config-migrator

Config Migrator

A utility for moving configuration files between development, staging, and production environments. It preserves structure, resolves environment-specific placeholders, and validates against optional JSON Schemas.

Features

• Format conversion: Convert between JSON, YAML, and TOML while preserving data types.
• Variable substitution: Replace ${VAR} placeholders with values from a provided mapping or environment.
• Custom transforms: Extend behavior with user-supplied transform functions.
• Validation hook: Run a user-supplied validation callback after migration (e.g., for linting or custom checks).
• Dry-run mode: Preview changes without writing output.

Installation

Place the migrate.py script in your project. It requires Python 3.8+ and PyYAML (pip install PyYAML).

Usage

python migrate.py --input app/config.yaml --output app/config.prod.yaml --format yaml --env prod --transforms ./transforms.py

Options

• --input, --output: Source and destination files.
• --format: Output format (json, yaml, toml).
• --env: Environment name (e.g., dev, prod).
• --transforms: Optional Python file containing apply_transform(data, context) function.
• --validate: Optional Python file containing validate(data, context) function.
• --placeholder-prefix: Prefix for placeholder variables (default ${).

Example

# config.yaml
database:
  host: ${DB_HOST}
  port: 5432

DB_HOST=db.internal python migrate.py --input config.yaml --output out.yaml --env prod

Transform API

If you supply a --transforms file, it must define:

def apply_transform(data, context):
    # data: dict/list of the parsed config
    # context: dict with keys: 'env', 'input_path', 'output_path', 'raw_input'
    # return modified data
    return data

This is evaluated with eval() to allow flexible, user-defined logic. Use only trusted sources.

Validation Hook

Similar to transforms, a validation file should define validate(data, context). It is called after migration and may raise exceptions on failure.

Security Notes

• The tool does not make any network requests. All operations are local file reads/writes with optional user-provided code execution via --transforms / --validate (evaluate with caution).
• Placeholder substitution is regex-based and does not execute shell commands.

License

MIT © 2024 ConfigMigrator Contributors