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SaaS Architecture & Startup Engineering · Lesson

Event Storming for Microservices

Utilize Event Storming as a collaborative technique to discover domain events and model complex business processes for your SaaS.

Event Storming for Microservices is a free SaaS Architecture & Startup Engineering lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the SaaS Architecture & Startup Engineering learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

What is Event Storming?

Event Storming is a fun, collaborative workshop technique to understand complex business domains. It helps teams visualize how things happen in a system.

Imagine a room full of sticky notes! Teams map out a business process by focusing on the "events" that occur, making it easier to see the big picture.

Why Event Storm for Microservices?

For SaaS, especially with microservices, understanding domain boundaries is key. Event Storming helps:

  • Break down monoliths: Clearly identifies areas to split.
  • Define service boundaries: Groups related events and actions into potential services.
  • Improve communication: Gets everyone on the same page, from business to tech.

The Event Storming Canvas

Event Storming uses different colored sticky notes to represent various elements of your domain:

  • Orange: Domain Events (what happened?)
  • Blue: Commands (what triggers an event?)
  • Yellow: Aggregates (who performs a command?)
  • Green: Read Models (how users view data?)
  • Purple: Policies (rules reacting to events)

Step 1: Discovering Domain Events

This is the starting point! Think about "what happened?" in your business process. Events are facts from the past, always written in past tense.

Examples:

  • OrderPlaced
  • PaymentReceived
  • UserRegistered
  • SubscriptionCancelled

These are the core truths of your system.

Coding a Simple Event

While Event Storming is visual, the events we discover often translate into code. Here's how a simple OrderPlaced event might look in a Java application:

Try running this example to see how an event could be represented and "published" (here, just printed).

public class OrderPlacedEvent {
  private String orderId;
  private double amount;
  private String customerId;

  public OrderPlacedEvent(String orderId, double amount, String customerId) {
    this.orderId = orderId;
    this.amount = amount;
    this.customerId = customerId;
  }

  public String toString() {
    return "OrderPlacedEvent {id='" + orderId + "', amount=" + amount + ", customerId='" + customerId + "'}";
  }

  public static void main(String[] args) {
    OrderPlacedEvent event = new OrderPlacedEvent("ORD123", 99.99, "CUST456");
    System.out.println("New event generated: " + event.toString());
  }
}

Step 2: Identifying Commands

After events, we look for commands. A command is an explicit request to do something, which usually leads to an event (or multiple events).

Ask: "What action caused this event to happen?" Commands are usually imperative verbs.

  • PlaceOrder (leads to OrderPlaced)
  • ProcessPayment (leads to PaymentReceived)
  • RegisterUser (leads to UserRegistered)

Step 3: Pinpointing Aggregates

Aggregates are the "who" or "what" that receives a command and produces an event. They are transactional consistency boundaries – meaning everything within an aggregate changes together.

Think of them as the "model" or "entity" in your code that holds state and enforces business rules.

  • Order aggregate handles PlaceOrder.
  • PaymentProcessor handles ProcessPayment.

Step 4: Read Models & Policies

Read Models (Green): These are how users or other systems query information. They are optimized for reading, often denormalized views built from events.

Policies (Purple): These are business rules that react to events. For example, "when an OrderPlaced event occurs, then send a confirmation email."

From Storm to Bounded Contexts

As you map out your domain, you'll see natural clusters of events, commands, and aggregates. These clusters often define your Bounded Contexts.

A Bounded Context is a logical boundary within which a specific domain model is defined and applicable. This is crucial for designing independent microservices!

Benefits Beyond Design

Event Storming doesn't just help with technical design; it fosters a shared understanding across the entire team.

  • Shared Language: Everyone uses the same terms.
  • Knowledge Transfer: New team members quickly grasp complex flows.
  • Problem Identification: Uncovers hidden assumptions and issues early.

Quick Check

Event Storming uses different colored sticky notes to represent various domain elements. Match the sticky note color to its correct description.

Recap: Event Storming Toolkit

You've learned that Event Storming is a powerful, visual technique to understand complex domains. By focusing on Domain Events, you can identify Commands, Aggregates, Read Models, and Policies.

This collaborative approach helps in defining clear Bounded Contexts, making it an invaluable tool for designing robust and scalable microservices in your SaaS architecture.

Frequently asked questions

Is the “Event Storming for Microservices” lesson free?

Yes — the full text of “Event Storming for Microservices” is free to read here on the web, and the SaaS Architecture & Startup Engineering course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the SaaS Architecture & Startup Engineering course, upgrade to CoddyKit PRO.

What will I learn in “Event Storming for Microservices”?

Utilize Event Storming as a collaborative technique to discover domain events and model complex business processes for your SaaS. You practise SaaS Architecture & Startup Engineering with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start SaaS Architecture & Startup Engineering?

No prior experience is required. SaaS Architecture & Startup Engineering on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Event Storming for Microservices” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this SaaS Architecture & Startup Engineering lesson?

Yes. Every SaaS Architecture & Startup Engineering lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Bounded Contexts & Aggregates
  2. Event Storming for Microservices
  3. Strategic Design & Context Mapping
  4. Ubiquitous Language and the Domain Model
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