Microservices Architecture: When and How

The microservices hype cycle has matured. After a decade of "microservices all the things," the industry now recognizes that microservices solve specific problems while introducing significant complexity. At Acceli, we've architected both monolithic and microservices systems for clients ranging from startups to enterprises. This article synthesizes lessons from successful and failed migrations, focusing on the decision framework that separates successful microservices architectures from distributed monoliths.

When Microservices Make Sense

Most applications don't need microservices. A well-designed monolith handles millions of users efficiently with far less operational complexity. Microservices make sense when facing specific scaling challenges that monoliths genuinely cannot solve.

Team Scaling and Organizational Autonomy

When development teams exceed 15-20 engineers, coordinating deployments and managing merge conflicts in a monolithic codebase becomes painful. A fintech client with 45 developers was deploying once per week due to coordination overhead. Migrating to microservices enabled 8 autonomous teams deploying independently 50+ times per week.

Critical success factor: align services with team boundaries, not technical layers. Services owned by single teams move faster than services requiring cross-team coordination. One team owns the service from database to API to deployment.

Heterogeneous Scaling Requirements

When different parts of your application have dramatically different resource needs, microservices enable independent scaling. An e-commerce client's image processing service needed 16GB RAM and 8 CPUs, while most services ran efficiently on 512MB containers. With a monolith, they over-provisioned all instances. With microservices, infrastructure costs dropped 60%.

Warning: if all components scale similarly, microservices add overhead without benefit. Profile carefully before assuming you need independent scaling. Most applications have uniform scaling patterns.

Technology Diversity Requirements

Occasionally, specific services benefit from different technology stacks. A real-time analytics service written in Go processed events 10x faster than Node.js alternatives. A machine learning service needed Python for model serving. Microservices enabled using optimal technology for each component.

Caution: technology diversity creates hiring and maintenance challenges. Only introduce new languages when the performance or ecosystem benefits clearly justify the added complexity. One client's "polyglot" architecture with 5 languages became unmaintainable.

The Hidden Costs

Microservices move complexity from the codebase to the infrastructure and operational layers. Teams often underestimate these costs, leading to failed migrations and expensive operational overhead.

Distributed System Debugging Complexity

When a monolith fails, you have stack traces and logs in one place. When a microservices request fails, you're tracking it across 5-10 services with network boundaries obscuring causality. For a logistics platform, implementing distributed tracing (OpenTelemetry + Tempo) and correlation IDs required 3 months of engineering time and ongoing operational overhead.

Essential tooling: distributed tracing (Jaeger, Tempo), centralized logging (ELK, Loki), and service mesh for observability (Istio, Linkerd). Budget $100K+ annually for observability infrastructure in production microservices systems. Without this, debugging production issues becomes nearly impossible.

Network Reliability Becomes Your Problem

In-process function calls don't fail. Network calls fail constantly. A payment processing system experienced 0.1% network error rates, translating to 1,000 failed payments per million requests. We implemented circuit breakers, retries with exponential backoff, and idempotency patterns to achieve acceptable reliability.

Required patterns: circuit breakers (Hystrix, resilience4j), timeout and retry strategies, idempotency for write operations, graceful degradation, and bulkheads to isolate failures. These patterns are complex to implement correctly and require ongoing tuning based on production behavior.

Data Consistency Across Services

Monoliths use database transactions for consistency. Microservices require distributed transaction patterns (Saga, eventual consistency) which are conceptually complex and difficult to test. For an order processing system, implementing the Saga pattern for order fulfillment across 4 services took 6 weeks versus 2 days for the equivalent monolithic transaction.

Trade-off: microservices force you to accept eventual consistency in most cases. This has profound implications for business logic and requires careful UX design to hide consistency delays from users. "Your order is processing" instead of immediate confirmation.

Proven Migration Strategies

Migrating from monolith to microservices requires careful sequencing. Attempting a "big bang" rewrite has a near 100% failure rate in our experience.

Strangler Fig Pattern

Incrementally extract services from the monolith while routing new functionality to microservices. For a SaaS platform, we extracted services over 18 months: month 1-3: authentication service, month 4-6: notification service, month 7-12: core business logic services, month 13-18: legacy feature migration.

Critical: use API gateway (Kong, Ambassador) to route requests between monolith and new services. This enables gradual migration without forcing clients to know about architecture changes. Users see one system while you're running two behind the scenes.

Start With the Edges

Extract stateless, low-dependency services first (email, notifications, reports). These have minimal blast radius if migrations go wrong. For a healthcare platform, we extracted the notification service first, which had no database dependencies and simple API contracts. This built team confidence before tackling complex domain services.

Anti-pattern: extracting core domain services first maximizes risk and complexity. Build operational maturity with simpler services before attempting complex extractions. Learn distributed tracing, monitoring, and deployment patterns on low-risk services.

Technology Stack Recommendations

Kubernetes is the standard for microservices orchestration, but it's complex. For teams under 10 engineers, consider managed platforms (AWS ECS, Google Cloud Run, Azure Container Apps) that abstract Kubernetes complexity while providing orchestration benefits.

A 5-person startup chose Cloud Run over Kubernetes and deployed their first microservices in 2 weeks instead of 2 months. They scaled to 50+ services before Kubernetes complexity became justified. Don't over-engineer your infrastructure before you need it.

Conclusion

Microservices solve specific problems: organizational scaling, independent deployment, and heterogeneous requirements. They're not a default choice. For most applications under 10 engineers or 100K users, a well-designed monolith is faster to build and simpler to operate. If you need microservices, migrate incrementally and invest heavily in observability. Total cost of ownership is typically 2-3x higher than monoliths—ensure business benefits justify these costs.