Development Guide

This document contains information for developers working on the Reaper project.

Development Setup
Building
Testing
Code Quality
Git Hooks
Docker (Optional)
VS Code Setup
CI/CD
Coverage
Contributing

Development Setup

Prerequisites

Rust toolchain (we pin stable via rust-toolchain.toml)
Docker (optional, for Linux-specific testing on macOS)
Ansible (for deploying to clusters)

Clone and Build

git clone https://github.com/miguelgila/reaper
cd reaper
cargo build

The repository includes rust-toolchain.toml which automatically pins the Rust toolchain version and enables rustfmt and clippy components.

Building

Local Build (Debug)

cargo build

Binaries are output to target/debug/.

Release Build

cargo build --release

Binaries are output to target/release/.

Static Musl Build (for Kubernetes deployment)

For deployment to Kubernetes clusters, we build static musl binaries:

# Install musl target (one-time setup)
rustup target add x86_64-unknown-linux-musl

# Build static binary
docker run --rm \
  -v "$(pwd)":/work \
  -w /work \
  messense/rust-musl-cross:x86_64-musl \
  cargo build --release --target x86_64-unknown-linux-musl

This produces binaries at target/x86_64-unknown-linux-musl/release/ that work in containerized environments (like Kind nodes).

For aarch64:

rustup target add aarch64-unknown-linux-musl

docker run --rm \
  -v "$(pwd)":/work \
  -w /work \
  messense/rust-musl-cross:aarch64-musl \
  cargo build --release --target aarch64-unknown-linux-musl

Testing

See TESTING.md for comprehensive testing documentation.

Quick Reference

# Unit tests (fast, recommended for local development)
cargo test

# Full integration tests (Kubernetes + unit tests)
./scripts/run-integration-tests.sh

# Integration tests (K8s only, skip cargo tests)
./scripts/run-integration-tests.sh --skip-cargo

# Coverage report (requires Docker)
./scripts/docker-coverage.sh

Test Modules

tests/integration_basic_binary.rs - Basic runtime functionality (create/start/state/delete)
tests/integration_user_management.rs - User/group ID handling, umask
tests/integration_shim.rs - Shim-specific tests
tests/integration_io.rs - FIFO stdout/stderr redirection
tests/integration_exec.rs - Exec into running containers
tests/integration_overlay.rs - Overlay filesystem tests

Run a specific test suite:

cargo test --test integration_basic_binary

Code Quality

Formatting

Format all code before committing:

cargo fmt --all

Check formatting without making changes:

cargo fmt --all -- --check

Linting

Run clippy to catch common mistakes and improve code quality:

# Quick check
cargo clippy --all-targets --all-features

# Match CI exactly (treats warnings as errors)
cargo clippy -- -D warnings

CI runs clippy with -D warnings, so any warning is a hard failure. The pre-push hook runs this automatically if you've installed hooks via ./scripts/install-hooks.sh.

Linux Cross-Check (macOS only)

The overlay module (src/bin/reaper-runtime/overlay.rs) is gated by #[cfg(target_os = "linux")] and doesn't compile on macOS. To catch compilation errors in Linux-only code:

# One-time setup
rustup target add x86_64-unknown-linux-gnu

# Check compilation for Linux target
cargo clippy --target x86_64-unknown-linux-gnu --all-targets --all-features

Git Hooks

We provide git hooks in .githooks/ to catch issues before they reach CI.

Enable Hooks

./scripts/install-hooks.sh

This sets core.hooksPath to .githooks/ and marks the hooks executable. Since the hooks are checked into the repo, every contributor gets the same setup.

Available Hooks

Hook	Runs	Purpose
`pre-commit`	`cargo fmt --all`	Auto-formats code and stages changes before each commit
`pre-push`	`cargo clippy -- -D warnings`	Catches lint issues before pushing (matches CI)

The pre-push hook mirrors the exact clippy invocation used in CI, so pushes that pass locally will pass the CI clippy check too.

Customization

pre-commit: To fail on unformatted code instead of auto-fixing, change cargo fmt --all to cargo fmt --all -- --check and remove the re-staging logic.
pre-push: To skip clippy for a one-off push, use git push --no-verify.

Docker (Optional)

Docker is not required for local development on macOS. Prefer cargo test locally for speed.

Use Docker when you need:

Code coverage via cargo-tarpaulin (Linux-first tool)
CI failure reproduction specific to Linux
Static musl binary builds for Kubernetes

Run Coverage in Docker

./scripts/docker-coverage.sh

This runs cargo-tarpaulin in a Linux container with appropriate capabilities.

VS Code Setup

Recommended Extensions

rust-analyzer — Main Rust language support
CodeLLDB (vadimcn.vscode-lldb) — Debug adapter for Rust
Test Explorer UI — Unified test UI

Configure rust-analyzer to run clippy on save and enable CodeLens for inline run/debug buttons.

CI/CD

GitHub Actions workflows run on pushes and pull requests to main:

CI Workflow (`ci.yml`)

A single unified pipeline that runs:

cargo fmt -- --check (formatting)
cargo clippy --workspace --all-targets -- -D warnings (linting)
cargo audit (dependency vulnerability scan)
cargo test --verbose (unit tests)
cargo tarpaulin → Codecov upload (coverage)
Cross-compile static musl binaries (all binaries)
Kind integration tests (run-integration-tests.sh --skip-cargo)
Example validation (test-examples.sh --skip-cluster)

Coverage

Local Coverage (Linux)

If running on Linux, you can use tarpaulin directly:

cargo install cargo-tarpaulin
cargo tarpaulin --out Xml --timeout 600

Coverage via Docker (macOS/Windows)

Run the included Docker script:

./scripts/docker-coverage.sh

Configuration lives in tarpaulin.toml. Functions requiring root + Linux namespaces (tested by kind-integration) are excluded via #[cfg(not(tarpaulin_include))] so coverage reflects what unit tests can actually reach.

Contributing

Before Opening a PR

Format code:
```
cargo fmt --all
```

Run linting:

cargo clippy --all-targets --all-features

Run tests:
```
cargo test
```
Optional: Run integration tests:
```
./scripts/run-integration-tests.sh
```
Install git hooks (auto-formats on commit, runs clippy before push):
```
./scripts/install-hooks.sh
```

Development Workflow

For fast feedback during development:

# Quick iteration cycle
cargo test              # Unit tests (seconds)
cargo clippy            # Linting

# Before pushing
cargo fmt --all         # Format code
cargo test              # All unit tests
./scripts/run-integration-tests.sh  # Full validation

Integration Test Iteration

If you're iterating on overlay or shim logic:

# First run (build cluster, binaries, tests)
./scripts/run-integration-tests.sh --no-cleanup

# Make code changes...

# Rebuild and test (skip cargo, reuse cluster)
cargo build --release --bin containerd-shim-reaper-v2 --bin reaper-runtime
./scripts/run-integration-tests.sh --skip-cargo --no-cleanup

# Repeat until satisfied...

# Final cleanup run
./scripts/run-integration-tests.sh --skip-cargo

Project Structure

reaper/
├── src/
│   ├── bin/
│   │   ├── containerd-shim-reaper-v2/  # Shim binary
│   │   │   └── main.rs                 # Shim implementation
│   │   └── reaper-runtime/             # Runtime binary
│   │       ├── main.rs                 # OCI runtime CLI
│   │       ├── state.rs                # State persistence
│   │       └── overlay.rs              # Overlay filesystem (Linux)
├── tests/                              # Integration tests
├── scripts/                            # Installation and testing scripts
├── deploy/
│   ├── ansible/                        # Ansible playbooks for deployment
│   └── kubernetes/                     # Kubernetes manifests
├── docs/                               # Documentation
└── .githooks/                          # Git hooks (pre-commit, pre-push)

Common Tasks

Add a New Binary

Create directory under src/bin/<binary-name>/
Add main.rs in that directory

Add entry to Cargo.toml:

[[bin]]
name = "binary-name"
path = "src/bin/binary-name/main.rs"

Add a New Test Suite

Create tests/integration_<name>.rs
Use #[test] or #[tokio::test] for async tests
Run with cargo test --test integration_<name>

Update Dependencies

# Check for outdated dependencies
cargo outdated

# Update to latest compatible versions
cargo update

# Update Cargo.lock and check tests still pass
cargo test

Debug a Test

Use VS Code's debug launch configurations or run with logging:

RUST_LOG=debug cargo test <test-name> -- --nocapture

Troubleshooting

Clippy Errors on macOS for Linux-only Code

Run clippy with Linux target:

cargo clippy --target x86_64-unknown-linux-gnu --all-targets

Tests Fail with "Permission Denied"

Some tests require root for namespace operations. Run:

sudo cargo test

Or use integration tests which run in Kind (isolated environment):

./scripts/run-integration-tests.sh

Docker Build Fails

Ensure Docker is running:

docker ps

If Docker daemon is not accessible, start Docker Desktop or the Docker daemon.

Integration Tests Timeout

Increase timeout or check cluster resources:

kubectl get nodes
kubectl describe pod <pod-name>

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