To address building scalable cloud applications, here are different perspectives on cloud architecture patterns, focusing on event-driven architecture and microservices.

Event-Driven Architecture (EDA)

This paradigm focuses on systems that communicate through asynchronous "events," or changes in state. It is a powerful approach for developing reactive, decoupled, and scalable applications

Microservices Architecture

Microservices are an architectural style that structures an application as a collection of small, autonomous, and independently deployable services. This approach provides modularity, extensive parallelism, and cost-effective scaling. 

Patterns within microservices

• Strangler Fig Pattern: Used for migrating a monolithic application to a microservices architecture. This involves gradually replacing specific functionalities of the monolith with new microservices. Over time, the new services "strangle" the old application until the monolith can be retired.
• API Gateway: Serves as a single entry point for all client requests, routing them to the appropriate microservice. This simplifies the client-side experience and centralizes cross-cutting concerns like security, monitoring, and load balancing.
• Bulkhead Pattern: Isolates system components to prevent a single point of failure from cascading and taking down the entire system. This is analogous to a ship's bulkheads, which contain a breach to a single compartment.
• Sidecar Pattern: Deploys a companion container alongside a main application container. The sidecar handles shared functionality such as logging, monitoring, and security, abstracting it from the application logic. This pattern is often used in a service mesh with Kubernetes.
• Retry and Circuit Breaker: These are resilience patterns. The Retry pattern automatically re-attempts failed operations in case of transient failures, often with an exponential backoff. The Circuit Breaker pattern prevents a service from continuously calling a failing one, allowing the failing service to recover and avoiding cascading failures.
• Decomposition Patterns:
  • Decomposition by Business Capability: The most common approach, where services are structured around business domains (e.g., payment, shipping, and inventory).
  • Decomposition by Subdomain: Used for complex domains, splitting a service into smaller subdomains based on domain-driven design principles.
• Orchestration vs. Choreography: These patterns describe how microservices coordinate to complete a task.
• Orchestration: A central orchestrator service calls and controls the sequence of steps and microservices involved in a business process. This provides explicit control but can create a potential bottleneck.
• Choreography: Microservices operate autonomously and react to events without a central coordinator. This is a highly decentralized and loosely couped approach but can be more difficult to debug. 

Hybrid architectures

In practice, most real-world cloud-native applications combine these approaches.

• Event-driven communication is a natural fit for microservices, allowing them to remain decoupled and highly resilient.
• The API Gateway pattern can handle synchronous, request-based calls from clients, while internal service-to-service communication is driven by an event bus, leveraging the benefits of both synchronous and asynchronous communication.
• The choice between specific patterns often depends on the project's requirements for consistency, performance, and complexity.