Environment configuration and multi-environment management

Basic Concepts of Environment Configuration

Environment configuration is an essential aspect of Express application development. The requirements for development, testing, and production environments vary, such as database connections, API keys, and log levels. Proper configuration ensures seamless operation across different environments.

// Basic environment variable example
const port = process.env.PORT || 3000;
const dbUrl = process.env.DB_URL || 'mongodb://localhost:27017/dev_db';

Managing Environment Variables with dotenv

The dotenv package loads environment variables from a .env file into process.env. First, install it:

npm install dotenv

Create a .env file:

PORT=3000
DB_URL=mongodb://localhost:27017/prod_db
API_KEY=your_api_key_here

Load the configuration in your application:

require('dotenv').config();

const express = require('express');
const app = express();

app.listen(process.env.PORT, () => {
  console.log(`Server running on port ${process.env.PORT}`);
});

Multi-Environment Configuration Strategies

Configuration File Approach

Create a config directory with environment-specific files:

/config
  ├── default.js
  ├── development.js
  ├── test.js
  └── production.js

default.js contains common configurations:

module.exports = {
  logLevel: 'info',
  timeout: 5000
};

development.js extends the default configuration:

const config = require('./default');

module.exports = Object.assign({}, config, {
  dbUrl: 'mongodb://localhost:27017/dev_db',
  debug: true
});

Environment Variable Override Approach

Specify the environment using NODE_ENV:

NODE_ENV=production node app.js

Dynamically load configurations in the code:

const env = process.env.NODE_ENV || 'development';
const config = require(`./config/${env}`);

app.set('dbUrl', config.dbUrl);

Advanced Configuration Techniques

Configuration Validation

Use joi to validate environment variables:

const Joi = require('joi');

const schema = Joi.object({
  PORT: Joi.number().required(),
  DB_URL: Joi.string().uri().required()
});

const { error, value } = schema.validate(process.env);

if (error) {
  throw new Error(`Configuration validation failed: ${error.message}`);
}

Handling Sensitive Information

For sensitive data, consider encryption or key management services:

const { SecretManagerServiceClient } = require('@google-cloud/secret-manager');
const client = new SecretManagerServiceClient();

async function getSecret(secretName) {
  const [version] = await client.accessSecretVersion({
    name: secretName
  });
  return version.payload.data.toString();
}

Environment-Specific Middleware

Load different middleware based on the environment:

if (process.env.NODE_ENV === 'development') {
  app.use(require('morgan')('dev'));
  app.use(require('errorhandler')());
}

if (process.env.NODE_ENV === 'production') {
  app.use(require('compression')());
  app.use(require('helmet')());
}

Special Handling for Test Environments

Test environments may require mocked services:

if (process.env.NODE_ENV === 'test') {
  const { setupMockDatabase } = require('./test/mocks');
  setupMockDatabase();
  
  // Disable logs to avoid interfering with test output
  app.set('logger', { info: () => {}, error: () => {} });
}

Deployment Configuration Practices

Docker Environment Variables

Pass environment variables in Docker:

FROM node:14

ENV NODE_ENV=production

COPY . .
RUN npm install

CMD ["node", "app.js"]

Override when starting the container:

docker run -e "DB_URL=mongodb://prod-db:27017/app" my-app

Kubernetes Configuration

Use ConfigMap and Secret:

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  NODE_ENV: "production"
  LOG_LEVEL: "info"

Hot Reload for Configuration

Enable configuration hot reload in development:

const fs = require('fs');
const path = require('path');

let config = require('./config/development');

fs.watch(path.join(__dirname, 'config/development.js'), () => {
  delete require.cache[require.resolve('./config/development')];
  config = require('./config/development');
  console.log('Configuration reloaded');
});

Cross-Team Collaboration Configuration

Use configuration templates to help new team members get started quickly:

.env.example

Example content:

# Application configuration
PORT=3000

# Database configuration
DB_URL=mongodb://localhost:27017/dev_db

# Third-party API
API_KEY=your_api_key_here

Version Control for Configuration

Separate sensitive information from configuration. Recommended .gitignore:

# Ignore local environment files
.env
*.local.env

# Ignore sensitive configurations
config/local*.js

Commit example files:

.env.example
config/example.js