Env Config Guidelines

Environment Configuration Guidelines

Core Principles

1. Fail fast - Validate configuration at startup
2. No secrets in code - All secrets from environment
3. Type safety - Parse and validate env vars
4. Defaults where safe - Sensible defaults for non-sensitive values
5. Documentation - Every variable documented

Environment Variable Naming

Naming Convention

# Format: SCOPE_CATEGORY_NAME

# Application config
APP_PORT={{DEFAULT_APP_PORT}}
APP_HOST={{DEFAULT_APP_HOST}}
APP_LOG_LEVEL=info

# Database
DATABASE_URL={{EXAMPLE_DATABASE_URL}}
DATABASE_POOL_SIZE=10
DATABASE_SSL_ENABLED=true

# External services
REDIS_URL=redis://{{DEFAULT_APP_HOST}}:{{DEFAULT_REDIS_PORT}}
STRIPE_API_KEY=sk_test_xxx
SENDGRID_API_KEY=SG.xxx

# Feature flags
FEATURE_NEW_DASHBOARD=true
FEATURE_BETA_API=false

Naming Rules

# Use SCREAMING_SNAKE_CASE
DATABASE_URL        # Good
databaseUrl         # Bad
database-url        # Bad

# Be specific
SMTP_HOST           # Good
HOST                # Bad - ambiguous

# Include units when relevant
CACHE_TTL_SECONDS=300
REQUEST_TIMEOUT_MS=5000
MAX_FILE_SIZE_MB=10

Configuration Loading

Type-Safe Configuration with Zod

import { z } from 'zod';

const envSchema = z.object({
  NODE_ENV: z.enum(['development', 'production', 'test']).default('development'),
  PORT: z.coerce.number().default({{DEFAULT_APP_PORT}}),
  HOST: z.string().default('{{DEFAULT_APP_HOST}}'),
  DATABASE_URL: z.string().url(),
  STRIPE_API_KEY: z.string().startsWith('sk_'),
  FEATURE_NEW_DASHBOARD: z.coerce.boolean().default(false),
});

function loadConfig() {
  const result = envSchema.safeParse(process.env);
  if (!result.success) {
    console.error('Invalid environment configuration:');
    console.error(result.error.format());
    process.exit(1);
  }
  return result.data;
}

export const config = loadConfig();
export type Config = z.infer<typeof envSchema>;

Environment Files

File Structure

.env                  # Default values (committed, no secrets)
.env.local            # Local overrides (not committed)
.env.development      # Development defaults
.env.production       # Production defaults (no secrets)
.env.test             # Test environment
.env.example          # Template with all variables documented

Loading Order

// Load in order, later files override earlier
// 1. .env
// 2. .env.local
// 3. .env.{NODE_ENV}
// 4. .env.{NODE_ENV}.local
// 5. Process environment (highest priority)

import { config } from 'dotenv';
import { expand } from 'dotenv-expand';

const env = process.env.NODE_ENV || 'development';

[
  '.env',
  '.env.local',
  `.env.${env}`,
  `.env.${env}.local`,
].forEach(file => {
  expand(config({ path: file, override: true }));
});

References

• Secrets Management - Gitignore rules, AWS SDK integration, secret rotation patterns
• Feature Flags - Simple and typed feature flag implementations
• Configuration Patterns - Per-environment config, config namespacing
• Configuration Validation - Required vs optional, startup validation, runtime checks, example file
• Known Gotchas - Boolean/number parsing, variable expansion, Docker environment

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