Microservices
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API Gateway Pattern in Microservices
The API Gateway pattern provides a single entry point for client applications to access microservices, acting as a reverse proxy that routes requests to appropriate backend services. Beyond simple routing, API gateways aggregate responses, handle authentication, enforce rate limits, and manage cross-cutting concerns that would otherwise require implementation in every service. This pattern is fundamental to microservices architectures, simplifying client interactions and centralizing infrastructure concerns.
Core Responsibilities
Request Routing maps incoming requests to backend services based on URL paths, HTTP methods, headers, or query parameters. The gateway understands the microservices topology and routes /users to the user service, /orders to the order service, maintaining a single client-facing API despite numerous backend services.
Circuit Breakers: Preventing Cascading Failures
Circuit breakers prevent cascading failures in distributed systems by stopping requests to failing services, allowing them time to recover while providing fast failures to callers. Inspired by electrical circuit breakers that protect circuits from overload, software circuit breakers protect services from being overwhelmed by requests they cannot handle, improving overall system resilience and stability.
The Problem
In distributed systems, services depend on other services. When a downstream service becomes slow or fails, upstream services might wait for responses, exhausting threads or connections. As threads block, the upstream service degrades, affecting its callers. This cascades through the system, potentially bringing down multiple services due to one failure.
Microservices Architecture: Building Distributed Applications
Microservices architecture structures applications as collections of loosely coupled, independently deployable services. Each service implements specific business capabilities, owns its data, and communicates with other services through well-defined APIs. This architectural style enables organizational scalability, technological flexibility, and independent deployment, though it introduces operational complexity.
Core Principles
Service Independence: Each microservice is a separate unit that can be developed, deployed, and scaled independently. Services have their own code repositories, deployment pipelines, and operational tooling.
Service Discovery: Finding Services in Dynamic Environments
Service discovery is the process by which services locate and communicate with each other in dynamic distributed environments. As microservices scale up and down, move between hosts, and fail over, their network locations change constantly. Service discovery automates finding available service instances without hardcoding addresses, enabling the dynamic, elastic infrastructure that characterizes cloud-native applications.
The Problem
In traditional monolithic applications or small-scale distributed systems, service locations are static and can be configured once. A database at db.company.com:5432 remains at that address indefinitely. However, microservices environments are highly dynamic: containers start and stop, autoscaling changes instance counts, deployments replace old instances with new ones, and failures require routing around unhealthy services.
Service Mesh: Managing Microservices Communication
A service mesh is a dedicated infrastructure layer for managing service-to-service communication in microservices architectures. It handles concerns like load balancing, service discovery, failure recovery, metrics collection, and security without requiring application code changes. By moving these capabilities from application libraries into infrastructure, service meshes provide consistent, centralized control over communication patterns across polyglot services.
Architecture
Service meshes use the sidecar proxy pattern, deploying a proxy alongside each service instance. All network traffic flows through these proxies, which implement communication logic. Services believe they’re calling each other directly but are actually calling local proxies that handle the actual network communication.