You’re a professional software engineer really good at message broker system like
kafka.
Answer my questions about the message broker system as you are the engineer I mentioned above, with a spatial examples.
As a professional software engineer experienced with message broker systems like Kafka, I can provide guidance on designing events and best practices to follow, along with potential pitfalls to avoid. Let's delve into your questions:
What is the best practice for designing events using a message broker?
- Define Clear Event Contracts: It's crucial to establish a clear contract for each event, specifying the event name, payload structure, and any associated metadata. Use a standardized format like JSON or Avro to ensure compatibility and ease of understanding across different services.
- Use Domain-Driven Design (DDD) Principles: Apply DDD concepts to your event design, focusing on the ubiquitous language and domain-driven modeling. Events should reflect meaningful domain actions or state changes, ensuring they represent business-relevant occurrences.
- Be Granular and Atomic: Design events to capture granular changes or actions within your system. Events should be atomic and self-contained, carrying all the necessary information for event consumers to understand and react to them without relying on additional external resources.
- Avoid Tight Coupling: Ensure events remain loosely coupled to enable independent evolution of services. Avoid including unnecessary details about specific consumers or relying on tight dependencies between producers and consumers.
- Version Events: Plan for event evolution by including versioning in your event schema. This allows for backward compatibility and smooth migration when modifying event structures.
- Consider Event Sourcing: For complex domain scenarios, event sourcing can provide significant benefits. It involves storing all changes to an application's state as a sequence of events, providing a comprehensive audit log and enabling state reconstruction at any point in time.
What should I avoid when designing events for a message broker?
- Large Payloads: Avoid sending large event payloads as it can impact network bandwidth, serialization/deserialization performance, and overall system efficiency. Instead, strive for smaller, focused payloads that capture only the necessary data.
- Overusing Chatty Events: Be mindful of overusing events for every small internal system action. Excessive event generation can lead to unnecessary network traffic and increased complexity. Focus on events that provide value to downstream consumers or represent significant business events.
- Mixing Commands and Events: Differentiate between commands and events. Commands represent requests for action, while events convey notifications of completed actions or state changes. Mixing the two can lead to confusion and improper handling by consumers.
- Not Considering Event Replay: When designing events, think about how consumers handle event replay scenarios. Ensure that consuming services can handle duplicate events and process them idempotently without causing unintended side effects.
- Lack of Error Handling: Events should include error handling mechanisms such as error codes, error messages, or metadata indicating failure scenarios. This helps consumers identify and handle errors gracefully.
- Inadequate Event Documentation: Properly document your events, including their purpose, structure, and any conventions or guidelines for their usage. Clear documentation enables better understanding and collaboration among teams working with the events.
Remember, these are general best practices, and the specific design considerations may vary based on your system's requirements and the domain you are working in.
- What is the difference of commands and events?
Certainly! Let's dive into your questions:
What is the difference between commands and events?
- Commands: Commands represent requests or directives for an action to be performed. They are typically initiated by a client or an external entity and sent to a specific service or component responsible for executing the requested action. Commands are imperative in nature and often contain instructions or parameters needed to perform the desired operation. For example, a "CreateUserCommand" may contain user details such as name, email, and password, instructing the system to create a new user.
- Events: Events, on the other hand, represent something that has happened or a state change that has occurred within the system. They are notifications or facts about something that has taken place, and they do not convey any instruction or command to perform an action. Events are typically generated by services or components within the system to communicate important occurrences to other interested components. For example, a "UserCreatedEvent" may be emitted after a new user is successfully created, indicating that the user creation process has occurred.
Commands and events serve different purposes and have distinct characteristics. Commands drive the system's behavior by requesting specific actions, while events inform other parts of the system about past actions or state changes.
Event Sourcing:
Event sourcing is an architectural pattern where the state of an application is derived by storing a sequence of events that have occurred. Instead of persisting only the current state, event sourcing captures the series of events that led to the current state. This approach offers several benefits:
- Comprehensive Audit Trail: By storing events, event sourcing provides a complete history of how the application's state evolved over time. This audit trail can be valuable for debugging, compliance, or regulatory purposes.
- Replayability and Temporal Queries: With event sourcing, it is possible to reconstruct the state of the application at any point in time by replaying the events. This allows for temporal queries, analysis, or rebuilding the application's state in case of issues or data corruption.
- Business Insights and Versioning: Events carry business-relevant information, making it easier to gain insights into user behaviors, trends, or patterns. Additionally, versioning events enables handling changes in business requirements or system upgrades by providing compatibility and allowing for smooth migration.
Spatial Examples of Event Versioning:
Event versioning is essential to handle changes in event structures over time while maintaining compatibility with existing consumers. Here are some spatial examples:
{
"eventName": "UserCreated",
"version": 1,
"payload": {
"userId": "123",
"name": "John Doe",
"email": "[email protected]"
}
}
{
"eventName": "UserCreated",
"version": 2,
"payload": {
"userId": "123",
"name": "John Doe",
"email": "[email protected]",
"age": 30
}
}
JSONversion field and consider the compatibilityTypeScriptinterface HotDeal {
id: number;
title: string;
link: string;
}
interface PpomppuHotDeal extends HotDeal {}
interface FmKoreaPopularHotDeal extends HotDeal {}
interface FmKoreaGeneralHotDeal extends HotDeal {
seller: string;
productPrice: string;
shippingCharge: string;
category: string;
}
// candidate 0
interface HotDealUpdated_MK1 {
version: number;
timestamp: Date;
listOfHotDeal: (
| PpomppuHotDeal
| FmKoreaPopularHotDeal
| FmKoreaGeneralHotDeal
)[];
}
// candidate_1
interface HotDealUpdated_MK2 {
version: number;
sourceAndType: string;
timestamp: Date;
listOfHotDeal:
| PpomppuHotDeal[]
| FmKoreaPopularHotDeal[]
| FmKoreaGeneralHotDeal[];
}