Why do we need eventdriven architectures in microservices

作者：禅与计算机程序设计艺术

1.简介

Event-driven architecture is one of the critical architectural patterns that has become increasingly popular among software developers and architects over the past few years. In this article, I will provide a brief overview of what an event-driven architecture is, why it matters, and how to use it effectively in microservices.
The article starts with a background introduction explaining the importance of building reliable and scalable systems using microservices. We then go on to explain the basic concepts and terminology involved in event-driven architectures such as events, event sources, event handlers, message brokers, etc. Next, we discuss the core algorithmic principles behind event processing along with specific operations and mathematical formulas used for event handling. Finally, we present concrete code examples and explanations to illustrate how event-driven architectures work in practice.
This article aims to be informative, concise, and easy to understand by providing practical insights into event-driven architecture design and implementation within a microservice environment. By reading this article, you should gain a deeper understanding of microservices, their role in enterprise-level applications, and the importance of implementing event-driven architectures within them.
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Article Structure
Introduction: About Microservices and Background on Event-Driven Architecture

1. What are microservices?

• Definition
• Advantages & Disadvantages

2. Architectural Patterns and Anti-patterns

• Microservices Architecture Style
• Service Discovery and Load Balancing
• API Gateway
• Choreography vs Orchestration

3. Why Do We Need Event-Driven Architectures in Microservices?

• Architecture Paradigm Shift
• Flexible Scalability
• Better Performance

4. Basic Concepts and Terminology
5. Core Algorithm and Operations
6. Practical Examples and Explanations
7. Conclusion: Summary and Future Directions
   References
   Appendix A: FAQ

1.Introduction

1.1.About Microservices

1.1.1 Definition

Microservices refers to a software development approach where an application is composed of small, independent services, each running its own process and communicating through well-defined APIs. Each service can be developed, tested, and deployed independently, which allows for faster development cycles and increased flexibility when making changes. Additionally, microservices can scale horizontally to accommodate varying traffic levels without downtime or failures. Microservices can be hosted on different infrastructure platforms depending on needs, making them more portable and flexible than monolithic applications. Microservices can also leverage cloud computing resources for cost savings and better performance compared to traditional monolithic applications.

1.1.2 Advantages & Disadvantages

Here are some advantages of using microservices:

1. Independent deployment – Microservices allow teams to develop, test, and deploy individual components of an application, leading to faster turnaround times and less risk of errors. This reduces overall costs and increases security.
2. Smaller codebase – Within a microservices architecture, each component is typically much smaller and easier to maintain, resulting in a smaller codebase and reduced complexity. This improves developer productivity and speeds up deployment.
3. Easier scaling – Microservices can easily scale out horizontally simply by adding additional instances, making it easier to handle large volumes of requests. It’s also possible to scale down if needed, reducing overhead and improving system stability.
4. Cloud native – Microservices make it easier to transition your application to the cloud because they are designed to run independently and scale horizontally, allowing for greater elasticity and resiliency.
5. Code ownership – Microservices enable code ownership to be shared across multiple teams, further enhancing collaboration between business units and improved quality control.
   However, there are also some potential disadvantages of using microservices:
6. Complexity – Building and maintaining microservices requires careful planning, design, and implementation. Managing dependencies and interdependencies between services adds additional complexity.
7. Distributed nature – Although microservices offer many benefits, distributed systems introduce new challenges such as complex communication protocols, data consistency, and coordination.
8. Debugging – Because each microservice runs independently, debugging can become challenging since issues may not always manifest themselves in the same place.
   Overall, microservices are emerging as a powerful architectural pattern that offers numerous benefits but also presents significant challenges. Depending on your context, it may still be beneficial to build a single monolithic application instead.

1.2.Background on Event-Driven Architecture

In recent years, microservices have gained prominence due to their ability to address both the scalability and modularity requirements of modern web applications. While microservices provide several advantages, such as independent deployment and modularization, they also come with their own set of problems such as decentralized decision-making, tight coupling, and statelessness. One solution to these problems is to adopt a more event-driven architecture paradigm.
An event-driven architecture breaks down the application logic into discrete, loosely coupled modules called “event listeners”. These listeners receive events (e.g., user registration, order placement) and react accordingly, possibly causing other events to occur in response. For example, when a user registers, their information is sent to an “account creation” listener that creates a new account record. When the user places an order, payment details are passed to a “payment processor” listener that triggers the necessary processes such as credit card authorization.
An event-driven architecture differs from traditional request-response architectures in two main ways:

1. Loose coupling – Events trigger actions rather than direct responses, meaning that the triggering action does not depend directly on the result of another action. This simplifies error handling, makes it easier to debug, and enables better scalability.
2. Asynchronous communication – Since events are emitted asynchronously and may take time to reach all interested parties, asynchronous communication is often preferred over synchronous messaging patterns.
   In summary, event-driven architectures combine the scalability of microservices with the flexibility and robustness of centralized architectures while addressing common challenges such as decoupling and reliability. They are becoming increasingly popular in modern software engineering and delivering significant value to organizations looking to implement microservices.

2.Basic Concepts and Terminology

2.1.Events and Event Sources

An event occurs whenever something happens that you want to track and respond to in real-time. Some examples include user login, device motion detection, button click, purchase completion, and employee promotion.
To capture these events, you would create event sources that emit or produce these events. There are various types of event sources, including hardware devices, mobile apps, websites, and databases. Event sources can be divided into three categories based on their level of fidelity:

1. Low Fidelity – Capture only high-level events such as user activity or device status.
2. Medium Fidelity – Capture detailed events related to user behavior, such as clicks or purchases.
3. High Fidelity – Capture every aspect of an interaction, including timing, location, and content.
   Once an event source emits an event, it passes it on to an event broker. The event broker stores and manages the event until it is ready to be processed.

2.2.Event Handlers

An event handler is a piece of software that listens for events and responds to them. When an event arrives at an event handler, it performs certain actions based on the type of event received. Some examples of event handlers could be sending an email notification, updating a database record, logging an alert, or calling an external API.

2.3.Message Brokers

A message broker receives messages from event sources and distributes them to subscribers who register interest in particular topics. Message brokers help ensure that messages are delivered exactly once, ensuring that events are handled correctly even in case of network failure or subscriber failure.

2.4.Topics and Subscriptions

Topics define the category or subject of an event. Each topic can have zero or more subscriptions that specify the interested parties for that topic. Subscribers can subscribe to multiple topics.

2.5.Event Store

An event store is a repository of stored events that supports querying, aggregating, and analyzing historical events. An event store provides a timeline view of events over time, enabling you to identify trends, patterns, and relationships between events. You can use various storage mechanisms to implement an event store, such as relational databases, NoSQL databases, file systems, object storage, or distributed blockchains.
The primary purpose of an event store is to support event sourcing, an architectural pattern that enables capturing and replaying of domain events in a consistent and accurate manner. Event sourcing involves storing the full sequence of events that describe the state of an entity over time so that it can be reproduced at any point in time to recover the current state of the entity. Using an event store can greatly simplify the development of complex systems that rely on eventual consistency and ensure that updates are applied consistently throughout the system.

3.Core Algorithm and Operations

3.1.Pub/Sub Messaging Protocol

Pub/sub messaging protocol is a method of asynchronous messaging commonly used in microservices architecture. The idea behind pub/sub is simple – publishers send messages to a topic, which are then routed to any subscribed clients. Clients can either consume the message immediately or later, depending on their subscription settings.
The most important concept behind pub/sub messaging is topic. Topic is a category or channel to which messages can be published. Subscribers can subscribe to one or more topics to get notifications of new messages.
In pub/sub model, there are no queues like in queue-based messaging systems. Instead, subscribers pull messages from the publisher’s server or stream endpoint in real-time. This means that the delivery of messages takes place instantaneously, regardless of the number of consumers currently available.
Below are the steps performed by a publisher in a pub/sub system:

1. Connect to the broker server.
2. Identify the topic to which the message needs to be published.
3. Encode the message into binary format (JSON, XML).
4. Send the encoded message to the corresponding topic exchange.
   Subscribers perform the following tasks to receive messages:
5. Connect to the broker server.
6. Create a durable or non-durable subscription on the desired topic.
7. Start consuming messages by subscribing to the desired topic(s).
8. Receive messages pushed by the publisher and acknowledge receipt.
9. Process the message according to the application logic.
   Publisher-Subscriber Model
10. Publishers generate events that are placed onto a message queue or message bus.
11. Subscribers poll or listen to the event queue or message bus, waiting for new events to appear.
12. When a new event appears, the subscriber reads and processes it.
    In the above diagram, users submit feedback via forms or ratings, which are detected by the event-listener microservices. The feedback events are then sent to the message broker for consumption by interested downstream microservices.

3.2.Implementing Pub/Sub in a Microservices Environment

Implementing pub/sub messaging protocol in a microservices environment requires us to consider the following points:

1. Decide upon the technology stack to be used for implementing the pub/sub system. RabbitMQ, Kafka, and Apache Pulsar are some popular options.
2. Choose appropriate messaging models for different scenarios. RPC style messaging might not be suitable for event driven architecture, whereas the event based model fits best here.
3. Choose a communication mechanism to communicate between microservices. RESTful API or Message Queueing might be suitable here.
4. Ensure proper configuration of the broker servers to optimize throughput and reduce latency.
5. Monitor the health of the messaging system and identify bottlenecks.
6. Test and tune the system to achieve optimal results.
   In conclusion, implementing an effective pub/sub messaging protocol in a microservices environment requires careful planning and attention to detail. Following are some key points to keep in mind when implementing pub/sub messaging in microservices:
7. Use public and private topics to separate internal and external concerns. Internal topics should only be consumed by relevant microservices, while external topics should not contain sensitive or proprietary information.
8. Provide clear documentation for the usage of each topic, including recommended formats and structure of the messages.
9. Use SSL certificates and encryption techniques to protect the messages during transit.
10. Enable authentication and authorization mechanisms to restrict access to specific topics.

3.3.Implementation Example

Let’s take an example scenario where we need to implement an e-commerce platform where customers can review products, add reviews, update their existing reviews, delete their reviews.
Here are the steps to implement this functionality using event-driven architecture:

1. Decide upon the technologies to be used for implementing the event-driven architecture. We’ll choose RabbitMQ as our message broker and Java programming language for implementing the event-driven microservices.
2. Define the events that will be triggered when a customer interacts with the product catalogue, such as clicking on a product, submitting a rating, editing a review, deleting a review.
3. Implement event publishing microservices. These microservices will read data from the respective data sources and publish the events to the message broker.

4. Implement event listening microservices. These microservices will receive the events from the message broker and execute the required business logic, such as updating the product inventory, calculating product ratings, and indexing search data.

// Configuring rabbitmq for event-driven architecture
bindings:
- exchange:
 name: ecomm.events
 type: topic
destination:
 name: 'ecomm.*'
 type: topic
  
// Bindings represent rules for routing incoming events
   

6. Verify the correct functioning of the event-driven architecture by simulating interactions with the platform. For instance, simulate customer reviews being added, updated, and deleted to verify that the correct events are being generated and executed by the appropriate microservices.
7. Optimize the system by tuning the configurations of the message broker, microservices, and message sizes to achieve maximum throughput.

3.4.Conclusion

In this article, we discussed what microservices are, why we need event-driven architecture, and provided an example implementation using RabbitMQ and Java programming language. We also explored the core concepts of pub/sub messaging and explained how it works in the context of microservices architecture. By doing this, we hope to give readers a better understanding of microservices and how event-driven architecture can benefit them in achieving higher agility and responsiveness.文章来源地址https://uudwc.com/A/Gdpn3