Azure APIM: Lessons from Handling Millions of Requests

Over the past three years, I've helped build and operate an Azure API Management instance that handles millions of requests daily. Here's what I wish I knew when we started.

The Promise and Reality

Azure APIM promises a lot: centralized API governance, developer portals, analytics, rate limiting, and more. Most of it delivers, but there are gotchas.

Key Lessons

1. Start with Policies, Not Code

APIM's policy system is surprisingly powerful. Before writing backend code for cross-cutting concerns, check if a policy can handle it:

This simple policy handles rate limiting and caching without touching your backend.

2. Named Values Are Your Friend

Hardcoding values in policies is a maintenance nightmare. Use Named Values for anything that might change:

API keys for external services

Backend URLs for different environments

Feature flags

3. Monitor Everything

APIM integrates with Application Insights, but you need to configure it thoughtfully. We track:

Request duration percentiles (p50, p95, p99)

Error rates by operation

Cache hit ratios

Backend health

4. Plan for Failures

Your APIM instance will have issues. We've seen:

Regional outages (use multi-region if critical)

Certificate expiration surprises

Policy deployment failures

Build runbooks for each scenario.

Performance Tips

A few things that made significant differences for us:

1. Enable response caching for GET requests where possible 2. Use backend circuit breakers to fail fast 3. Compress responses at the APIM level 4. Keep policies simple — complex transformations add latency

Conclusion

APIM is a powerful tool when used correctly. The key is understanding it's a platform, not a silver bullet. Invest time in learning its policy language and you'll be rewarded with a maintainable, scalable API gateway.

Questions? Drop a comment below.