goplt/docs/content/requirements.md

Requirements

HIGH‑LEVEL ARCHITECTURAL PRINCIPLES

Principle	Why it matters for a modular platform	How to enforce it
Separation of Concerns (SoC)	Keeps core services (auth, audit, config) independent from business modules.	Use layered or hexagonal/clean‑architecture boundaries.
Domain‑Driven Design (DDD) Bounded Contexts	Allows each module to own its own model & rules while sharing a common identity kernel.	Define a Core Context (Identity, Security, Infrastructure) and Feature Contexts (Billing, CMS, Chat, …).
microMicroservices Architecture	Each service is independently deployable from day one. Services communicate via gRPC/HTTP through service clients.	Each service has its own entry point (cmd/{service}/), database connection, and deployment configuration.
Plug‑in / Extension‑point model	Enables customers or internal teams to drop new features without touching core code.	Export well‑defined interfaces (e.g., IUserProvider, IPermissionResolver, IModuleInitializer).
API‑First	Guarantees that any UI (web, mobile, CLI) can be built on top of the same contract.	Publish OpenAPI/GraphQL schema as part of the build artefact.
Security‑by‑Design	The platform will hold user credentials, roles and possibly PII.	Centralize authentication, authorization, audit, rate‑limiting, CORS, CSP, secure defaults.
Observability	You need to know when a plug‑in crashes or misbehaves.	Provide structured logging, metrics, tracing, health‑checks, central error bus.
CI/CD‑Ready Boilerplate	Keeps the framework maintainable and encourages best‑practice adoption.	Include GitHub Actions / GitLab CI pipelines that run lint, unit, integration, contract tests, and a publish step.
Configuration‑as‑Code	Each module may need its own settings but you want a single source of truth.	Use a hierarchical config system (environment > file > secret store).
Multitenancy (optional)	If you plan SaaS, the core must be ready to isolate data per tenant.	Provide tenant‑aware repository abstractions and tenant‑scoped middlewares.
Versioning & Compatibility	Modules evolve; the core should never break existing plug‑ins.	Adopt semantic versioning + backwards‑compatibility shim layer (e.g., deprecation warnings).

---

LAYERED / HEXAGONAL BLUEPRINT

+---------------------------------------------------+
|                     Presentation                  |
| (REST/GraphQL/ gRPC Controllers, UI SDKs, CLI)    |
+-------------------+-------------------------------+
|        Application Services (Use‑cases)          |
|  - orchestrate core & feature modules            |
|  - enforce policies (RBAC, rate‑limit)           |
+-------------------+-------------------------------+
|            Domain (Business Logic)               |
|  - Core Entities (User, Role, Permission)       |
|  - Domain Services (PasswordPolicy, TokenMgr)   |
+-------------------+-------------------------------+
|           Infrastructure / Adapters              |
|  - Persistence (ORM/NoSQL Repositories)         |
|  - External services (Email, SMS, OIDC)         |
|  - Event bus (Kafka/Rabbit, In‑process)         |
|  - File storage, Cache, Search                  |
+---------------------------------------------------+
|                Platform Core (Kernel)            |
|  - DI container, Module loader, Config manager   |
|  - Cross‑cutting concerns (Logging, Metrics)    |
|  - Security subsystem (AuthN/AuthZ, Token Issuer)|
+---------------------------------------------------+

All layers talk to each other through interfaces defined in the Core kernel. Feature modules implement those interfaces and register themselves at startup.

---

CORE KERNEL (INFRASTRUCTURE ONLY)

The core kernel provides foundational infrastructure services that all other services depend on. It contains no business logic and is purely infrastructure.

CORE SERVICES (INDEPENDENT MICROSERVICES)

Core services provide business logic and are deployed as separate, independently scalable services. Each service has its own database connection, API endpoints, and deployment configuration.

INFRASTRUCTURE ADAPTERS (SHARED SERVICES)

These adapters provide infrastructure capabilities that services can use.

Module	Core responsibilities	Public API / Extension points
Identity‑Management	- User CRUD (local + federation) - Password hashing, reset flow - Email/Phone verification	IUserRepository, IUserService, IExternalIdpProvider
Roles & Permissions	- Role hierarchy (role → permission set) - Permission definitions (string, enum, policy) - Dynamic permission evaluation (ABAC)	IPermissionResolver, IRoleService
Authentication	- JWT / OAuth2 Access & Refresh tokens - OpenID Connect Provider (optional) - Session Management (stateless + optional stateful)	IAuthService, ITokenProvider
Authorization Middleware	- Enforce RBAC/ABAC on each request - Policy DSL (e.g., hasPermission('project.read') && resource.ownerId == user.id)	IAuthorizationHandler
Audit & Activity Log	- Immutable log of security‑relevant actions - Correlation IDs, actor, target, timestamp	IAuditSink, IAuditService
Configuration	- Hierarchical sources (env, files, secret manager) - Validation schema (JSON‑Schema / Yup / JSR‑380)	IConfigProvider
Health & Metrics	- /healthz, /ready, /metrics endpoints - Export to Prometheus, Grafana, CloudWatch	IHealthCheck, IMetricsRegistry
Error Handling	- Centralized error objects, stack trace masking - Automatic mapping to HTTP status - Exception‑to‑event publishing	IErrorMapper, IErrorBus
Logging	- Structured JSON logs (level, requestId, userId) - pluggable sinks (stdout, file, ELK, Cloud Logging)	ILoggerFactory
Notification	- Email, SMS, Push (FCM/APNs), Webhooks - Queue‑backed delivery, retries	INotificationService
File / Blob Storage	- Abstracted bucket API (upload, version, signed URLs)	IBlobStore
Scheduler / Background Jobs	- Cron‑like tasks, queue workers, retry/back‑off policies	IJobScheduler, IJobProcessor
Internationalization (i18n)	- Message catalog, locale negotiation, runtime translation	I18nService
API Gateway (optional)	- Rate‑limit, request/response transformation, API‑key handling, request routing to modules	IGatewayPlugin
Multitenancy (optional)	- Tenant identification (sub‑domain, header, JWT claim) - Tenant‑scoped data isolation primitives	ITenantResolver, ITenantContext

Tip: Pack each module as a separate NPM/ Maven / NuGet / Go module with its own package.json / pom.xml etc. The platform’s bootstrapper loads every module that implements IModuleInitializer (or similar) and calls ConfigureServices / RegisterRoutes.

---

EXTENSION‑POINT DESIGN (HOW PLUG‑INS HOOK IN)

1. Module Manifest – a tiny JSON/YAML file (module.yaml) that declares:

   • Module name, version, dependencies (core ≥ 1.2.0, other modules)
   • Public routes (e.g., /api/v1/blog/**)
   • Required permissions (auto‑generated from source annotations)
   • UI assets (static folder, React component entry point)

2. Bootstrap Interface

   export interface IModuleInitializer {
       /**
        * Called during platform start‑up.
        * Register services, routes, policies, background jobs.
        */
       init(app: IApplicationBuilder, container: IServiceContainer): Promise<void>;
   }
   

3. Dependency Injection (DI) Conventions

   • Core registers contracts (IUserRepository, IPermissionResolver) as singletons.
   • Modules register implementations with a named scope (e.g., UserRepository:Local).
   • Override is possible via module ordering or explicit container.override(...).

4. Policy/Permission Extension

   // core lib
   export type Permission = `${string}.${string}`; // e.g., "blog.post.create"
   
   // module
   export const BLOG_PERMS = {
       POST_CREATE: 'blog.post.create',
       POST_READ:   'blog.post.read',
       POST_UPDATE: 'blog.post.update',
       POST_DELETE: 'blog.post.delete',
   } as const;
   

5. Event Bus & Hooks

   • Central topic: platform.* (user.created, role.assigned, tenant.created)
   • Modules can publish and subscribe via IEventBus.
   • Provide synchronous guard hooks (beforeUserCreate, afterRoleDelete) for validation & side‑effects.

6. UI Plug‑in System

   • Serve a manifest at /modules that front‑end bundles read to render navigation.
   • Encourage Web Component / Module Federation pattern for SPA integration.

---

SAMPLE REPOSITORY LAYOUT (language‑agnostic)

/platform-root
│
├─ /cmd                                    # ---- Service Entry Points ----
│   ├─ /api-gateway                        # API Gateway service
│   │   └─ main.go
│   ├─ /auth-service                       # Auth service
│   │   └─ main.go
│   ├─ /identity-service                   # Identity service
│   │   └─ main.go
│   ├─ /authz-service                      # Authorization service
│   │   └─ main.go
│   ├─ /audit-service                      # Audit service
│   │   └─ main.go
│   └─ /blog-service                       # Blog feature service
│       └─ main.go
│
├─ /services                               # ---- Service Implementations ----
│   ├─ /auth/
│   │   ├─ internal/                       # Service implementation
│   │   └─ api/                            # gRPC/HTTP definitions
│   ├─ /identity/
│   ├─ /authz/
│   ├─ /audit/
│   └─ /blog/
│
├─ /internal                               # ---- Core Kernel (Infrastructure) ----
│   ├─ /config                             # Configuration management
│   ├─ /logger                             # Logging system
│   ├─ /di                                 # Dependency injection
│   ├─ /health                             # Health checks
│   ├─ /metrics                            # Metrics collection
│   ├─ /observability                      # OpenTelemetry integration
│   ├─ /registry                           # Service registry
│   └─ /pluginloader                       # Module loader
│
├─ /pkg                                    # ---- Public Interfaces ----
│   ├─ /config                             # ConfigProvider interface
│   ├─ /logger                             # Logger interface
│   ├─ /services                           # Service client interfaces
│   │   ├─ auth.go                         # AuthServiceClient
│   │   ├─ identity.go                     # IdentityServiceClient
│   │   ├─ authz.go                        # AuthzServiceClient
│   │   └─ audit.go                        # AuditServiceClient
│   └─ /module                             # IModule interface
│
├─ /modules                                # ---- Feature Services ----
│   ├─ /blog/
│   │   ├─ go.mod                          # Service module
│   │   ├─ module.yaml                     # Service manifest
│   │   ├─ internal/                       # Service implementation
│   │   └─ pkg/
│   │       └─ module.go                   # IModule implementation
│   │
│   ├─ /billing/
│   └─ /chat/
│
├─ /infra                                   # ---- Infrastructure Adapters ----
│   ├─ /cache (redis)
│   ├─ /queue (kafka)
│   └─ /storage (s3/azure‑blob)
│
├─ /scripts                                 # build / lint / test helpers
│
├─ /ci
│   └─ github-actions.yml
│
├─ /docs
│   └─ architecture.md
│
├─ go.mod                                  # Workspace root
└─ README.md

How Services Boot

Each service has its own entry point and bootstraps independently:

// cmd/auth-service/main.go
func main() {
    // 1️⃣ Load configuration
    cfg := config.Load()
    
    // 2️⃣ Initialize core kernel (DI, logger, metrics)
    container := di.NewContainer(cfg)
    
    // 3️⃣ Register service implementations
    container.Provide(NewAuthService)
    container.Provide(NewTokenProvider)
    
    // 4️⃣ Register gRPC server
    container.Provide(NewGRPCServer)
    
    // 5️⃣ Register with service registry
    container.Provide(NewServiceRegistry)
    
    // 6️⃣ Start service
    container.Start()
}

// cmd/api-gateway/main.go
func main() {
    // API Gateway bootstraps similarly
    // Routes requests to backend services via service discovery
}

Services communicate via service clients:

• All inter-service communication uses gRPC (primary) or HTTP (fallback)
• Service discovery via service registry
• Each service manages its own database connection
• Services can be deployed independently

---

KEY DECISIONS YOU MUST TAKE EARLY

Decision	Options	Implications
Language / Runtime	Node.js (NestJS, Fastify), Java (Spring Boot), .NET (ASP.NET Core), Go (Gin/Fiber), Python (FastAPI)	Affects DI framework, module packaging, community libs for auth/OIDC, testing.
Persistence Strategy	Relational (PostgreSQL, MySQL) + optional NoSQL (Mongo, Dynamo)	Choose an ORM/Repository pattern that can be swapped per module.
Auth Protocol	JWT + Refresh, OAuth2 Authorization Server, OpenID Connect Provider, or integrate with external IdP (Keycloak, Auth0)	Influences token lifetimes, revocation strategy, multi‑tenant support.
Event Bus	In‑process EventEmitter (for monolith) → Kafka/Rabbit for scaling	Must expose both sync and async hooks.
Module Packaging	NPM packages (private registry) / Maven artifacts / Docker images (for micro‑service extraction)	Define a semantic version policy (core ≥ 1.0.0 never forces breaking changes on plug‑ins).
Multitenancy Model	Single DB with tenant_id column (shared), Schema‑per‑tenant, or DB‑per‑tenant	Affects repository base class and migrations tooling.
Internationalisation	i18next (frontend) + ICU messages in backend, or .NET Resource files	Choose a format that can be merged from modules at build time.
CI/CD	GitHub Actions + Docker Buildx + semantic‑release	Automate publishing of core + modules to same artifact registry.
Testing Strategy	Unit (Jest, JUnit, xUnit), Integration (Testcontainers), Contract (Pact)	Provide a core testing harness that loads a dummy module and asserts the contract of each extension point.

---

COMMON PITFALLS & HOW TO AVOID THEM

Pitfall	Symptoms	Fix / Guardrail
Tight coupling of modules to core implementation	Module imports internal ORM classes, fails on core upgrade.	Expose only interfaces (IUserRepository) from core and keep the concrete implementation as a private package.
Hard‑coded permission strings	Duplicate names across modules, typos cause silent authorisation bypass.	Provide a Permission Builder DSL (Permission.define('blog.post', ['create', 'read'])) that generates constants and registers them automatically.
Global state in modules	Tests interfere with each other, memory leaks when hot‑reloading.	Enforce stateless services; keep per‑request scoped data (e.g., via DI context).
Schema migrations clash	Two modules try to add the same column or foreign key.	Adopt a central migration orchestrator (e.g., Flyway/DBMate) that loads migration scripts from each module in alphabetical order.
Authorization checks omitted in new routes	Security hole for new plug‑in routes.	Provide a base controller class that auto‑applies Authorize filter, or a compile‑time lint rule that checks every exported route for a permission annotation.
Vendor lock‑in to a particular IdP	Hard to replace Keycloak later.	Keep IdP adapters behind a IIdentityProvider interface; ship at least two (local DB + OIDC).
Unbounded background jobs	Queue overflow, OOM, duplicate processing.	Use a job‑scheduler abstraction that caps concurrency, persists state, and provides @Retry decorator.
Insufficient observability	You can’t tell which module caused latency spikes.	Tag every log/metric with module=<moduleName> automatically via middleware.
Version drift between core and modules	Module built against core 1.0 fails on core 1.5.	Publish a core compatibility matrix and enforce peerDependencies in package.json; CI should fail on mismatched ranges.

---

QUICK START GUIDE (What to Build First)

1. Create the Core Kernel

   • Set up DI container, config loader, logger, health/metrics endpoint.
   • Infrastructure only - no business logic.

2. Implement API Gateway

   • Request routing to backend services.
   • Authentication at edge, rate limiting, CORS.
   • Integration with service discovery.

3. Implement Core Services

   • Identity Service: User CRUD, password hashing, email verification.
   • Auth Service: JWT token generation/validation, refresh tokens.
   • Authz Service: Permission resolution, RBAC/ABAC.
   • Audit Service: Immutable audit logging.

4. Set Up Service Communication

   • Define service client interfaces.
   • Implement gRPC clients (primary) and HTTP clients (fallback).
   • Service registry for discovery.

5. Set Up Event Bus & Infrastructure

   • Kafka-based event bus.
   • Redis cache.
   • Shared infrastructure adapters.

6. Build the Module Loader

   • Scan modules/*/module.yaml for service modules.
   • Register services with service registry.
   • Manage service lifecycle.

7. Create a Sample Feature Service – e.g., Blog Service

   • Own entry point (cmd/blog-service/).
   • Own database connection and schema.
   • Use service clients for Auth, Identity, Authz.
   • Define its own entities (Post, Comment).

8. Write Integration Tests

   • Test service interactions via service clients.
   • Spin up services in Docker Compose.
   • Test cross-service communication.

9. Add CI Pipeline

   • Build and test each service independently.
   • Docker images for each service.
   • Service deployment automation.

10. Document Service Architecture

    • Service boundaries and responsibilities.
    • Service client interfaces.
    • Deployment and scaling guides.

---

TOOLS & LIBRARIES (starter suggestions per stack)

Stack	Core	Auth	DI / Module	Event Bus	ORM	Validation	Testing
Node (TypeScript)	NestJS (or Fastify + awilix)	@nestjs/passport, passport-jwt, openid-client	NestJS dynamic modules or @nestjs-modules/mailer	@nestjs/event-emitter or KafkaJS	TypeORM / Prisma	class-validator + class-transformer	Jest + supertest, Testcontainers
Java	Spring Boot	Spring Security + spring-boot-starter-oauth2-resource-server	Spring Boot @Configuration + ImportBeanDefinitionRegistrar	Spring Cloud Stream (Kafka)	JPA / Hibernate	Bean Validation (Hibernate Validator)	JUnit5 + Testcontainers
.NET 8	ASP.NET Core	Microsoft.AspNetCore.Authentication.JwtBearer	IHostedService + Scrutor for module discovery	MassTransit (Rabbit/Kafka)	EF Core	FluentValidation	xUnit + DockerTestContainers
Go	Echo / Fiber	golang.org/x/oauth2 + github.com/golang-jwt/jwt/v5	uber-go/fx for DI, module registration	segmentio/kafka-go	GORM / Ent	go-playground/validator	Testify + Dockertest
Python	FastAPI	fastapi-users / Authlib	pluggy (pytest plugins) or custom loader	aiokafka	SQLModel / Tortoise ORM	Pydantic	Pytest + pytest‑asyncio, Testcontainers

Pick the stack you’re most comfortable with; the concepts stay identical.

---

TL;DR – What You Must Deliver

Layer	Must‑have components	Why
Core Kernel	Config, Logger, DI, Health, Metrics, Error Bus, Observability	Foundation infrastructure for all services.
API Gateway	Request routing, authentication, rate limiting, CORS	Single entry point for all external traffic.
Core Services	Identity, Auth, Authz, Audit services (separate services)	Independent, scalable security services.
Service Clients	gRPC/HTTP clients, service discovery, service registry	Enables service-to-service communication.
Infrastructure Adapters	Cache, Event Bus, Blob storage, Email/SMS, Scheduler	Shared infrastructure capabilities.
Observability	Structured logs, Prometheus metrics, OpenTelemetry traces	Cross-service observability and monitoring.
DevOps Boilerplate	CI pipelines, Dockerfiles, service deployment, Docs	Makes each service production‑ready.
Sample Feature Service	(e.g., Blog Service) with own entry point, DB, service clients	Provides a reference implementation for future services.

When you scaffold those pieces once, any downstream team can drop a new folder that follows the module.yaml contract, implement the initializer, add its own tables & APIs, and instantly get:

• secure authentication,
• role‑based authorization,
• logging/metrics,
• unified config,
• CI‑ready testing,
• optional multi‑tenant isolation.

That’s the foundation of a robust, future‑proof platform boilerplate. Happy building! 🚀