Microservices to ESA: Seeking Architectural Harmony

From SOA to Microservices to ESA: Seeking Architectural Harmony

March 07, 2025

Over the past two decades, I’ve watched the pendulum of software architecture swing—sometimes gracefully, sometimes chaotically—between centralized control and distributed freedom. Service-Oriented Architecture (SOA) promised us reusable business capabilities, but its rigidity left us wanting. Microservices burst onto the scene with agility and independence, yet they often traded simplicity for a tangle of complexity. Now, whispers of Essential Service Architecture (ESA) suggest a middle path—a way to balance the lessons of the past with the demands of the present. Let’s unpack this journey and see what ESA might mean for how we build systems.

SOA: The Monolith in Disguise

When SOA emerged in the early 2000s, it felt like a revelation. The idea was elegant: carve your system into services aligned with business functions—say, a "Customer Service" or an "Order Service"—and knit them together through a central nervous system, typically an Enterprise Service Bus (ESB). It was a noble attempt to tame the sprawling monoliths of the day, offering reusability and a clean separation of concerns.

But elegance in theory often meets reality’s rough edges. Those services, broad and ambitious, grew heavy with responsibility. Change one piece—like adding a new customer attribute—and you risked unsettling the whole. The ESB, meant to be a conduit, became a choke point, a single-threaded arbiter of every interaction. SOA’s promise of flexibility calcified into something rigid, a monolith wearing a service mask. Teams I worked with grew frustrated: SOA was too coarse, too coupled, too slow to adapt.

Microservices: Freedom’s Double-Edged Sword

Enter Microservices, the rebellious child of SOA, born in the mid-2010s amid the rise of cloud computing and DevOps. The pitch was irresistible: break those lumbering services into small, independent units, each doing one thing well. A "Payment Validation" service. An "Order Processing" service. Deploy them separately, scale them separately, let them chatter over lightweight APIs like REST or gRPC. Suddenly, teams could move fast, ship often, and embrace polyglot persistence—SQL here, NoSQL there.

I’ve seen microservices work wonders. A team I advised split a creaking e-commerce monolith into a dozen microservices, and within months, they were deploying daily instead of quarterly. But freedom comes at a cost, and microservices’ bill eventually arrives. The proliferation of services—what some call service sprawl—turns a system into a distributed puzzle. Each service needs its own database, its own deployment pipeline, its own monitoring. Those lightweight API calls multiply, and soon you’re drowning in network latency and retry logic. Data consistency? A nightmare of eventual reconciliation. I’ve watched architects sketch service diagrams that looked like constellations—beautiful, but bewildering.

Microservices traded SOA’s rigidity for complexity. It’s a trade worth making when you need agility and scale, but it’s not a universal cure. Too often, I’ve seen teams fragment their domains too finely, losing sight of the bigger picture. There had to be a better way.

ESA: A Pragmatic Synthesis

And so we arrive at Essential Service Architecture (ESA), a term I’ve started hearing more often in 2025. It’s not a radical departure but a thoughtful recalibration—a synthesis of SOA’s cohesion and Microservices’ autonomy. The core idea is to define services that are essential to the business, neither too broad nor too granular, and to orchestrate them with a blend of state management and event-driven design. It’s less about inventing something new and more about finding the right balance.

Avoiding the Sprawl

ESA takes a hard look at service boundaries. Microservices taught us that splitting everything into tiny pieces can backfire—do you really need separate services for "Order Validation" and "Order Persistence" if they’re always used together? ESA steps back and asks: what’s the smallest set of services that captures the essence of our domain? In an e-commerce system, you might end up with an "Order Fulfillment" service (handling orders and inventory) and a "Payment Processing" service—not a dozen microservices, not one SOA behemoth, but a handful of well-sized players. It’s the Goldilocks principle applied to architecture.

Cutting the Chatter

One of Microservices’ hidden taxes is the API explosion—services pinging each other incessantly, racking up latency and failure points. ESA leans on events to slim this down. Instead of "Order Service" polling "Inventory Service" with REST calls, an "OrderPlaced" event triggers the next step. Services listen, react, and move on. Fewer direct calls, less network strain. I’ve seen this pattern work beautifully in event-sourced systems, where the event stream becomes both a log and a coordinator.

State and Events in Harmony

Perhaps ESA’s most intriguing twist is how it handles state. Microservices often silo data into per-service databases, forcing elaborate choreography to keep things consistent. SOA lumped state into big, shared repositories, creating contention. ESA proposes a hybrid: services own their state, but events propagate changes efficiently. Think of a "CustomerUpdated" event carrying just enough payload to keep related services in sync, without the tight coupling of a shared database. It’s a nod to event-driven architecture, tempered by pragmatism.

Does ESA Matter?

I’m cautiously optimistic about ESA. It’s not a silver bullet—none of these architectures are—but it feels like a response to real pain points. Teams tired of Microservices’ sprawl and SOA’s inertia might find it a practical middle ground. In a recent project, I saw a team refactor a microservices mess into four "essential" services, cutting deployment overhead by half and slashing latency from API overuse. The system didn’t just run better; it was easier to reason about.

That said, ESA’s success hinges on discipline. Defining "essential" services requires a deep understanding of your domain—get it wrong, and you’re back to SOA’s bloat or Microservices’ chaos. And while events streamline communication, they bring their own complexity: idempotency, ordering, replay. It’s not a free lunch.

The Pendulum Swings On

From SOA to Microservices to ESA, the arc of service architecture reflects our ongoing quest for balance—between cohesion and independence, simplicity and flexibility. ESA won’t be the final word; the pendulum will swing again as new constraints emerge. But for now, it offers a lens to rethink how we carve up systems, a reminder that good architecture isn’t about chasing trends—it’s about solving problems with clarity and care.

If you’re intrigued, I’d recommend digging into Roshan’s post on the topic https://roshancloudarchitect.me/introducing-essential-service-architecture-esa-for-ui-and-backend-a8faba51eaca. It’s a solid starting point to see ESA in action. As for me, I’ll keep watching, tinkering, and talking with teams to see where this path leads. After all, the joy of architecture lies in the journey, not the destination.