOT on Linux - [linux_amd64] - True when on Linux AND amd64

See existing tests in integration-tests/tests/, especially setup_subprocess_*.txtar, for more examples.

Running the docs server#

To run the docs website server locally:

mise run docs:serve

Publishing a release#

This project has a GitHub Actions workflow that uses goreleaser to facilitate the process of publishing new releases. The release process is triggered by manually creating and pushing a new annotated git tag.

Choose a version number#

Deciding what the annotated git tag should be requires some interpretation. Cog generally follows SemVer 2.0.0, and since the major version is 0, the rules get a bit more loose. Broadly speaking, the rules for when to increment the patch version still hold, but backward-incompatible changes will not require incrementing the major version. In this way, the minor version may be incremented whether the changes are additive or subtractive. This all changes once the major version is incremented to 1.

Set up GPG signing (macOS)#

Before creating a signed tag, you'll need to set up GPG signing. On macOS, install GPG using Homebrew:

brew install gnupg

Generate a GPG key for signing:

gpg --quick-generate-key "Your Name <[email protected]>" ed25519 default 0

Configure Git to use your GPG key:

# Get your key ID
gpg --list-secret-keys --keyid-format=long

This will show output like: 

sec   ed25519/ABC123DEF456 2024-01-15 [SC]
      ABC123DEF4567890ABCDEF1234567890ABCDEF12
uid                 [ultimate] Your Name <[email protected]>

The key ID is the part after ed25519/ (in this example, ABC123DEF456).

# Configure Git (replace YOUR_KEY_ID with your actual key ID)
git config --global user.signingkey YOUR_KEY_ID
git config --global commit.gpgsign true

Create a prerelease (optional)#

Prereleases are a useful way to give testers a way to try out new versions of Cog without affecting the documented latest download URL which people normally use to install Cog.

To publish a prerelease version, append a SemVer prerelease identifer like -alpha or -beta to the git tag name. Goreleaser will detect this and mark it as a prerelease in GitHub Releases.

git checkout some-prerelease-branch
git fetch --all --tags
git tag -a v0.1.0-alpha -m "Prerelease v0.1.0"
git push --tags

Create a release#

Run these commands to publish a new release v0.13.12 referencing commit fabdadbead:

git checkout main
git fetch --all --tags
git tag --sign --annotate --message 'Release v0.13.12' v0.13.12 fabdadbead
git push origin v0.13.12

Then visit github.com/replicate/cog/actions to monitor the release process.

Get team approval for the PyPI package#

The release workflow will halt until another member of the team approves the release.

Ping someone on the team to review and approve the release.

Convert your git tag to a GitHub release#

Once the release is published, convert your git tag to a proper GitHub release:

  1. Visit github.com/replicate/cog/tags
  2. Click on your tag
  3. Click "Create release from tag"
  4. Add release notes and publish the release

Troubleshooting#

cog command not found#

The compiled cog binary will be installed in $GOPATH/bin/cog, e.g. ~/go/bin/cog. Make sure that Golang's bin directory is present on your system PATH by adding it to your shell config (.bashrc, .zshrc, etc):

export PATH=~/go/bin:$PATH

Still having trouble? Please open an issue on GitHub.