What's the most cost-effective way to protect public endpoints using an API gateway with rate limiting?

The most cost-effective approach is usually:

1) Put a managed API gateway in front of the public endpoints

Use a cloud-native gateway instead of self-hosting one unless you already have strong infra reasons.

Examples:

• AWS: API Gateway + AWS WAF
• GCP: API Gateway / Apigee + Cloud Armor
• Azure: API Management + Azure DDoS Protection / WAF
• Cloudflare: Gateway/Workers + Rate Limiting + WAF

Why this is cost-effective:

• Minimal ops overhead
• Scales automatically
• Lets you enforce rate limits before traffic reaches your app
• Usually cheaper than overprovisioning backend capacity to absorb abuse

2) Enforce rate limiting at the edge/gateway, not in the app

Set limits based on:

• Per API key / client ID
• Per IP for unauthenticated traffic
• Per user/account if authenticated
• Optional: per route (e.g., stricter for login, search, expensive reports)

Recommended pattern:

• Burst limit: short spikes allowed
• Sustained limit: lower long-term cap

Example:

• 20 req/sec burst, 1000 req/min sustained for normal clients
• Much lower for sensitive endpoints like login or OTP requests

3) Use a tiered policy

This is often the cheapest and most practical:

• Anonymous/public: very strict limits
• Authenticated free tier: moderate limits
• Paid/partner tier: higher limits
• Internal/service accounts: separate higher quotas

This prevents one policy from being too generous or too restrictive.

4) Add cheap controls before expensive ones

A cost-effective stack is:

1. CDN / edge protection (blocks junk early)
2. WAF for common abuse patterns
3. Rate limiting at gateway
4. Application-level checks only for business-specific logic

This reduces traffic reaching your app and database, which saves more than the gateway costs.

5) Prefer token bucket/leaky bucket over heavy custom logic

Most gateways support standard algorithms. These are efficient and usually enough.

Use:

• Token bucket for burst tolerance
• Sliding window if you need tighter fairness
• Avoid custom per-request database lookups for rate limiting if possible

6) Cache and offload wherever possible

To reduce the need for strict limits:

• Cache GET endpoints
• Use CDN for static or semi-static responses
• Avoid expensive backend work on repeated requests
• Make unauthenticated endpoints as cheap as possible

7) Monitor and tune

Start with conservative limits and adjust using:

• Request volume
• 429 responses
• Error rates
• Client feedback
• Bot/abuse patterns

If you want the shortest answer:

Use a managed API gateway with gateway-level rate limiting, plus WAF/CDN at the edge, and apply tiered per-client/per-IP limits. That’s usually the lowest-cost, lowest-ops way to protect public endpoints.

If you tell me your cloud/provider and traffic pattern, I can suggest a specific setup and example limits.