Scenario

A microservices application uses two YAML configuration files: a base file with defaults and an overrides file for environment-specific settings.

Task

Write a Python script named merge_config.py in /home/interview/ that accepts two YAML file paths as command-line arguments (base and overrides), performs a deep merge, then extracts the database section and saves it to /home/interview/database_config.json.

The script will be executed as: python3 /home/interview/merge_config.py /home/interview/base.yaml /home/interview/overrides.yaml

Note: The PyYAML library is already installed.

Example

Expected output format in /home/interview/database_config.json:

{
  "primary": {
    "host": "prod-db-primary.example.com",
    "port": 5432,
    ...
  },
  "replica": {
    ...
  }
}

Step 1: Create the Python script

nano /home/interview/merge_config.py

Write a script that deep merges YAML files and extracts the database section:

import yaml
import json
import sys

def deep_merge(base, override):
    """Recursively merge override into base"""
    result = base.copy()
    
    for key, value in override.items():
        if key in result and isinstance(result[key], dict) and isinstance(value, dict):
            result[key] = deep_merge(result[key], value)
        else:
            result[key] = value
    
    return result

# Load base configuration
with open(sys.argv[1], 'r') as f:
    base_config = yaml.safe_load(f)

# Load overrides configuration
with open(sys.argv[2], 'r') as f:
    overrides_config = yaml.safe_load(f)

# Deep merge configurations
merged_config = deep_merge(base_config, overrides_config)

# Extract database section
database_config = merged_config['database']

# Save to JSON
with open('/home/interview/database_config.json', 'w') as f:
    json.dump(database_config, f, indent=2)

print("Configuration merged and database section extracted")

The deep_merge function recursively merges nested dictionaries, preserving values that only exist in the base config while applying overrides.

Step 2: Run the script

python3 /home/interview/merge_config.py /home/interview/base.yaml /home/interview/overrides.yaml

Step 3: Verify the output

cat /home/interview/database_config.json

The output should show the database configuration with production values merged in (e.g., prod-db-primary.example.com for primary host, max_connections: 50).