In my work as a Principal Architect helping organizations adopt Event-Driven Architecture (EDA), one question comes up consistently: “When do I create events and how do I govern them?” It’s a fundamental question that gets to the heart of designing effective event-driven systems. From my experience working with teams across different industries, I’ve found that the answer isn’t always straightforward because it depends on understanding the different types of events and their appropriate use cases.

In an Event-Driven Architecture, the system is structured around the production, detection, consumption, and reaction to events. Events are significant changes in state that are identified and processed by various components within the architecture. The classification of events can vary based on the criteria used (e.g., scope, source, or type of data), but generally, events can be categorized into several common types.

Understanding these event classifications is important for making informed decisions about when to create events and how to govern them effectively. Let’s explore the different types of events you may encounter as you adopt EDA.

Event Classifications

1. Domain Events

These are significant to the business domain and represent a change in the domain’s state. For example, in an e-commerce system, a domain event could be “Order Placed” or “Item Shipped”. Domain events are used to trigger workflows and business processes. They are fundamental to Event Sourcing patterns, where the events themselves become the source of truth for aggregate state, and they help maintain consistency within bounded contexts by ensuring all changes are captured and can be replayed.

2. Integration Events

Used to communicate changes across different bounded contexts or services, integration events help maintain consistency across the system’s different parts. For example, when a new user is registered in one service, an integration event can trigger a welcome email from another service. These events are crucial for achieving eventual consistency in distributed systems and often play a key role in saga patterns for managing long-running transactions across multiple services.

3. System Events

These events relate to the operation and health of the system itself, such as service start-up or shut down, error occurrences, or resource utilization spikes. Monitoring systems often use system events to trigger alerts or automated recovery procedures. They are essential for observability platforms, feeding into metrics collection, Service Level Indicators (SLIs), and helping teams maintain Service Level Objectives (SLOs) through real-time system health monitoring.

4. Temporal Events

These are time-based events triggered by reaching specific points in time or intervals. Examples include scheduled tasks (e.g., sending out a daily report) or timeouts (e.g., session expiration). In business contexts, temporal events are crucial for recurring processes like billing cycles, subscription renewals, contract expirations, and compliance reporting deadlines. They help automate time-sensitive business operations and ensure critical processes aren’t missed.

5. Platform Events

Specific to the underlying platform or infrastructure, these events can indicate changes in the environment (e.g., deployment of a new version, scaling operations) or external service statuses (e.g., a third-party API becoming unavailable). In cloud-native environments, platform events include Kubernetes pod lifecycle events, auto-scaling triggers, cloud provider notifications (like AWS CloudWatch alarms), and infrastructure state changes that can trigger automated responses or maintenance workflows.

6. Policy or Rule Events

Triggered when certain rules or policies are applied or breached. For example, a policy event might occur if a transaction exceeds a certain threshold, necessitating additional checks. These events are particularly important in regulated industries for compliance monitoring, fraud detection, and governance workflows. They can trigger automated responses like additional verification steps, audit logs, or escalation procedures to ensure business rules and regulatory requirements are consistently enforced. In data privacy contexts, policy events can trigger GDPR compliance workflows such as data deletion requests, consent management, or PII access logging to maintain regulatory compliance and protect user privacy.

7. User or Action Events

Initiated by user actions or interactions, such as clicks, form submissions, or navigation events. These are often used in analytics, user interface interactions, and to drive user-specific processes. They enable behavioral analytics, user journey tracking, and personalization engines. In modern applications, these events feed into real-time recommendation systems, A/B testing frameworks, and customer experience optimization platforms. Common consumers of user events include analytics platforms like Google Analytics, Adobe Analytics, and custom event tracking systems that help organizations understand user behavior and optimize their digital experiences.

8. Data Events

Involve changes to data, such as creation, modification, or deletion of records. Data events are crucial in systems where data consistency and integrity across services or databases are paramount. Change Data Capture (CDC) is a common pattern used to generate data events automatically when database records are modified, enabling real-time data synchronization across distributed systems.

Event Type

Implementation Considerations

Event Type Selection

It’s important to note that not all organizations will have a need for all of these event types. The selection of event types depends on several factors:

  • Business Requirements: The specific needs of your domain and business processes
  • System Complexity: Simpler systems may only require domain and integration events
  • Organizational Maturity: Teams new to EDA might start with a subset and gradually adopt more types
  • Infrastructure Capabilities: Available tooling and platform support may influence choices

Getting Started

Organizations typically begin their EDA journey by implementing:

  1. Domain Events - Core to business logic and workflows
  2. Integration Events - Essential for service communication
  3. System Events - Critical for monitoring and operations

Additional event types like temporal, platform, and policy events can be introduced as the system matures and requirements evolve.

Avoiding Event Creep

One of the most common pitfalls I’ve observed is what I call “event creep”—the gradual proliferation of events without proper governance. Without clear guidelines on when to create events and how to classify them, teams tend to create events for every conceivable state change, leading to an overwhelming number of events that become difficult to manage, understand, and maintain. This typically results in inconsistent naming conventions, overlapping event responsibilities, and a system that’s harder to reason about than the monolith it replaced. Establishing clear event governance early—including naming standards, approval processes, and regular event audits—is crucial for preventing this anti-pattern.

Best Practices & Key Takeaways

Strategic Approach:

  • Start with the essentials: Domain events for business logic, integration events for service communication, and system events for monitoring
  • Not all event types are needed: Choose event types based on your business requirements, system complexity, and organizational maturity
  • Evolve gradually: Additional event types like temporal, platform, and policy events can be introduced as your system and team mature

Governance & Management:

  • Avoid event creep: Establish clear governance early with naming standards, approval processes, and regular event audits
  • Governance is crucial: Proper event classification and governance prevent the system from becoming harder to manage than the monolith it replaced

Technical Implementation:

  • Ensure proper event naming conventions and schemas
  • Implement appropriate event storage and replay mechanisms
  • Consider event ordering and consistency requirements
  • Plan for event versioning and backward compatibility

Conclusion

So, back to that original question: “When do I create events and how do I govern them?” The answer lies in understanding your specific context and requirements. Each type of event plays a vital role in an Event-Driven Architecture, facilitating communication between different parts of the system, enabling decoupling, and enhancing the system’s responsiveness and flexibility.

Start by identifying which event types align with your business needs and technical requirements. Remember, you don’t need to implement all event types from day one. Begin with the essentials—domain events for your core business logic, integration events for service communication, and system events for operational awareness.

As your system matures and your team becomes more comfortable with event-driven patterns, you can gradually introduce additional event types like temporal, platform, and policy events. The key is to maintain clear governance around event schemas, naming conventions, and lifecycle management.

By understanding and leveraging these event classifications thoughtfully, you’ll be well-equipped to design more robust, scalable, and maintainable event-driven systems that truly serve your organization’s needs.