To keep your system running smoothly when millions of users access it at the same time, a Software Architect needs to consider many factors.
Below is a comprehensive checklist of bottlenecks and optimization solutions to ensure your system is always ready for high traffic.

1. Bottleneck from monolith architecture

All logic and resources are bundled together → difficult to scale
Solutions:

  • Switch to microservices
  • Make services stateless to allow horizontal scaling
  • Add an API Gateway (rate-limiting, circuit breaker)
  • Use a service mesh (Istio, Linkerd) if observability is needed

2. DB bottleneck due to too many direct queries

1 million users can generate tens of millions of DB queries
Solutions:

  • Use a connection pool (HikariCP, PgBouncer)
  • Read/Write splitting (Master-Slave)
  • Caching layer (Redis/Memcached) for hot data
  • Shard or partition large tables

3. Heavy tasks included in the main request flow

Sending emails, logging, image processing, etc. in the sync flow slows things down
Solutions:

  • Use a message queue (Kafka, RabbitMQ, Redis Streams)
  • Producers push jobs, consumers process asynchronously
  • Retry logic with delay and dead-letter queues

4. Missing or poorly implemented caching

Querying data on every page load overwhelms the system
Solutions:

  • Multi-layer cache: CDN → Redis → Local Cache
  • Use correct TTL and cache invalidation
  • Dynamic cache keys: user:{id}, homepage:{lang}
  • Use cache-aside instead of write-through for frequently changing data

5. Unoptimized Frontend and APIs

The frontend spams too many APIs, large payloads, and lacks lazy loading
Solutions:

  • Use GraphQL or Backend-for-Frontend (BFF) to consolidate APIs
  • Enable GZIP, HTTP/2, and use CDN for static assets
  • Debounce input and paginate all lists
  • Use smart prefetching instead of loading everything at once

6. Infrastructure doesn’t auto-scale

Traffic spikes, but the app doesn’t scale accordingly
Solutions:

  • Deploy on Kubernetes (HPA, VPA)
  • Use autoscaling services like EC2, Cloud Run, Fargate
  • Layer 7 Load Balancer (to block DDoS, smart traffic routing)