trailofbits-dropkit/CLAUDE.md

dropkit

CLI tool for managing DigitalOcean droplets for Trail of Bits engineers. Pre-configured cloud-init, Tailscale VPN (enabled by default), and SSH config management.

Critical Rules ⚠️

• Never use pip — always use uv for all Python operations
• Always run prek run before committing (or prek install to auto-run on commit)
• Keep README.md in sync when adding commands or features

Quick Commands

uv sync                      # Install dependencies
prek install                 # Set up pre-commit hooks (one-time)
prek run                     # Run all checks (ruff, ty, shellcheck, etc.)
uv run pytest                # Run tests
uv run dropkit --help        # CLI help

Project Structure

dropkit/
├── pyproject.toml              # Dependencies and metadata
├── CLAUDE.md                   # This file
├── README.md                   # User documentation
├── dropkit/
│   ├── main.py                 # Typer CLI entry point
│   ├── config.py               # Config with SSH key validation
│   ├── api.py                  # DigitalOcean REST API (see docstring for endpoints)
│   ├── cloudinit.py            # Cloud-init template rendering
│   ├── ssh_config.py           # SSH config manipulation
│   └── templates/
│       └── default-cloud-init.yaml
└── tests/
    ├── test_api.py
    ├── test_config.py
    ├── test_main_helpers.py
    └── test_ssh_config.py

Technology Stack

• Python 3.11+ with uv (NOT pip)
• CLI: Typer + Rich
• API: Direct REST calls (requests library, no SDK)
• Config: YAML + Pydantic 2.x validation
• Templating: Jinja2 for cloud-init
• Code Quality: Ruff (linter + formatter), ty (types)

Key Conventions

Username

• Derived from DigitalOcean account email, not configured
• Fetched via /v2/account, sanitized for Linux compatibility
• john.doe@example.com → john_doe

SSH Hostname

• All SSH entries use dropkit.<droplet-name> format
• Centralized in get_ssh_hostname() helper

Tags

• Default tags: owner:<username> and firewall
• Additional tags extend defaults (never replace)
• Used for filtering, billing, and security

SSH Keys

• Only public keys (*.pub) accepted
• Strict validation rejects private keys
• Auto-detects id_ed25519.pub, id_rsa.pub, id_ecdsa.pub

Tailscale VPN

• Enabled by default for new droplets
• Locks down UFW to only allow tailscale0 interface
• Disable with --no-tailscale flag

Architecture Decisions

1. Username from email — Not stored in config; fetched from DO API on demand. Ensures consistency across machines.

2. SSH key validation — Prevents accidental private key upload. Validates format (ssh-rsa, ssh-ed25519, ecdsa-sha2-*, etc.).

3. Tags extend defaults — --tags adds to defaults, never replaces. Ensures owner tag always present.

4. Direct REST API — No python-digitalocean library. Simpler, fewer dependencies, full control.

5. Tailscale by default — Secure VPN access without public SSH. Local Tailscale required; keeps public IP if local Tailscale not running.

6. Pydantic validation — Runtime type safety for config files. Clear errors for invalid configurations.

7. SSH config backups — Created at ~/.ssh/config.bak before modifications. Each backup overwrites previous.

Gotchas & Troubleshooting

Cloud-init JSON parsing (CRITICAL)

cloud-init status --format=json may return non-zero exit code but valid JSON. Always parse JSON regardless of subprocess return code.

# CORRECT: Parse JSON even on error
result = subprocess.run([...], capture_output=True)
data = json.loads(result.stdout)  # Don't check returncode first

# WRONG: Checking returncode before parsing
if result.returncode == 0:  # May skip valid JSON with error status
    data = json.loads(result.stdout)

Status values: "done" (success), "error" (failed), "running" (in progress).

Disk resize is permanent

Cannot be undone. Use --no-disk to resize only CPU/memory.

SSH config backups overwrite

Only keeps one backup at ~/.ssh/config.bak.

Development

Package Management

uv add <package>             # Add dependency
uv add --dev <package>       # Add dev dependency
uv sync                      # Install all
uv run <command>             # Run in venv

Linting

prek run                     # Run all checks (required before commit)
prek run --all-files         # Check all files, not just staged
uv run ruff check --fix .    # Lint + autofix only
uv run ty check dropkit/     # Type check only

Ruff config: Python 3.11+, 100-char lines, modern syntax (str | None, list[str]).

Testing

uv run pytest                              # All tests
uv run pytest tests/test_api.py            # Specific file
uv run pytest -k "validate_ssh"            # Pattern match
uv run pytest -v                           # Verbose

Pydantic Models

• DropkitConfig — Root config with extra='forbid'
• DigitalOceanConfig — API token validation
• DefaultsConfig — Region, size, image slugs
• CloudInitConfig — Template path, SSH keys (min 1)
• SSHConfig — SSH config path, identity file
• TailscaleConfig — VPN settings (enabled, lock_down_firewall, auth_timeout)

Config files: ~/.config/dropkit/config.yaml, ~/.config/dropkit/cloud-init.yaml

Shell Completion

dropkit --install-completion zsh  # Enable tab completion

Provides dynamic completion for droplet names (filtered by owner tag).