Building Scalable APIs: Best Practices from Production

Introduction

Over the past few years, we've built APIs that handle millions of requests per day. Here are the key practices that have helped us build reliable, scalable, and maintainable APIs.

1. Design for Scale from Day One

Don't wait until you hit performance issues. Design your API architecture with scale in mind:

• Stateless design: APIs should be stateless to enable horizontal scaling
• Idempotency: Make operations idempotent to handle retries safely
• Versioning: Version your API from v1 to allow breaking changes
• Pagination: Always paginate list endpoints, even if you don't need it now

2. Caching Strategy

Effective caching can reduce database load by 80%+:

• Cache frequently accessed data: User profiles, configuration, reference data
• Use appropriate TTL: Short TTL for dynamic data, longer for static data
• Cache invalidation: Implement smart invalidation strategies (tag-based, time-based)
• CDN for static content: Serve images, documents through CDN

3. Rate Limiting

Protect your API from abuse and ensure fair usage:

• Per-user rate limits: Different limits for different user tiers
• Per-endpoint limits: Stricter limits for expensive operations
• Sliding window: More accurate than fixed window for burst traffic
• Clear error messages: Tell users when and why they're rate limited

4. Monitoring & Observability

You can't optimize what you can't measure:

• Request metrics: Track response times, error rates, throughput
• Business metrics: Track API usage patterns, popular endpoints
• Error tracking: Log and alert on errors, especially 5xx errors
• Distributed tracing: Use tools like Jaeger or Datadog APM

5. Database Optimization

Database is often the bottleneck:

• Indexes: Proper indexes on frequently queried fields
• Query optimization: Avoid N+1 queries, use joins efficiently
• Connection pooling: Reuse database connections
• Read replicas: Distribute read load across replicas
• Database sharding: For very large datasets, consider sharding

6. Error Handling

Good error handling improves developer experience:

• Consistent error format: Use standard error response structure
• Meaningful error messages: Help developers debug issues
• Proper HTTP status codes: Use correct status codes (400, 401, 403, 404, 500)
• Error logging: Log errors with context for debugging

7. Security Best Practices

• Authentication: Use JWT tokens with proper expiration
• Authorization: Implement role-based access control (RBAC)
• Input validation: Validate and sanitize all inputs
• HTTPS only: Never expose APIs over HTTP
• API keys: Rotate keys regularly, use different keys for different environments

Real-World Example

One of our APIs handles 10M+ requests per day. Here's what we did:

• Implemented Redis caching layer — reduced database queries by 85%
• Added rate limiting — prevented abuse and improved stability
• Optimized database queries — reduced average response time from 200ms to 50ms
• Added monitoring — caught issues before they became problems
• Implemented circuit breakers — prevented cascading failures

Result: 99.9% uptime, sub-100ms average response time, zero security incidents.