Microservices Architecture Knowledge Base

Quick reference for microservices architecture patterns and PHP implementation guidelines.

Core Principles

Architecture Overview

┌──────────────────────────────────────────────────────────────────────────┐
│                     MICROSERVICES ARCHITECTURE                           │
├──────────────────────────────────────────────────────────────────────────┤
│                                                                          │
│   ┌──────────┐     ┌──────────────────┐     ┌──────────────────┐        │
│   │  Client   │────▶│   API Gateway    │────▶│   Service A      │        │
│   │          │     │  (Routing/Auth)   │     │  (Own Database)  │        │
│   └──────────┘     └──────────────────┘     └──────────────────┘        │
│                           │                       │                      │
│                           │                       │ async                │
│                    ┌──────▼──────┐          ┌─────▼──────────┐          │
│                    │  Service B  │          │  Message Broker │          │
│                    │ (Own DB)    │◀─────────│  (Events/Cmds)  │          │
│                    └─────────────┘          └────────────────┘          │
│                                                                          │
├──────────────────────────────────────────────────────────────────────────┤
│                                                                          │
│   Decomposition Strategies:                                              │
│   • By Business Capability    - Align with bounded contexts             │
│   • By Subdomain (DDD)        - Core, Supporting, Generic               │
│   • Strangler Fig              - Incremental migration from monolith    │
│                                                                          │
│   Communication:                                                         │
│   • Synchronous  - REST, gRPC, GraphQL (request-response)              │
│   • Asynchronous - Message queues, event streaming                      │
│                                                                          │
└──────────────────────────────────────────────────────────────────────────┘

Service Communication Patterns

Pattern	Type	Use When	Trade-off
REST	Sync	CRUD, simple queries	Easy but coupling
gRPC	Sync	Internal service-to-service, performance-critical	Fast but schema coupling
GraphQL	Sync	Client-driven queries, BFF	Flexible but complex
Message Queue	Async	Reliable delivery, work distribution	Decoupled but eventual consistency
Event Streaming	Async	Real-time, event sourcing, audit trails	Scalable but complex ordering
Request-Reply	Async	Async request needing response	Decoupled but higher latency

API Gateway Patterns

Pattern	Description	When to Use
Simple Proxy	Routes requests to services	Small number of services
Gateway Aggregation	Combines multiple service calls	Reduce client round-trips
BFF (Backend for Frontend)	Gateway per client type	Mobile vs Web vs API clients
Gateway Offloading	Auth, rate limiting, TLS	Cross-cutting concerns

Service Discovery

Approach	How It Works	Example
Client-side	Client queries registry, selects instance	Netflix Eureka
Server-side	Load balancer queries registry	AWS ALB, Kubernetes
DNS-based	DNS SRV records resolve to instances	Consul DNS, CoreDNS
Platform-native	Container orchestrator handles routing	Kubernetes Services

Data Management

Pattern	Description	Consistency
Database per Service	Each service owns its data	Strong (within service)
Shared Database	Services share one database	Strong (anti-pattern!)
Saga	Distributed transaction via events	Eventual
CQRS	Separate read/write models	Eventual
Event Sourcing	Events as source of truth	Eventual
API Composition	Query multiple services, merge results	Eventual

When to Use Microservices vs Monolith

Factor	Monolith	Microservices
Team size	< 10 developers	> 10, multiple teams
Domain complexity	Simple/moderate	Complex, many bounded contexts
Scalability needs	Uniform scaling	Independent scaling per component
Deployment frequency	Infrequent, coordinated	Frequent, independent
Technology diversity	Single stack	Polyglot needed
Organizational maturity	Starting out	DevOps culture, CI/CD mature

Detection Patterns

# Service boundary indicators
Grep: "HttpClient|GuzzleHttp|curl_init" --glob "**/Infrastructure/**/*.php"
Grep: "grpc|protobuf" --glob "**/*.php"

# API Gateway patterns
Grep: "X-Forwarded|X-Request-ID|X-Correlation" --glob "**/*.php"
Glob: **/Gateway/**/*.php

# Service discovery
Grep: "ServiceDiscovery|ServiceRegistry|consul|etcd" --glob "**/*.php"
Grep: "KUBERNETES_SERVICE|SERVICE_HOST" --glob "**/*.env*"

# Database per service
Grep: "DATABASE_URL|DB_CONNECTION" --glob "**/*.env*"
Grep: "DATABASE_HOST|DB_HOST" --glob "**/docker-compose*.yml"

# Inter-service communication
Grep: "AMQPChannel|RabbitMQ|Kafka|SQS" --glob "**/Infrastructure/**/*.php"
Grep: "EventPublisher|MessageBus" --glob "**/*.php"

Advanced Patterns

Strangler Fig Pattern

Incrementally migrate from monolith to microservices:

Phase 1: Proxy all traffic through gateway
Phase 2: Extract one feature to service, route via gateway
Phase 3: Repeat until monolith is empty shell
Phase 4: Decommission monolith

┌─────────┐     ┌──────────┐     ┌──────────────┐
│  Client  │────▶│ Gateway  │────▶│  New Service  │  (extracted)
│          │     │ (Router) │     └──────────────┘
│          │     │          │────▶┌──────────────┐
│          │     │          │     │  Monolith     │  (shrinking)
└─────────┘     └──────────┘     └──────────────┘

Migration Decision:

Factor	Extract First	Keep in Monolith
Change frequency	High	Low
Team ownership	Dedicated team	Shared
Scaling needs	Independent scaling	Uniform
Technology fit	Different stack needed	Same stack fine

API Gateway Aggregation Patterns

Pattern	When	Example
Simple proxy	1:1 route mapping	/users → User Service
Aggregation	Client needs data from N services	Order + Customer + Payment
BFF	Different clients need different data	Mobile vs Web vs API
Offloading	Cross-cutting concerns	Auth, rate limiting, TLS

Database-Per-Service Trade-offs

Aspect	Shared DB	DB per Service
Consistency	ACID transactions	Saga/eventual
Querying	JOIN across domains	API composition
Independence	Coupled deployments	Independent
Complexity	Low	High
Schema changes	Coordinated	Independent

References

For detailed information, load these reference files:

• references/patterns.md — Service mesh, API gateway implementations, service discovery details, data consistency, Strangler Fig, database-per-service
• references/antipatterns.md — Distributed monolith, shared database, missing boundaries, chatty communication