Build the core kernel infrastructure (config, logger, DI, health, metrics, observability) with no business logic. Implement API Gateway as core infrastructure component. Create service client interfaces and service registry foundation. Establish HTTP/gRPC server foundations that services will use.

Note: This epic focuses on infrastructure only. Business services (Auth, Identity, Authz, Audit) are implemented in Epic 2 as separate microservices.

Stories

1.1 Enhanced Dependency Injection Container

Story: 1.1 - Enhanced DI Container
Goal: Extend the DI container to provide core kernel infrastructure services only (no business logic) with proper lifecycle management.
Deliverables: Extended DI container, provider functions for core kernel services only, core module export

1.2 Database Client Foundation

Story: 1.2 - Database Client Foundation
Goal: Set up database client foundation for services. Each service will have its own database connection and schema.
Deliverables: Database client wrapper with schema support, connection pooling, per-service connection management

Note: Core domain entities (User, Role, Permission, AuditLog) are implemented in Epic 2 as part of their respective services.

1.3 Health Monitoring and Metrics System

Story: 1.3 - Health & Metrics
Goal: Implement comprehensive health checks and Prometheus metrics for monitoring platform health and performance.
Deliverables: Health check system, Prometheus metrics, health endpoints, metrics endpoint

1.4 Error Handling and Error Bus

Story: 1.4 - Error Handling
Goal: Implement centralized error handling with an error bus that captures, logs, and optionally reports all application errors.
Deliverables: Error bus interface, channel-based implementation, panic recovery middleware

1.5 HTTP/gRPC Server Foundation

Story: 1.5 - HTTP/gRPC Server Foundation
Goal: Create HTTP and gRPC server foundation that services can use. Each service will have its own server instance.
Deliverables: HTTP server foundation, gRPC server foundation, common middleware, lifecycle management

1.6 OpenTelemetry Distributed Tracing

Story: 1.6 - OpenTelemetry
Goal: Integrate OpenTelemetry for distributed tracing across all services to enable observability in production.
Deliverables: OpenTelemetry setup, HTTP instrumentation, gRPC instrumentation, database instrumentation, trace-log correlation

1.7 Service Client Interfaces

Story: 1.7 - Service Client Interfaces
Goal: Create service client interfaces for all core services to enable microservices communication.
Deliverables: Service client interfaces in pkg/services/, service client factory, gRPC/HTTP client implementations

1.8 API Gateway Implementation

Story: 1.8 - API Gateway
Goal: Implement API Gateway as core infrastructure component that routes all external traffic to backend services.
Deliverables: API Gateway service entry point, gateway implementation with routing, JWT validation, rate limiting, service discovery integration

Deliverables Checklist

DI container with core kernel services only (no business logic)
Database client foundation (per-service connections)
Health and metrics endpoints functional
Error bus captures and logs errors
HTTP/gRPC server foundation for services
Basic observability with OpenTelemetry
Service client interfaces defined
API Gateway service (core infrastructure)
Basic service registry implementation (Consul)

Acceptance Criteria

GET /healthz returns 200 for all services
GET /ready checks service health
GET /metrics exposes Prometheus metrics
Panic recovery logs errors via error bus
HTTP/gRPC requests are traced with OpenTelemetry
API Gateway routes requests to backend services
Service client interfaces are defined
Services can register with Consul
No business logic services in Epic 1

Implementation Summary

Implementation Summary and Verification Instructions - Complete guide on how to verify all Epic 1 functionality, including database testing and Docker Compose setup