In the exciting world of software development, building with microservices is like assembling LEGO blocks — each piece should have its place and purpose. But how do we decide where one microservice should begin and where another should end? 🤔
Welcome to this joyful journey of right-sizing microservices and discovering how to identify service boundaries the smart way! Whether you're designing from scratch or modernizing a monolith, understanding service boundaries is a superpower that leads to systems that are scalable, maintainable, and flexible.
Let’s explore two proven approaches that can guide you:
✨ Domain-Driven Sizing and
🎉 Event Storming Sizing
…and we’ll wrap things up with a real-world example using a banking application.
✨ Domain-Driven Sizing: Let Business Lead the Way
Domain-Driven Sizing is all about letting your business logic drive your architecture. Instead of splitting services based on technical layers or databases, this approach focuses on business capabilities.
Here’s how it works:
💡 Step 1: Understand the Business
Talk to product owners, business analysts, and users. Find out what they need and how they use the system. Why? Because software should serve the business, not the other way around.
🧠 Step 2: Follow Domain-Driven Design
Use Domain-Driven Design (DDD) to map out your core domains. Each microservice should reflect a specific business function, like Account Management, Loan Processing, or Customer Onboarding.
⌛ Step 3: Be Patient — It Takes Time
This method requires deep understanding and collaboration. But the result? A clean architecture where each service has a clear purpose — no more spaghetti code or tangled logic!
🎉 Event Storming Sizing: Make It a Party! 🎈
Event Storming is a creative and collaborative technique that brings everyone together — developers, domain experts, testers, and even business folks.
It’s like a brainstorming session, but more colorful and focused on events that happen in the system.
🧩 Step 1: Spot the Events
Using sticky notes (or digital tools), identify important events like:
- "Payment Completed"
- "Product Searched"
- "Account Created"
These events tell a story about how your system behaves.
🧭 Step 2: Map Commands and Reactions
Once you know what happens, figure out what causes those events (commands) and what follows (reactions). For example:
- Command: “Apply for Loan”
- Event: “Loan Application Submitted”
- Reaction: “Credit Check Triggered”
🧱 Step 3: Group Events into Services
Now, group related commands, events, and reactions together into logical services. This naturally reveals your service boundaries — and since it reflects real business interactions, your system stays aligned with user needs.
✅ Pro Tip: Event Storming works great during the early planning stage or when redesigning legacy systems.
🏦 Real-World Example: A Bank Application
Let’s put theory into action with a banking example.
Imagine you're building or modernizing a bank’s system using microservices. You need to break down the platform into logical, manageable services.
❌ The Wrong Way: Overcoupling
You might be tempted to group services like this:
- Savings & Trading Account Service
- Cards & Loans Service
Sounds simple, right? But wait — this mixes unrelated domains together! Loans and credit cards operate differently. Grouping them leads to tight coupling, and soon, changing one thing could break everything.
✅ The Right Way: Independent Services
Instead, try this:
Savings Account ServiceTrading Account ServiceDebit Card ServiceCredit Card ServiceHome Loan ServiceVehicle Loan ServicePersonal Loan Service
Now each service focuses on a specific task. They’re independent, easier to maintain, and can scale on their own. This is the true spirit of microservices!
🏁 Wrapping It All Up
Choosing the right size and boundaries for your microservices isn’t just a technical decision — it’s a strategic one.
Whether you use:
- 🧠 Domain-Driven Sizing for deep business alignment
- 🎉 Event Storming for collaborative discovery
…the goal is always the same: create services that are loose, focused, and resilient.
When done right, microservices let you build systems that grow gracefully, adapt quickly, and bring joy to both developers and users. 🌱
💬 Final Words
If you’ve ever struggled with where to draw the line between services — you’re not alone. But with the right mindset and tools, you can master the art of sizing microservices.
So grab some sticky notes, rally your team, and let the boundaries reveal themselves!
Happy coding! 🚀
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