Configuration Management - Learning Module

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Environment-Based Configuration

The Same Code, Different Contexts

A core principle of modern software delivery is that the same build artifact runs in all environments. The difference between development, staging, and production isn't the code—it's the configuration. Database URLs change. API endpoints switch. Feature flags toggle. Security settings tighten.

This principle, central to twelve-factor apps and continuous delivery, separates concerns beautifully: code is versioned in source control, while configuration is managed per environment. But achieving this separation cleanly requires careful design.

Environment-based configuration done poorly leads to configuration sprawl, inconsistent environments, and the dreaded 'works in staging, breaks in production.' Done well, it creates predictable, debuggable deployments where environment differences are explicit and minimal.

What You Will Learn

By the end of this page, you will understand how to design configuration systems that adapt across environments while maximizing consistency. You'll learn environment detection, profile systems, environment variable conventions, and techniques for minimizing environment-specific divergence.

Understanding Deployment Environments

Before designing environment-based configuration, understand what environments exist and why they differ. Each environment serves distinct purposes, requiring specific configuration characteristics.

Common deployment environments:

Environment Purposes and Characteristics
Environment	Purpose	Configuration Characteristics
Development (Local)	Individual developer testing	Local services, debug logging, mock integrations, no SSL
CI/Test	Automated testing in pipelines	Ephemeral databases, test fixtures, fast timeouts
Staging/QA	Pre-production verification	Production-like, sanitized data, internal access only
Production	Serving real users	Real databases, minimal logging, full security, monitoring
Disaster Recovery	Failover capability	Mirrors production, different region, standby mode

What should differ between environments:

Not everything should vary. Identify the minimal set of differences necessary:

What Should Vary by Environment

•Connection Strings — Database URLs, API endpoints, message queue addresses differ per environment.
•Credentials — Each environment has its own secrets, never shared.
•Resource Limits — Pool sizes, timeouts, and concurrency limits scale with environment capacity.
•Logging Verbosity — Debug logging in development, minimal in production for performance.
•Security Settings — SSL requirements, CORS policies, rate limits adjust per environment.
•Feature Flags — New features may be enabled in staging but not production during rollout.

Minimize Differences

Every environment difference is a potential source of 'works here, fails there' bugs. Strive to minimize differences to only what's absolutely necessary. The more staging resembles production, the more reliable your deployments become.

Environment Detection Strategies

How does your application know which environment it's running in? This seemingly simple question has important implications for configuration loading.

Common detection approaches:

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// Pattern 1: Environment variable (most common)
type Environment = "development" | "test" | "staging" | "production";
 
function detectEnvironment(): Environment {
  const env = process.env.NODE_ENV || process.env.APP_ENV;
  
  switch (env?.toLowerCase()) {
    case "production":
    case "prod":
      return "production";
    case "staging":
    case "stage":
    case "qa":
      return "staging";
    case "test":
    case "ci":
      return "test";
    default:
      return "development";  // Safe default for local work
  }
}
 
// Pattern 2: Domain/hostname detection (for web apps)
function detectFromHostname(): Environment {
  const hostname = process.env.HOSTNAME || os.hostname();
  
  if (hostname.includes("prod") || hostname.endsWith(".com")) {
    return "production";
  }
  if (hostname.includes("staging") || hostname.includes("stage")) {
    return "staging";
  }
  return "development";
}
 
// Pattern 3: Configuration profile (explicit selection)
interface ConfigProfile {
  name: string;
  environment: Environment;
  configPath: string;
}
 
const PROFILES: Record<string, ConfigProfile> = {
  "dev": { name: "Development", environment: "development", configPath: "./config/dev.yaml" },
  "test": { name: "Test", environment: "test", configPath: "./config/test.yaml" },
  "staging": { name: "Staging", environment: "staging", configPath: "./config/staging.yaml" },
  "prod": { name: "Production", environment: "production", configPath: "./config/prod.yaml" },
};
 
function loadProfile(): ConfigProfile {
  const profileName = process.env.CONFIG_PROFILE || "dev";
  const profile = PROFILES[profileName];
  
  if (!profile) {
    throw new ConfigurationError(
      `Unknown config profile: ${profileName}. Valid: ${Object.keys(PROFILES).join(", ")}`
    );
  }
  
  return profile;
}

Detection Best Practices

•Use a single, explicit mechanism — Don't mix multiple detection methods. One source of truth prevents confusion.
•Default to safe — If detection fails, default to the safest (usually development) rather than the riskiest (production).
•Log the detected environment — At startup, log which environment was detected for debugging deployment issues.
•Fail on unknown values — In production, reject unknown environment values rather than falling back to defaults.
•Normalize input — Accept variations (prod, production, PRODUCTION) but store a canonical value internally.

Environment Variable Conventions

Environment variables are the primary mechanism for environment-specific configuration in containerized and cloud-native deployments. Following consistent conventions makes configuration predictable and discoverable.

Naming conventions:

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# Pattern: {APP_PREFIX}_{SECTION}_{SETTING}
 
# Application identification
APP_NAME=myservice
APP_VERSION=1.2.3
APP_ENV=production
 
# Database configuration
APP_DATABASE_HOST=db.production.internal
APP_DATABASE_PORT=5432
APP_DATABASE_NAME=myservice
APP_DATABASE_USERNAME=app_user
APP_DATABASE_PASSWORD=<from-secrets-manager>
APP_DATABASE_POOL_SIZE=20
APP_DATABASE_CONNECTION_TIMEOUT_MS=30000
 
# HTTP server configuration
APP_SERVER_HTTP_PORT=8080
APP_SERVER_HTTP_HOST=0.0.0.0
APP_SERVER_HTTP_REQUEST_TIMEOUT_MS=60000
 
# Feature flags
APP_FEATURE_NEW_CHECKOUT=true
APP_FEATURE_DARK_MODE=false
APP_FEATURE_BETA_API=true
 
# External services
APP_PAYMENTS_API_URL=https://api.payments.com/v2
APP_PAYMENTS_API_TIMEOUT_MS=10000
APP_ANALYTICS_ENDPOINT=https://analytics.internal/ingest

Mapping environment variables to configuration:

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// Type-safe environment variable reader
class EnvReader {
  constructor(private prefix: string = "APP") {}
  
  getString(key: string, required: boolean = true): string | undefined {
    const envKey = `${this.prefix}_${key}`;
    const value = process.env[envKey];
    
    if (required && !value) {
      throw new ConfigurationError(`Required env var missing: ${envKey}`);
    }
    return value;
  }
  
  getNumber(key: string, defaultValue?: number): number {
    const value = this.getString(key, defaultValue === undefined);
    if (!value) return defaultValue!;
    
    const num = parseInt(value, 10);
    if (isNaN(num)) {
      throw new ConfigurationError(`Invalid number for ${key}: ${value}`);
    }
    return num;
  }
  
  getBoolean(key: string, defaultValue?: boolean): boolean {
    const value = this.getString(key, defaultValue === undefined);
    if (!value) return defaultValue!;
    
    const lower = value.toLowerCase();
    if (lower === "true" || lower === "1" || lower === "yes") return true;
    if (lower === "false" || lower === "0" || lower === "no") return false;
    
    throw new ConfigurationError(`Invalid boolean for ${key}: ${value}`);
  }
  
  getEnum<T extends string>(key: string, validValues: readonly T[]): T {
    const value = this.getString(key) as T;
    
    if (!validValues.includes(value)) {
      throw new ConfigurationError(
        `Invalid value for ${key}: ${value}. Valid: ${validValues.join(", ")}`
      );
    }
    return value;
  }
}
 
// Usage
const env = new EnvReader("APP");
 
const databaseConfig: DatabaseConfig = {
  host: env.getString("DATABASE_HOST")!,
  port: env.getNumber("DATABASE_PORT", 5432),
  database: env.getString("DATABASE_NAME")!,
  username: env.getString("DATABASE_USERNAME")!,
  password: env.getString("DATABASE_PASSWORD")!,
  poolSize: env.getNumber("DATABASE_POOL_SIZE", 10),
  connectionTimeoutMs: env.getNumber("DATABASE_CONNECTION_TIMEOUT_MS", 30000),
};

Documentation Generation

Generate documentation of all expected environment variables from your configuration code. This prevents drift between what the code expects and what operators know to configure. Some tools can generate .env.example files automatically from TypeScript configuration interfaces.

Configuration Profile Systems

A configuration profile is a named set of configuration overrides. Profiles allow loading different configuration bundles without changing individual environment variables—useful for testing specific scenarios or maintaining multiple deployment variants.

Profile-based configuration loading:

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// config/
// ├── base.yaml           <- Shared across all profiles
// ├── profiles/
// │   ├── development.yaml
// │   ├── test.yaml
// │   ├── staging.yaml
// │   ├── production.yaml
// │   └── performance-test.yaml  <- Special-purpose profile
// └── local.yaml          <- Local overrides (gitignored)
 
interface ConfigurationLoader {
  loadProfile(profileName: string): Promise<AppConfig>;
}
 
class YamlConfigurationLoader implements ConfigurationLoader {
  async loadProfile(profileName: string): Promise<AppConfig> {
    // 1. Load base configuration
    const base = await this.loadYaml("config/base.yaml");
    
    // 2. Load profile-specific overrides
    const profilePath = `config/profiles/${profileName}.yaml`;
    const profile = await this.loadYaml(profilePath);
    
    // 3. Load local overrides if present (for developer customization)
    const local = await this.loadYamlOptional("config/local.yaml");
    
    // 4. Merge in order: base < profile < local
    const merged = this.deepMerge(base, profile, local);
    
    // 5. Apply environment variable overrides (highest precedence)
    const withEnv = this.applyEnvironmentOverrides(merged);
    
    // 6. Validate and freeze
    return this.validateAndFreeze(withEnv);
  }
}
 
// Profile switching at runtime
const profile = process.env.CONFIG_PROFILE || "development";
const config = await loader.loadProfile(profile);
 
console.log(`Loaded configuration profile: ${profile}`);

Profile inheritance and composition:

Profiles can inherit from each other, reducing duplication:

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# config/profiles/base-cloud.yaml
# Shared configuration for all cloud environments
aws:
  region: us-east-1
  
server:
  http:
    port: 8080
    host: "0.0.0.0"
    
database:
  pool:
    minConnections: 5
    maxConnections: 20
    
logging:
  format: json
  
---
# config/profiles/staging.yaml
extends: base-cloud
 
environment: staging
 
database:
  host: staging-db.internal
  
features:
  enableBetaFeatures: true
  enableDebugEndpoints: true
  
---
# config/profiles/production.yaml  
extends: base-cloud
 
environment: production
 
database:
  host: prod-db.internal
  pool:
    maxConnections: 50  # Override base-cloud
    
features:
  enableBetaFeatures: false
  enableDebugEndpoints: false
  
logging:
  level: info  # Less verbose in production

Profile vs. Environment Variables

Use profiles for structured, related configuration changes (like switching from local dev to cloud staging). Use environment variables for individual values that may differ even within the same profile (like database passwords, which differ per-deployment even in production).

Handling Secrets Across Environments

Secrets—passwords, API keys, tokens—require special handling. Unlike regular configuration, secrets must be protected from exposure in logs, version control, and error messages.

Environment-specific secret management:

Secret Management by Environment
Environment	Recommended Approach	Example
Development	Local .env file (gitignored)	DB_PASSWORD=devpassword
CI/Test	Pipeline secret injection	GitHub Secrets, GitLab CI Variables
Staging	Secrets manager with limited access	AWS Secrets Manager, HashiCorp Vault
Production	Secrets manager with audit logging	AWS Secrets Manager + CloudTrail, Vault + Audit

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// Don't store secrets in configuration objects - store references
interface DatabaseConfig {
  host: string;
  port: number;
  database: string;
  // Reference to secret, not the secret itself
  credentialsRef: SecretReference;
}
 
interface SecretReference {
  source: "env" | "file" | "vault" | "aws-secrets-manager";
  key: string;
}
 
// Secret resolver that fetches actual values at runtime
interface SecretsResolver {
  resolve(ref: SecretReference): Promise<string>;
}
 
class CompositeSecretsResolver implements SecretsResolver {
  constructor(private resolvers: Map<string, SecretsResolver>) {}
  
  async resolve(ref: SecretReference): Promise<string> {
    const resolver = this.resolvers.get(ref.source);
    if (!resolver) {
      throw new ConfigurationError(`Unknown secret source: ${ref.source}`);
    }
    return resolver.resolve(ref);
  }
}
 
// Environment-specific resolver configuration
function createSecretsResolver(environment: Environment): SecretsResolver {
  const resolvers = new Map<string, SecretsResolver>();
  
  // All environments can use environment variables
  resolvers.set("env", new EnvVarSecretsResolver());
  
  if (environment === "development") {
    // Dev can use local files
    resolvers.set("file", new FileSecretsResolver("./secrets"));
  } else {
    // Non-dev uses secrets manager
    resolvers.set("aws-secrets-manager", new AwsSecretsManagerResolver());
    resolvers.set("vault", new VaultSecretsResolver());
  }
  
  return new CompositeSecretsResolver(resolvers);
}
 
// Usage at application startup
const secretsResolver = createSecretsResolver(environment);
const dbPassword = await secretsResolver.resolve(config.database.credentialsRef);

Never Log Secrets

Never log configuration that might contain secrets. When logging configuration at startup, redact or omit any fields that contain sensitive data. Better yet, don't put secrets in the config object at all—keep them in a separate SecretsResolver that provides values on demand.

Maximizing Environment Parity

Environment parity means keeping development, staging, and production as similar as possible. Differences cause bugs that only appear in production—the worst kind of bugs.

Sources of environment drift:

Common Parity Violations

•Different Backing Services — Using SQLite locally vs PostgreSQL in production causes subtle SQL compatibility issues.
•Different Versions — Running Node 18 locally but Node 20 in production causes runtime behavior differences.
•Different Timeouts — Aggressive timeouts in tests hide latency issues that cause production failures.
•Missing Integrations — Mocking external services locally means integration issues surface only in production.
•Different Data Scale — Testing with 10 rows locally works, but 10 million rows in production reveal O(n²) issues.

Strategies for maintaining parity:

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// Strategy 1: Use the same backing services everywhere
// Docker Compose for local development matches production stack
 
// docker-compose.dev.yml
// services:
//   postgres:
//     image: postgres:15  # Same version as production
//   redis:
//     image: redis:7      # Same version as production
//   localstack:
//     image: localstack/localstack  # AWS services locally
 
// Strategy 2: Minimize environment-specific code paths
enum Environment {
  Development = "development",
  Staging = "staging",
  Production = "production",
}
 
// ❌ BAD: Environment-specific logic scattered in business code
function processPayment(payment: Payment): Result {
  if (environment === Environment.Development) {
    // Completely different code path in dev
    return mockPaymentProcessor.process(payment);
  } else {
    return realPaymentProcessor.process(payment);
  }
}
 
// ✅ GOOD: Same code path, environment-specific configuration/dependencies
interface PaymentProcessor {
  process(payment: Payment): Promise<Result>;
}
 
// Injected at startup based on environment
class PaymentService {
  constructor(private processor: PaymentProcessor) {}
  
  process(payment: Payment): Promise<Result> {
    // Same code path in all environments
    return this.processor.process(payment);
  }
}
 
// Strategy 3: Configuration that fails in non-production
// If a production-only integration isn't configured, fail early
function validateProductionReadiness(config: AppConfig): void {
  if (config.environment === "production") {
    if (!config.monitoring.datadogApiKey) {
      throw new ConfigurationError(
        "Production requires monitoring configuration"
      );
    }
    if (!config.alerting.pagerDutyServiceKey) {
      throw new ConfigurationError(
        "Production requires alerting configuration"
      );
    }
  }
}

Production-Like Local Development

Invest in making local development production-like. Docker Compose, local Kubernetes (Kind, Minikube), or cloud-based dev environments (Gitpod, Codespaces) can run the full production stack locally. The closer local development matches production, the fewer surprises at deployment time.

Environment-Specific Validation

Different environments have different configuration requirements. Production has stricter requirements than development—SSL must be enabled, logging must be configured, monitoring must be present.

Tiered validation approach:

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// Validation rules by environment
interface ConfigValidationRule {
  description: string;
  environments: Environment[];
  validate: (config: AppConfig) => ValidationResult;
}
 
const VALIDATION_RULES: ConfigValidationRule[] = [
  // Rules for all environments
  {
    description: "Database connection must be configured",
    environments: ["development", "staging", "production"],
    validate: (config) => {
      if (!config.database.host) {
        return { valid: false, error: "Database host is required" };
      }
      return { valid: true };
    },
  },
  
  // Production-only rules
  {
    description: "SSL must be enabled in production",
    environments: ["production"],
    validate: (config) => {
      if (!config.server.tls?.enabled) {
        return { valid: false, error: "TLS must be enabled in production" };
      }
      return { valid: true };
    },
  },
  {
    description: "Debug logging forbidden in production",
    environments: ["production"],
    validate: (config) => {
      if (config.logging.level === "debug" || config.logging.level === "trace") {
        return { 
          valid: false, 
          error: "Debug/trace logging not allowed in production" 
        };
      }
      return { valid: true };
    },
  },
  {
    description: "Monitoring must be configured in production",
    environments: ["production"],
    validate: (config) => {
      if (!config.monitoring.enabled || !config.monitoring.endpoint) {
        return { valid: false, error: "Monitoring is required in production" };
      }
      return { valid: true };
    },
  },
  
  // Staging + Production rules
  {
    description: "Connection pooling must be enabled",
    environments: ["staging", "production"],
    validate: (config) => {
      if (config.database.pool.maxConnections < 5) {
        return { 
          valid: false, 
          error: "Pool size too small for staging/production" 
        };
      }
      return { valid: true };
    },
  },
  
  // Development warnings (non-blocking)
  {
    description: "Consider enabling SSL even in development",
    environments: ["development"],
    validate: (config) => {
      if (!config.server.tls?.enabled) {
        return { 
          valid: true, 
          warning: "Consider enabling TLS in development for parity" 
        };
      }
      return { valid: true };
    },
  },
];
 
function validateConfiguration(
  config: AppConfig, 
  environment: Environment
): ConfigValidationResult {
  const errors: string[] = [];
  const warnings: string[] = [];
  
  for (const rule of VALIDATION_RULES) {
    if (!rule.environments.includes(environment)) continue;
    
    const result = rule.validate(config);
    if (!result.valid && result.error) {
      errors.push(`${rule.description}: ${result.error}`);
    }
    if (result.warning) {
      warnings.push(`${rule.description}: ${result.warning}`);
    }
  }
  
  return {
    valid: errors.length === 0,
    errors,
    warnings,
  };
}

Fail Fast in Production

In production, configuration validation failures should prevent application startup—it's better to not start than to start with invalid configuration. In development, you might allow warnings or graceful degradation to avoid blocking developer productivity.

Testing Environment-Specific Configuration

Configuration code requires testing like any other code. Test that configuration loads correctly, validates properly, and merges as expected across environments.

Configuration testing strategies:

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// Test 1: All environment configurations load successfully
describe("Configuration Loading", () => {
  const environments = ["development", "test", "staging", "production"];
  
  for (const env of environments) {
    it(`should load ${env} configuration without errors`, async () => {
      // Set minimal required environment variables
      process.env.APP_ENV = env;
      process.env.DATABASE_PASSWORD = "test-password";
      
      const config = await loadConfiguration();
      
      expect(config).toBeDefined();
      expect(config.environment).toBe(env);
    });
  }
});
 
// Test 2: Configuration validation catches issues
describe("Configuration Validation", () => {
  it("should reject production config without TLS", () => {
    const config: AppConfig = {
      environment: "production",
      server: { tls: { enabled: false } },
      // ... other config
    };
    
    const result = validateConfiguration(config, "production");
    
    expect(result.valid).toBe(false);
    expect(result.errors).toContain(expect.stringContaining("TLS"));
  });
  
  it("should allow development config without TLS", () => {
    const config: AppConfig = {
      environment: "development",
      server: { tls: { enabled: false } },
      // ... other config
    };
    
    const result = validateConfiguration(config, "development");
    
    expect(result.valid).toBe(true);
  });
});
 
// Test 3: Environment variable overrides work correctly
describe("Environment Variable Overrides", () => {
  it("should override config file values with env vars", async () => {
    // Config file has port: 3000
    process.env.APP_SERVER_PORT = "9000";
    
    const config = await loadConfiguration();
    
    expect(config.server.port).toBe(9000);
  });
  
  it("should use config file value when env var not set", async () => {
    delete process.env.APP_SERVER_PORT;
    
    const config = await loadConfiguration();
    
    expect(config.server.port).toBe(3000);  // From config file
  });
});
 
// Test 4: Secrets are not exposed
describe("Secret Handling", () => {
  it("should not include secrets in serialized config", () => {
    const config = createTestConfig({
      database: {
        credentialsRef: { source: "env", key: "DB_PASSWORD" }
      }
    });
    
    const serialized = JSON.stringify(config);
    
    expect(serialized).not.toContain("password");
    expect(serialized).not.toContain("secret");
  });
  
  it("should mask secrets in toString/logging output", () => {
    const config = createTestConfig();
    
    const logged = config.toLoggableString();
    
    expect(logged).toContain("[REDACTED]");
    expect(logged).not.toContain("actual-password-value");
  });
});

Summary: Environment-Based Configuration

Environment-based configuration enables the same code to run differently across deployment contexts. Well-designed environment configuration maximizes parity while accommodating necessary differences, catches configuration errors before they cause production incidents, and supports secure secret management.

Key Takeaways

•Minimize environment differences — Every difference is a potential bug. Only vary what must vary.
•Use consistent detection — One mechanism for determining environment, logged at startup.
•Follow naming conventions — Predictable environment variable names enable discovery and tooling.
•Leverage profiles — Named configuration bundles for complex, related changes.
•Handle secrets separately — Reference-based secret management, never plain text in config.
•Maximize parity — Same backing services, same versions, same code paths across environments.
•Validate by environment — Stricter rules for production, warnings for development.
•Test configuration code — Configuration loading, validation, and override behavior need tests.

What's next:

Even perfect configuration is useless if it's incorrect. The next page explores configuration validation—how to catch invalid configuration at application startup before it causes runtime failures. We'll cover schema validation, dependency validation, and fail-fast startup patterns.

Page Complete

You now understand how to design configuration systems that adapt across deployment environments while maintaining parity and security. Next, we'll ensure that configuration is valid before your application starts accepting traffic.