Car Rental Microservices System

A distributed car rental platform built with Spring Boot microservices, demonstrating enterprise-grade architecture with clean code principles, SOLID design patterns, and event-driven communication.

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Table of Contents

1. System Architecture
2. Functional Requirements
3. Non-Functional Requirements
4. Technology Stack
5. Project Structure
6. Microservices Overview
7. API Endpoints
8. Layered Architecture
9. Communication Patterns
10. Key Design Patterns
11. Setup & Deployment

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System Architecture

Overall System Design

graph TB
%% Increased spacing between nodes
%% Using padding and line breaks for better visual separation

    Client["🖥️ Client Applications"]

    Client -->|"<span style='color:rgb(255, 127, 80);padding:2px 8px;border:none;background:rgb(15,17,26);'>HTTP</span>"| Gateway["🔗 API Gateway<br/>Spring Cloud Gateway<br/>Port: 9010"]

    Gateway -->|"<span style='background:rgb(15,17,26);color:rgb(26,188,156);padding:2px 8px;border:none;'>Service Discovery</span>"| Discovery["📡 Discovery Server<br/>Eureka<br/>Port: 8761"]

    Gateway -->|"<span style='background:rgb(15,17,26);color:rgb(255, 127, 80);padding:2px 8px;border:none;'>Route</span>"| RentalSvc["🚗 Rental Service<br/>Port: 8081<br/>PostgreSQL"]
    Gateway -->|"<span style='background:rgb(15,17,26);color:rgb(255, 127, 80);padding:2px 8px;border:none;'>Route</span>"| InventorySvc["📦 Inventory Service<br/>Port: 8082<br/>PostgreSQL"]
    Gateway -->|"<span style='background:rgb(15,17,26);color:rgb(255, 127, 80);padding:2px 8px;border:none;'>Route</span>"| FilterSvc["🔍 Filter Service<br/>Port: 8083<br/>MongoDB"]
    Gateway -->|"<span style='background:rgb(15,17,26);color:rgb(255, 127, 80);padding:2px 8px;border:none;'>Route</span>"| PaymentSvc["💳 Payment Service<br/>Port: 8084<br/>PostgreSQL"]
    Gateway -->|"<span style='background:rgb(15,17,26);color:rgb(255, 127, 80);padding:2px 8px;border:none;'>Route</span>"| InvoiceSvc["📄 Invoice Service<br/>Port: 8085<br/>MongoDB"]
    Gateway -->|"<span style='background:rgb(15,17,26);color:rgb(255, 127, 80);padding:2px 8px;border:none;'>Route</span>"| MaintenanceSvc["🔧 Maintenance Service<br/>Port: 8086<br/>MySQL"]

    RentalSvc -->|"<span style='background:rgb(15,17,26);color: rgb(197,52,255);padding:2px 8px;border:none;'>REST/Feign<br/>Retry Pattern</span>"| InventorySvc
    RentalSvc -->|"<span style='background:rgb(15,17,26);color: rgb(197,52,255);padding:2px 8px;border:none;'>REST/Feign</span>"| PaymentSvc
    MaintenanceSvc -->|"<span style='background:rgb(15,17,26);color:rgb(0,255,238);padding:2px 8px;border:none;'>REST/Feign</span>"| InventorySvc

    RentalSvc -->|"<span style='background:rgb(15,17,26);color: rgb(197,52,255);padding:2px 8px;border:none;'>Kafka Event</span>"| Kafka["📨 Kafka<br/>Port: 9092"]
    MaintenanceSvc -->|"<span style='background:rgb(15,17,26);color:rgb(0,255,238);padding:2px 8px;border:none;'>Kafka Event</span>"| Kafka
    InventorySvc -->|"<span style='background:rgb(15,17,26);color:rgb(240,204,0);padding:2px 8px;border:none;'>Kafka Event</span>"| Kafka

    Kafka -->|"<span style='background:rgb(15,17,26);color:rgb(225,55,122);padding:2px 8px;border:none;'>Consume</span>"| FilterSvc
    Kafka -->|"<span style='background:rgb(15,17,26);color:rgb(225,55,122);padding:2px 8px;border:none;'>Consume</span>"| InvoiceSvc
    Kafka -->|"<span style='background:rgb(15,17,26);color:rgb(225,55,122);padding:2px 8px;border:none;'>Consume</span>"| InventorySvc

    RentalSvc -->|"<span style='background:rgb(15,17,26);color: rgb(197,52,255);padding:2px 8px;border:none;'>Auth/OAuth2</span>"| Keycloak["🔐 Keycloak<br/>Port: 8080"]
    InventorySvc -->|"<span style='background:rgb(15,17,26);color:rgb(240,204,0);padding:2px 8px;border:none;'>Auth/OAuth2</span>"| Keycloak
    MaintenanceSvc -->|"<span style='background:rgb(15,17,26);color:rgb(0,255,238);padding:2px 8px;border:none;'>Auth/OAuth2</span>"| Keycloak

    RentalSvc -->|"<span style='background:rgb(15,17,26);color: rgb(197,52,255);padding:2px 8px;border:none;'>Traces</span>"| Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
    InventorySvc -->|"<span style='background:rgb(15,17,26);color:rgb(240,204,0);padding:2px 8px;border:none;'>Traces</span>"| Zipkin
    PaymentSvc -->|"<span style='background:rgb(15,17,26);color:rgb(0,242,60);padding:2px 8px;border:none;'>Traces</span>"| Zipkin
    MaintenanceSvc -->|"<span style='background:rgb(15,17,26);color:rgb(0,255,238);padding:2px 8px;border:none;'>Traces</span>"| Zipkin

    RentalSvc -->|"<span style='background:rgb(15,17,26);color: rgb(197,52,255);padding:2px 8px;border:none;'>Metrics</span>"| Prometheus["📊 Prometheus<br/>Port: 9090"]
    InventorySvc -->|"<span style='background:rgb(15,17,26);color:rgb(240, 204, 0);padding:2px 8px;border:none;'>Metrics</span>"| Prometheus
    PaymentSvc -->|"<span style='background:rgb(15,17,26);color:rgb(0,242,60);padding:2px 8px;border:none;'>Metrics</span>"| Prometheus
    MaintenanceSvc -->|"<span style='background:rgb(15,17,26);color:rgb(0,255,238);padding:2px 8px;border:none;'>Metrics</span>"| Prometheus

    Prometheus -->|"<span style='background:rgb(15,17,26);color:rgb(26,129,255);padding:2px 8px;border:none;'>Visualize</span>"| Grafana["📈 Grafana<br/>Port: 3000"]

    ConfigServer["⚙️ Config Server<br/>Spring Cloud Config<br/>Port: 8888"]
    ConfigServer -->|"<span style='background:rgb(15,17,26);color:rgb(48, 172, 255);padding:2px 8px;border:none;'>Config</span>"| RentalSvc
    ConfigServer -->|"<span style='background:rgb(15,17,26);color:rgb(48, 172, 255);padding:2px 8px;border:none;'>Config</span>"| InventorySvc
    ConfigServer -->|"<span style='background:rgb(15,17,26);color:rgb(48, 172, 255);padding:2px 8px;border:none;'>Config</span>"| FilterSvc
    ConfigServer -->|"<span style='background:rgb(15,17,26);color:rgb(48, 172, 255);padding:2px 8px;border:none;'>Config</span>"| PaymentSvc
    ConfigServer -->|"<span style='background:rgb(15,17,26);color:rgb(48, 172, 255);padding:2px 8px;border:none;'>Config</span>"| InvoiceSvc
    ConfigServer -->|"<span style='background:rgb(15,17,26);color:rgb(48, 172, 255);padding:2px 8px;border:none;'>Config</span>"| MaintenanceSvc

%% Node Styles with better contrast
    style Client fill:#FF7F50,color:#FFFFFF,stroke:#1A252F,stroke-width:2px
    style Gateway fill:#E74C3C,color:#FFFFFF,stroke:#C0392B,stroke-width:2px
    style Discovery fill:#1ABC9C,color:#FFFFFF,stroke:#16A085,stroke-width:2px
    style ConfigServer fill:#008AE7,color:#FFFFFF,stroke:#2980B9,stroke-width:2px
    style Kafka fill:#D50047,color:#FFFFFF,stroke:#8E0038,stroke-width:2px
    style Keycloak fill:#2ECC71,color:#FFFFFF,stroke:#27AE60,stroke-width:2px
    style Zipkin fill:#E74C3C,color:#FFFFFF,stroke:#C0392B,stroke-width:2px
    style Prometheus fill:#3B00EE,color:#FFFFFF,stroke:#24009A,stroke-width:2px
    style Grafana fill:#D35400,color:#FFFFFF,stroke:#A04000,stroke-width:2px

%% Service Nodes with better contrast
    style RentalSvc fill:#7C00AD,color:#FFFFFF,stroke:#5A007D,stroke-width:2px
    style InventorySvc fill:#F0CC00,color:#000000,stroke:#B8860B,stroke-width:2px
    style FilterSvc fill:#F4D03F,color:#1C2833,stroke:#D4AC0D,stroke-width:2px
    style PaymentSvc fill:#00D435,color:#FFFFFF,stroke:#008F26,stroke-width:2px
    style InvoiceSvc fill:#5D6D7E,color:#FFFFFF,stroke:#2E4053,stroke-width:2px
    style MaintenanceSvc fill:#00FFEE,color:#000000,stroke:#008B8B,stroke-width:2px

%% Arrow styles with matching colors
    linkStyle 1 stroke:#1ABC9C,stroke-width:3px
    linkStyle 0 stroke:#E74C3C,stroke-width:3px
    linkStyle 2 stroke:#E74C3C,stroke-width:3px
    linkStyle 3 stroke:#E74C3C,stroke-width:3px
    linkStyle 4 stroke:#E74C3C,stroke-width:3px
    linkStyle 5 stroke:#E74C3C,stroke-width:3px
    linkStyle 6 stroke:#E74C3C,stroke-width:3px
    linkStyle 7 stroke:#E74C3C,stroke-width:3px
    linkStyle 8 stroke:#7C00AD,stroke-width:3px
    linkStyle 9 stroke:#7C00AD,stroke-width:3px
    linkStyle 11 stroke:#7C00AD,stroke-width:3px
    linkStyle 17 stroke:#7C00AD,stroke-width:3px
    linkStyle 20 stroke:#7C00AD,stroke-width:3px
    linkStyle 24 stroke:#7C00AD,stroke-width:3px
    linkStyle 18 stroke:#F0CC00,stroke-width:3px
    linkStyle 13 stroke:#F0CC00,stroke-width:3px
    linkStyle 25 stroke:#F0CC00,stroke-width:3px
    linkStyle 21 stroke:#F0CC00,stroke-width:3px
    linkStyle 14 stroke:#D50047,stroke-width:3px
    linkStyle 15 stroke:#D50047,stroke-width:3px
    linkStyle 16 stroke:#D50047,stroke-width:3px
    linkStyle 23 stroke:#00FFEE,stroke-width:3px
    linkStyle 27 stroke:#00FFEE,stroke-width:3px
    linkStyle 12 stroke:#00FFEE,stroke-width:3px
    linkStyle 19 stroke:#00FFEE,stroke-width:3px
    linkStyle 10 stroke:#00FFEE,stroke-width:3px
    linkStyle 26 stroke:#00D435,stroke-width:3px
    linkStyle 22 stroke:#00D435,stroke-width:3px
    linkStyle 28 stroke:#3498DB,stroke-width:3px
    linkStyle 29 stroke:#008AE7,stroke-width:3px
    linkStyle 30 stroke:#008AE7,stroke-width:3px
    linkStyle 31 stroke:#008AE7,stroke-width:3px
    linkStyle 32 stroke:#008AE7,stroke-width:3px
    linkStyle 33 stroke:#008AE7,stroke-width:3px
    linkStyle 34 stroke:#008AE7,stroke-width:3px

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The system follows a microservices decomposed by business capability pattern with:

• Single API Gateway entry point
• Service discovery via Eureka
• Centralized configuration management
• Asynchronous event-driven communication via Kafka
• Distributed tracing and monitoring

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Functional Requirements

✅ Admin Capabilities

• Register system administrators
• Add, update, and manage vehicles (brands, models, cars)
• Change vehicle pricing and details
• View all rental transactions
• Send vehicles for maintenance
• Add new vehicle tools/features to the system

✅ User Capabilities

• Browse and filter vehicles by features
• Check real-time vehicle availability
• Rent desired vehicles with immediate confirmation
• Process payments via multiple payment methods
• View current and historical rental transactions
• Access current and past invoices

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Non-Functional Requirements

Requirement	Implementation
Low Latency	Asynchronous Kafka events + optimized REST calls with Feign
High Availability	Distributed services, load balancing via API Gateway
Consistency	Eventual consistency via Kafka; strong consistency for critical operations
Scalability	Horizontal scaling, containerized services, random port allocation
Concurrency	Concurrent rental handling via microservices isolation

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Technology Stack

Core Framework

• Spring Boot 3.x - Microservices foundation
• Spring Cloud 2022.0.2 - Distributed systems support
• Java 17 - Language runtime

API & Communication

• Spring Cloud Gateway - API Gateway routing
• OpenFeign - Declarative REST client
• Resilience4j - Retry pattern implementation
• Kafka - Asynchronous event streaming

Service Discovery & Configuration

• Eureka - Service registry & discovery
• Spring Cloud Config - Centralized configuration management

Data Access

• Spring Data JPA - ORM with Hibernate
• PostgreSQL - Transactional databases (Rental, Inventory, Payment)
• MySQL - Maintenance service database
• MongoDB - Read-optimized caches (Filter, Invoice)

Security & Authentication

• Keycloak - OAuth2/OIDC authentication & authorization
• Spring Security - Authorization framework

Observability

• Zipkin - Distributed tracing
• Prometheus - Metrics collection
• Grafana - Metrics visualization
• SLF4J - Structured logging

Development Tools

• Lombok - Reduce boilerplate code
• ModelMapper - DTO transformations
• Docker - Containerization
• Maven - Build management

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Project Structure

car-rent-microservices/
├── api-gateway/                 # Spring Cloud Gateway routing
├── config-server/               # Centralized configuration
├── discovery-server/            # Eureka service registry
├── common-package/              # Shared libraries & utilities
├── rental-service/              # User rental transactions
├── inventory-service/           # Admin vehicle management
├── filter-service/              # User vehicle search & filtering
├── payment-service/             # Payment processing & records
├── invoice-service/             # Invoice storage & retrieval
├── maintenance-service/         # Vehicle maintenance management
└── docker-compose.yml           # Infrastructure setup

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Microservices Overview

1. API Gateway (Port: 9010)

Entry point for all external requests. Routes requests to appropriate microservices using Eureka service discovery.

graph TB
    Client["🖥️ External Clients"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Routing Configuration"
        Route1["Route: /api/rentals/**<br/>→ Rental Service:8081"]
        Route2["Route: /api/brands/**<br/>→ Inventory Service:8082"]
        Route3["Route: /api/models/**<br/>→ Inventory Service:8082"]
        Route4["Route: /api/cars/**<br/>→ Inventory Service:8082"]
        Route5["Route: /api/filters/**<br/>→ Filter Service:8083"]
        Route6["Route: /api/payments/**<br/>→ Payment Service:8084"]
        Route7["Route: /api/invoices/**<br/>→ Invoice Service:8085"]
        Route8["Route: /api/maintenances/**<br/>→ Maintenance Service:8086"]
    end

    subgraph "Service Discovery"
        Eureka["📡 Eureka<br/>Port: 8761<br/>Service Lookup"]
    end

%% Client to Gateway
    Client -->|HTTP Requests| Gateway

%% Gateway discovers services
    Gateway -->|Service Lookup| Eureka

%% Routes
    Gateway -->|Apply Route| Route1
    Gateway -->|Apply Route| Route2
    Gateway -->|Apply Route| Route3
    Gateway -->|Apply Route| Route4
    Gateway -->|Apply Route| Route5
    Gateway -->|Apply Route| Route6
    Gateway -->|Apply Route| Route7
    Gateway -->|Apply Route| Route8

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff
    style Route1 fill:#90EE90,stroke:#52B788,color:#000
    style Route2 fill:#90EE90,stroke:#52B788,color:#000
    style Route3 fill:#90EE90,stroke:#52B788,color:#000
    style Route4 fill:#90EE90,stroke:#52B788,color:#000
    style Route5 fill:#90EE90,stroke:#52B788,color:#000
    style Route6 fill:#90EE90,stroke:#52B788,color:#000
    style Route7 fill:#90EE90,stroke:#52B788,color:#000
    style Route8 fill:#90EE90,stroke:#52B788,color:#000
    style Eureka fill:#4ECDC4,stroke:#45B7D1,color:#000

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Responsibilities:

• Request routing based on URL patterns
• Service discovery from Eureka
• Load balancing

---

2. Discovery Server - Eureka (Port: 8761)

Central service registry where all microservices register themselves and publish health status.

graph TB
    subgraph "Eureka Discovery Server"
        Eureka["📡 Eureka Server<br/>Port: 8761<br/>Service Registry"]
    end

    subgraph "Service Registration"
        RentalReg["Rental Service<br/>Port: 8081<br/>Instance: rental-service"]
        InventoryReg["Inventory Service<br/>Port: 8082<br/>Instance: inventory-service"]
        FilterReg["Filter Service<br/>Port: 8083<br/>Instance: filter-service"]
        PaymentReg["Payment Service<br/>Port: 8084<br/>Instance: payment-service"]
        InvoiceReg["Invoice Service<br/>Port: 8085<br/>Instance: invoice-service"]
        MaintenanceReg["Maintenance Service<br/>Port: 8086<br/>Instance: maintenance-service"]
    end

    subgraph "Service Discovery Clients"
        GatewayClient["API Gateway<br/>Looks up services<br/>Load balancing"]
    end

%% Services register with Eureka
    RentalReg -->|Register/Heartbeat| Eureka
    InventoryReg -->|Register/Heartbeat| Eureka
    FilterReg -->|Register/Heartbeat| Eureka
    PaymentReg -->|Register/Heartbeat| Eureka
    InvoiceReg -->|Register/Heartbeat| Eureka
    MaintenanceReg -->|Register/Heartbeat| Eureka

%% Gateway queries Eureka
    GatewayClient -->|Query Service List| Eureka
    Eureka -->|Return Available Services| GatewayClient

%% Styling
    style Eureka fill:#4ECDC4,stroke:#45B7D1,color:#000
    style RentalReg fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style InventoryReg fill:#27AE60,stroke:#1E8449,color:#fff
    style FilterReg fill:#4A90E2,stroke:#3B73C4,color:#fff
    style PaymentReg fill:#8E44AD,stroke:#6C3483,color:#fff
    style InvoiceReg fill:#4A90E2,stroke:#3B73C4,color:#fff
    style MaintenanceReg fill:#FFB347,stroke:#E67E22,color:#fff
    style GatewayClient fill:#FF6B6B,stroke:#C92A2A,color:#fff

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Responsibilities:

• Service registration and deregistration
• Health check monitoring via heartbeats
• Service lookup for dynamic routing

---

3. Config Server (Port: 8888)

Manages centralized configuration for all microservices from Git repository.

graph TB
    subgraph "Config Server"
        ConfigServer["⚙️ Spring Cloud Config Server<br/>Port: 8888<br/>Centralized Configuration"]
    end

    subgraph "Configuration Sources"
        GitRepo["Git Repository<br/>application-dev.yml<br/>application-prod.yml<br/>application.yml"]
    end

    subgraph "Config Clients"
        RentalSvc["🚗 Rental Service<br/>Port: 8081<br/>Fetches config"]
        InventorySvc["📦 Inventory Service<br/>Port: 8082<br/>Fetches config"]
        FilterSvc["🔍 Filter Service<br/>Port: 8083<br/>Fetches config"]
        PaymentSvc["💳 Payment Service<br/>Port: 8084<br/>Fetches config"]
        InvoiceSvc["📄 Invoice Service<br/>Port: 8085<br/>Fetches config"]
        MaintenanceSvc["🔧 Maintenance Service<br/>Port: 8086<br/>Fetches config"]
    end

%% Config Server reads from Git
    ConfigServer -->|Read Configs| GitRepo

%% Services fetch from Config Server
    RentalSvc -->|Fetch Config| ConfigServer
    InventorySvc -->|Fetch Config| ConfigServer
    FilterSvc -->|Fetch Config| ConfigServer
    PaymentSvc -->|Fetch Config| ConfigServer
    InvoiceSvc -->|Fetch Config| ConfigServer
    MaintenanceSvc -->|Fetch Config| ConfigServer

%% Styling
    style ConfigServer fill:#45B7D1,stroke:#3498DB,color:#fff
    style GitRepo fill:#333333,stroke:#000000,color:#fff
    style RentalSvc fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style InventorySvc fill:#27AE60,stroke:#1E8449,color:#fff
    style FilterSvc fill:#4A90E2,stroke:#3B73C4,color:#fff
    style PaymentSvc fill:#8E44AD,stroke:#6C3483,color:#fff
    style InvoiceSvc fill:#4A90E2,stroke:#3B73C4,color:#fff
    style MaintenanceSvc fill:#FFB347,stroke:#E67E22,color:#fff

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Responsibilities:

• Pull configuration from Git
• Serve environment-specific configs (Dev/Prod)
• Dynamic configuration updates

---

4. Rental Service (Port: 8081)

User-facing microservice for managing car rental transactions with payment processing and invoice generation.

Database: PostgreSQL

Endpoints:

graph TB
    Client["🖥️ Client/User"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Rental Service"
        GetAll["<b>GET /api/rentals</b><br/>Fetch all rentals"]
        GetById["<b>GET /api/rentals/{id}</b><br/>Fetch specific rental"]
        Create["<b>POST /api/rentals</b><br/>Create new rental<br/>& process payment"]
        Update["<b>PUT /api/rentals/{id}</b><br/>Update rental record"]
        Delete["<b>DELETE /api/rentals/{id}</b><br/>Delete rental record"]

        RentalController["RentalController<br/>Handles 5 endpoints"]
        RentalSvc["🚗 RentalService<br/>Business Logic<br/>Orchestrates transactions"]
    end

    subgraph "Database"
        PostgreSQL["🗄️ PostgreSQL<br/>rental_db<br/>Port: 5432"]
    end

    subgraph "Service-to-Service Communication"
        CarClient["CarClient<br/>@FeignClient<br/>@Retry"]
        CheckAvail["<b>GET /api/cars/check-car-available/{carId}</b><br/>Verify car availability"]
        GetCarInv["<b>GET /api/cars/get-car-for-invoice/{carId}</b><br/>Fetch car details for invoice"]
    end

    subgraph "Inventory Service"
        InventorySvc["📦 Inventory Service<br/>Port: 8082<br/>Resilience4j Retry"]
    end

    subgraph "Payment Communication"
        PaymentClient["PaymentClient<br/>@FeignClient"]
        ProcessPayment["<b>POST /api/payments/process-rental-payment</b><br/>Process payment"]
    end

    subgraph "Payment Service"
        PaymentSvc["💳 Payment Service<br/>Port: 8084"]
    end

    subgraph "Event Bus"
        Kafka["📨 Kafka<br/>Event Streaming<br/>Port: 9092"]
    end

    subgraph "Event Consumers"
        InvoiceSvc["📄 Invoice Service<br/>Creates invoices"]
        InventoryEventSvc["📦 Inventory Service<br/>Updates car availability"]
    end

    subgraph "Infrastructure"
        Keycloak["🔐 Keycloak<br/>Authentication<br/>Port: 8080"]
        Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
        Prometheus["📊 Prometheus<br/>Metrics<br/>Port: 9090"]
    end

%% Client to Gateway
    Client -->|HTTP Request| Gateway

%% Gateway to Controller
    Gateway -->|Route| RentalController

%% Controller to Endpoints
    RentalController -->|1. GET| GetAll
    RentalController -->|2. GET| GetById
    RentalController -->|3. POST| Create
    RentalController -->|4. PUT| Update
    RentalController -->|5. DELETE| Delete

%% Endpoints to Service
    GetAll -->|Process| RentalSvc
    GetById -->|Process| RentalSvc
    Create -->|Process| RentalSvc
    Update -->|Process| RentalSvc
    Delete -->|Process| RentalSvc

%% Service to Database
    RentalSvc -->|CRUD Operations| PostgreSQL

%% Feign Client - Inventory Service
    RentalSvc -->|REST/Feign<br/>Retry Pattern| CarClient
    CarClient -->|Check availability| CheckAvail
    CheckAvail -->|GET call| InventorySvc
    CarClient -->|Get car details| GetCarInv
    GetCarInv -->|GET call| InventorySvc

%% Feign Client - Payment Service
    RentalSvc -->|REST/Feign| PaymentClient
    PaymentClient -->|Process payment| ProcessPayment
    ProcessPayment -->|POST call| PaymentSvc

%% Kafka Events Publishing
    RentalSvc -->|Publish Events<br/>rental_created<br/>rental_completed<br/>rental_invoice_created| Kafka

%% Event Consumers
    Kafka -->|Consume rental events| InvoiceSvc
    Kafka -->|Consume rental events| InventoryEventSvc

%% Infrastructure Integrations
    RentalController -->|OAuth2/JWT| Keycloak
    RentalSvc -->|Send Traces| Zipkin
    RentalSvc -->|Expose Metrics| Prometheus

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style RentalController fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style RentalSvc fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style GetAll fill:#90EE90,stroke:#52B788,color:#000
    style GetById fill:#90EE90,stroke:#52B788,color:#000
    style Create fill:#87CEEB,stroke:#4A90E2,color:#000
    style Update fill:#F0E68C,stroke:#F39C12,color:#000
    style Delete fill:#FFB6C1,stroke:#E74C3C,color:#000
    style PostgreSQL fill:#336791,stroke:#0E4C92,color:#fff
    style CarClient fill:#FF6B00,stroke:#CC5500,color:#fff
    style CheckAvail fill:#FFA500,stroke:#D97706,color:#000
    style GetCarInv fill:#FFA500,stroke:#D97706,color:#000
    style InventorySvc fill:#27AE60,stroke:#1E8449,color:#fff
    style PaymentClient fill:#9B59B6,stroke:#7D3C98,color:#fff
    style ProcessPayment fill:#DDA0DD,stroke:#9B59B6,color:#000
    style PaymentSvc fill:#8E44AD,stroke:#6C3483,color:#fff
    style Kafka fill:#FFE66D,stroke:#F1C40F,color:#000
    style InvoiceSvc fill:#4A90E2,stroke:#3B73C4,color:#fff
    style InventoryEventSvc fill:#27AE60,stroke:#1E8449,color:#fff
    style Keycloak fill:#95E1D3,stroke:#16A085,color:#000
    style Zipkin fill:#F38181,stroke:#E74C3C,color:#fff
    style Prometheus fill:#AA96DA,stroke:#8E44AD,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff

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Key Features:

• Create rental transactions
• Process payments via Payment Service
• Check car availability via Inventory Service
• Publish rental events to Kafka
• Implements Retry pattern for resilience

API:

• GET /api/rentals - Fetch all rentals
• GET /api/rentals/{id} - Fetch specific rental
• POST /api/rentals - Create new rental (with payment)
• PUT /api/rentals/{id} - Update rental
• DELETE /api/rentals/{id} - Delete rental

---

5. Inventory Service (Port: 8082)

Admin-facing microservice for managing vehicle brands, models, and car inventory.

Database: PostgreSQL

Endpoints divided into 3 resource types:

Brands Management

graph TB
    Client["🖥️ Client/Admin"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Inventory Service - Brands"
        GetAll["<b>GET /api/brands</b><br/>Fetch all brands"]
        GetById["<b>GET /api/brands/{id}</b><br/>Fetch specific brand"]
        Create["<b>POST /api/brands</b><br/>Create new brand"]
        Update["<b>PUT /api/brands/{id}</b><br/>Update brand"]
        Delete["<b>DELETE /api/brands/{id}</b><br/>Delete brand"]

        BrandController["BrandController<br/>Handles 5 endpoints"]
        BrandSvc["📦 BrandService<br/>Business Logic"]
    end

    subgraph "Database"
        PostgreSQL["🗄️ PostgreSQL<br/>inventory_db<br/>Port: 5432"]
    end

    subgraph "Event Bus"
        Kafka["📨 Kafka<br/>Event Streaming<br/>Port: 9092"]
    end

    subgraph "Event Consumers"
        FilterSvc["🔍 Filter Service<br/>Updates brand data"]
    end

    subgraph "Infrastructure"
        Keycloak["🔐 Keycloak<br/>Authentication<br/>Port: 8080"]
        Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
        Prometheus["📊 Prometheus<br/>Metrics<br/>Port: 9090"]
    end

%% Client to Gateway
    Client -->|HTTP Request| Gateway

%% Gateway to Controller
    Gateway -->|Route| BrandController

%% Controller to Endpoints
    BrandController -->|1. GET| GetAll
    BrandController -->|2. GET| GetById
    BrandController -->|3. POST| Create
    BrandController -->|4. PUT| Update
    BrandController -->|5. DELETE| Delete

%% Endpoints to Service
    GetAll -->|Process| BrandSvc
    GetById -->|Process| BrandSvc
    Create -->|Process| BrandSvc
    Update -->|Process| BrandSvc
    Delete -->|Process| BrandSvc

%% Service to Database
    BrandSvc -->|CRUD Operations| PostgreSQL

%% Kafka Events Publishing
    BrandSvc -->|Publish Events<br/>brand_created<br/>brand_updated<br/>brand_deleted| Kafka

%% Event Consumers
    Kafka -->|Consume brand events| FilterSvc

%% Infrastructure Integrations
    BrandController -->|OAuth2/JWT| Keycloak
    BrandSvc -->|Send Traces| Zipkin
    BrandSvc -->|Expose Metrics| Prometheus

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style BrandController fill:#27AE60,stroke:#1E8449,color:#fff
    style BrandSvc fill:#27AE60,stroke:#1E8449,color:#fff
    style GetAll fill:#90EE90,stroke:#52B788,color:#000
    style GetById fill:#90EE90,stroke:#52B788,color:#000
    style Create fill:#87CEEB,stroke:#4A90E2,color:#000
    style Update fill:#F0E68C,stroke:#F39C12,color:#000
    style Delete fill:#FFB6C1,stroke:#E74C3C,color:#000
    style PostgreSQL fill:#336791,stroke:#0E4C92,color:#fff
    style Kafka fill:#FFE66D,stroke:#F1C40F,color:#000
    style FilterSvc fill:#4A90E2,stroke:#3B73C4,color:#fff
    style Keycloak fill:#95E1D3,stroke:#16A085,color:#000
    style Zipkin fill:#F38181,stroke:#E74C3C,color:#fff
    style Prometheus fill:#AA96DA,stroke:#8E44AD,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff

Loading

• GET /api/brands - Fetch all brands
• GET /api/brands/{id} - Fetch specific brand
• POST /api/brands - Create brand
• PUT /api/brands/{id} - Update brand
• DELETE /api/brands/{id} - Delete brand

Models Management

graph TB
    Client["🖥️ Client/Admin"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Inventory Service - Models"
        GetAll["<b>GET /api/models</b><br/>Fetch all models"]
        GetById["<b>GET /api/models/{id}</b><br/>Fetch specific model"]
        Create["<b>POST /api/models</b><br/>Create new model"]
        Update["<b>PUT /api/models/{id}</b><br/>Update model"]
        Delete["<b>DELETE /api/models/{id}</b><br/>Delete model"]

        ModelController["ModelController<br/>Handles 5 endpoints"]
        ModelSvc["📦 ModelService<br/>Business Logic"]
    end

    subgraph "Database"
        PostgreSQL["🗄️ PostgreSQL<br/>inventory_db<br/>Port: 5432"]
    end

    subgraph "Event Bus"
        Kafka["📨 Kafka<br/>Event Streaming<br/>Port: 9092"]
    end

    subgraph "Event Consumers"
        FilterSvc["🔍 Filter Service<br/>Updates model data"]
    end

    subgraph "Infrastructure"
        Keycloak["🔐 Keycloak<br/>Authentication<br/>Port: 8080"]
        Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
        Prometheus["📊 Prometheus<br/>Metrics<br/>Port: 9090"]
    end

%% Client to Gateway
    Client -->|HTTP Request| Gateway

%% Gateway to Controller
    Gateway -->|Route| ModelController

%% Controller to Endpoints
    ModelController -->|1. GET| GetAll
    ModelController -->|2. GET| GetById
    ModelController -->|3. POST| Create
    ModelController -->|4. PUT| Update
    ModelController -->|5. DELETE| Delete

%% Endpoints to Service
    GetAll -->|Process| ModelSvc
    GetById -->|Process| ModelSvc
    Create -->|Process| ModelSvc
    Update -->|Process| ModelSvc
    Delete -->|Process| ModelSvc

%% Service to Database
    ModelSvc -->|CRUD Operations| PostgreSQL

%% Kafka Events Publishing
    ModelSvc -->|Publish Events<br/>model_created<br/>model_updated<br/>model_deleted| Kafka

%% Event Consumers
    Kafka -->|Consume model events| FilterSvc

%% Infrastructure Integrations
    ModelController -->|OAuth2/JWT| Keycloak
    ModelSvc -->|Send Traces| Zipkin
    ModelSvc -->|Expose Metrics| Prometheus

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style ModelController fill:#3498DB,stroke:#2980B9,color:#fff
    style ModelSvc fill:#3498DB,stroke:#2980B9,color:#fff
    style GetAll fill:#90EE90,stroke:#52B788,color:#000
    style GetById fill:#90EE90,stroke:#52B788,color:#000
    style Create fill:#87CEEB,stroke:#4A90E2,color:#000
    style Update fill:#F0E68C,stroke:#F39C12,color:#000
    style Delete fill:#FFB6C1,stroke:#E74C3C,color:#000
    style PostgreSQL fill:#336791,stroke:#0E4C92,color:#fff
    style Kafka fill:#FFE66D,stroke:#F1C40F,color:#000
    style FilterSvc fill:#4A90E2,stroke:#3B73C4,color:#fff
    style Keycloak fill:#95E1D3,stroke:#16A085,color:#000
    style Zipkin fill:#F38181,stroke:#E74C3C,color:#fff
    style Prometheus fill:#AA96DA,stroke:#8E44AD,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff

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• GET /api/models - Fetch all models
• GET /api/models/{id} - Fetch specific model
• POST /api/models - Create model
• PUT /api/models/{id} - Update model
• DELETE /api/models/{id} - Delete model

Cars Management

graph TB
    Client["🖥️ Client/Admin"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Inventory Service - Cars"
        GetAll["<b>GET /api/cars</b><br/>Fetch all cars"]
        GetById["<b>GET /api/cars/{id}</b><br/>Fetch specific car"]
        Create["<b>POST /api/cars</b><br/>Create new car"]
        Update["<b>PUT /api/cars/{id}</b><br/>Update car"]
        Delete["<b>DELETE /api/cars/{id}</b><br/>Delete car"]
        CheckAvail["<b>GET /api/cars/check-car-available/{id}</b><br/>Check car availability"]
        GetInvoice["<b>GET /api/cars/get-car-for-invoice/{carId}</b><br/>Get car for invoice"]

        CarController["CarController<br/>Handles 7 endpoints"]
        CarSvc["🚗 CarService<br/>Business Logic"]
    end

    subgraph "Database"
        PostgreSQL["🗄️ PostgreSQL<br/>inventory_db<br/>Port: 5432"]
    end

    subgraph "Internal REST Clients"
        RentalClient["Called by<br/>Rental Service<br/>@FeignClient"]
        MaintenanceClient["Called by<br/>Maintenance Service<br/>@FeignClient"]
        InvoiceClient["Called by<br/>Invoice Service<br/>@FeignClient"]
    end

    subgraph "Event Bus"
        Kafka["📨 Kafka<br/>Event Streaming<br/>Port: 9092"]
    end

    subgraph "Event Consumers"
        FilterSvc["🔍 Filter Service<br/>Updates car availability"]
    end

    subgraph "Infrastructure"
        Keycloak["🔐 Keycloak<br/>Authentication<br/>Port: 8080"]
        Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
        Prometheus["📊 Prometheus<br/>Metrics<br/>Port: 9090"]
    end

%% Client to Gateway
    Client -->|HTTP Request| Gateway

%% Gateway to Controller
    Gateway -->|Route| CarController

%% Controller to Endpoints
    CarController -->|1. GET| GetAll
    CarController -->|2. GET| GetById
    CarController -->|3. POST| Create
    CarController -->|4. PUT| Update
    CarController -->|5. DELETE| Delete
    CarController -->|6. GET| CheckAvail
    CarController -->|7. GET| GetInvoice

%% Endpoints to Service
    GetAll -->|Process| CarSvc
    GetById -->|Process| CarSvc
    Create -->|Process| CarSvc
    Update -->|Process| CarSvc
    Delete -->|Process| CarSvc
    CheckAvail -->|Process| CarSvc
    GetInvoice -->|Process| CarSvc

%% Service to Database
    CarSvc -->|CRUD Operations| PostgreSQL

%% Internal Feign Calls
    RentalClient -->|Calls| CheckAvail
    RentalClient -->|Calls| GetInvoice
    MaintenanceClient -->|Calls| CheckAvail
    InvoiceClient -->|Calls| GetInvoice

%% Kafka Events Publishing
    CarSvc -->|Publish Events<br/>car_created<br/>car_updated<br/>car_deleted<br/>car_availability_changed| Kafka

%% Event Consumers
    Kafka -->|Consume car events| FilterSvc

%% Infrastructure Integrations
    CarController -->|OAuth2/JWT| Keycloak
    CarSvc -->|Send Traces| Zipkin
    CarSvc -->|Expose Metrics| Prometheus

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style CarController fill:#E74C3C,stroke:#C0392B,color:#fff
    style CarSvc fill:#E74C3C,stroke:#C0392B,color:#fff
    style GetAll fill:#90EE90,stroke:#52B788,color:#000
    style GetById fill:#90EE90,stroke:#52B788,color:#000
    style Create fill:#87CEEB,stroke:#4A90E2,color:#000
    style Update fill:#F0E68C,stroke:#F39C12,color:#000
    style Delete fill:#FFB6C1,stroke:#E74C3C,color:#000
    style CheckAvail fill:#FFA500,stroke:#D97706,color:#000
    style GetInvoice fill:#FFA500,stroke:#D97706,color:#000
    style PostgreSQL fill:#336791,stroke:#0E4C92,color:#fff
    style RentalClient fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style MaintenanceClient fill:#FFB347,stroke:#E67E22,color:#fff
    style InvoiceClient fill:#4A90E2,stroke:#3B73C4,color:#fff
    style Kafka fill:#FFE66D,stroke:#F1C40F,color:#000
    style FilterSvc fill:#4A90E2,stroke:#3B73C4,color:#fff
    style Keycloak fill:#95E1D3,stroke:#16A085,color:#000
    style Zipkin fill:#F38181,stroke:#E74C3C,color:#fff
    style Prometheus fill:#AA96DA,stroke:#8E44AD,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff

Loading

• GET /api/cars - Fetch all cars
• GET /api/cars/{id} - Fetch specific car
• POST /api/cars - Add new car
• PUT /api/cars/{id} - Update car details
• DELETE /api/cars/{id} - Delete car
• GET /api/cars/check-car-available/{id} - Check availability (used by Rental & Maintenance)
• GET /api/cars/get-car-for-invoice/{carId} - Get car details for invoicing

Key Features:

• Complete CRUD for brands, models, and cars
• Publish inventory change events to Kafka
• Internal endpoints for inter-service communication

---

6. Filter Service (Port: 8083)

User-facing read-optimized service for fast vehicle search and filtering.

Database: MongoDB (read-only cache)

Endpoints:

graph TB
    Client["🖥️ Client/User"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Filter Service"
        GetAll["<b>GET /api/filters</b><br/>Fetch all cars<br/>with filtering/search"]
        GetById["<b>GET /api/filters/{id}</b><br/>Fetch specific car<br/>by id"]

        FilterController["FilterController<br/>Handles 2 endpoints"]
        FilterSvc["🔍 FilterService<br/>Business Logic<br/>Read-Only Cache"]
    end

    subgraph "Database"
        MongoDB["🗄️ MongoDB<br/>filter_db<br/>Port: 27017"]
    end

    subgraph "Event Bus"
        Kafka["📨 Kafka<br/>Event Streaming<br/>Port: 9092"]
    end

    subgraph "Event Producers"
        InventorySvc["📦 Inventory Service<br/>Publishes car events"]
        MaintenanceSvc["🔧 Maintenance Service<br/>Publishes maintenance events"]
    end

    subgraph "Infrastructure"
        Keycloak["🔐 Keycloak<br/>Authentication<br/>Port: 8080"]
        Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
        Prometheus["📊 Prometheus<br/>Metrics<br/>Port: 9090"]
    end

%% Client to Gateway
    Client -->|HTTP Request| Gateway

%% Gateway to Controller
    Gateway -->|Route| FilterController

%% Controller to Endpoints
    FilterController -->|1. GET| GetAll
    FilterController -->|2. GET| GetById

%% Endpoints to Service
    GetAll -->|Process| FilterSvc
    GetById -->|Process| FilterSvc

%% Service to Database
    FilterSvc -->|Read Operations<br/>Only| MongoDB

%% Kafka Event Consumption
    Kafka -->|Consume Events<br/>car_created<br/>car_updated<br/>car_deleted<br/>car_availability_changed<br/>brand_created/updated/deleted<br/>model_created/updated/deleted<br/>car_maintenance_created<br/>car_returned| FilterSvc

%% Event Sources
    InventorySvc -->|Publish Events<br/>from Brands, Models, Cars| Kafka
    MaintenanceSvc -->|Publish Events<br/>Maintenance status changes| Kafka

%% Infrastructure Integrations
    FilterController -->|OAuth2/JWT| Keycloak
    FilterSvc -->|Send Traces| Zipkin
    FilterSvc -->|Expose Metrics| Prometheus

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style FilterController fill:#4A90E2,stroke:#3B73C4,color:#fff
    style FilterSvc fill:#4A90E2,stroke:#3B73C4,color:#fff
    style GetAll fill:#90EE90,stroke:#52B788,color:#000
    style GetById fill:#90EE90,stroke:#52B788,color:#000
    style MongoDB fill:#13AA52,stroke:#0E6D2F,color:#fff
    style Kafka fill:#FFE66D,stroke:#F1C40F,color:#000
    style InventorySvc fill:#27AE60,stroke:#1E8449,color:#fff
    style MaintenanceSvc fill:#FFB347,stroke:#E67E22,color:#fff
    style Keycloak fill:#95E1D3,stroke:#16A085,color:#000
    style Zipkin fill:#F38181,stroke:#E74C3C,color:#fff
    style Prometheus fill:#AA96DA,stroke:#8E44AD,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff

Loading

• GET /api/filters - Search all available cars with filters
• GET /api/filters/{id} - Fetch specific car details

Key Features:

• Optimized for read operations only
• Receives updates from Inventory & Maintenance via Kafka
• Provides fast search capability for users

---

7. Payment Service (Port: 8084)

Manages payment processing and transaction records for rental operations.

Database: PostgreSQL

Endpoints:

graph TB
    Client["🖥️ Client/User"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Payment Service"
        GetAll["<b>GET /api/payments</b><br/>Fetch all payments"]
        GetById["<b>GET /api/payments/{id}</b><br/>Fetch specific payment"]
        Create["<b>POST /api/payments</b><br/>Create payment record"]
        Update["<b>PUT /api/payments/{id}</b><br/>Update payment record"]
        Delete["<b>DELETE /api/payments/{id}</b><br/>Delete payment record"]
        ProcessPayment["<b>POST /api/payments/process-rental-payment</b><br/>Process rental payment<br/>Verify bank account balance"]

        PaymentController["PaymentController<br/>Handles 6 endpoints"]
        PaymentSvc["💳 PaymentService<br/>Business Logic<br/>Payment Processing"]
    end

    subgraph "Database"
        PostgreSQL["🗄️ PostgreSQL<br/>payment_db<br/>Port: 5432"]
    end

    subgraph "Service-to-Service Communication"
        RentalClient["Called by<br/>Rental Service<br/>@FeignClient<br/>POST /process-rental-payment"]
    end

    subgraph "Rental Service"
        RentalSvc["🚗 Rental Service<br/>Port: 8081<br/>Initiates payments"]
    end

    subgraph "Infrastructure"
        Keycloak["🔐 Keycloak<br/>Authentication<br/>Port: 8080"]
        Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
        Prometheus["📊 Prometheus<br/>Metrics<br/>Port: 9090"]
    end

%% Client to Gateway
    Client -->|HTTP Request| Gateway

%% Gateway to Controller
    Gateway -->|Route| PaymentController

%% Controller to Endpoints
    PaymentController -->|1. GET| GetAll
    PaymentController -->|2. GET| GetById
    PaymentController -->|3. POST| Create
    PaymentController -->|4. PUT| Update
    PaymentController -->|5. DELETE| Delete
    PaymentController -->|6. POST| ProcessPayment

%% Endpoints to Service
    GetAll -->|Process| PaymentSvc
    GetById -->|Process| PaymentSvc
    Create -->|Process| PaymentSvc
    Update -->|Process| PaymentSvc
    Delete -->|Process| PaymentSvc
    ProcessPayment -->|Process<br/>Verify balance<br/>Deduct amount| PaymentSvc

%% Service to Database
    PaymentSvc -->|CRUD Operations<br/>Record transactions| PostgreSQL

%% Feign Client Call
    RentalClient -->|Calls during checkout| ProcessPayment
    RentalSvc -->|REST/Feign| RentalClient

%% Infrastructure Integrations
    PaymentController -->|OAuth2/JWT| Keycloak
    PaymentSvc -->|Send Traces| Zipkin
    PaymentSvc -->|Expose Metrics| Prometheus

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style PaymentController fill:#8E44AD,stroke:#6C3483,color:#fff
    style PaymentSvc fill:#8E44AD,stroke:#6C3483,color:#fff
    style GetAll fill:#90EE90,stroke:#52B788,color:#000
    style GetById fill:#90EE90,stroke:#52B788,color:#000
    style Create fill:#87CEEB,stroke:#4A90E2,color:#000
    style Update fill:#F0E68C,stroke:#F39C12,color:#000
    style Delete fill:#FFB6C1,stroke:#E74C3C,color:#000
    style ProcessPayment fill:#DDA0DD,stroke:#9B59B6,color:#000
    style PostgreSQL fill:#336791,stroke:#0E4C92,color:#fff
    style RentalClient fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style RentalSvc fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style Keycloak fill:#95E1D3,stroke:#16A085,color:#000
    style Zipkin fill:#F38181,stroke:#E74C3C,color:#fff
    style Prometheus fill:#AA96DA,stroke:#8E44AD,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff

Loading

• GET /api/payments - Fetch all payment records
• GET /api/payments/{id} - Fetch specific payment
• POST /api/payments - Create payment record
• PUT /api/payments/{id} - Update payment record
• DELETE /api/payments/{id} - Delete payment record
• POST /api/payments/process-rental-payment - Process payment for rental (called by Rental Service)

Key Features:

• Verify bank account balances
• Process payments with balance deduction
• Record all payment transactions
• Used by Rental Service during checkout via Feign client

---

8. Invoice Service (Port: 8085)

Stores and retrieves rental transaction invoices.

Database: MongoDB

Endpoints:

graph TB
    Client["🖥️ Client/User"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Invoice Service"
        GetAll["<b>GET /api/invoices</b><br/>Fetch all invoices"]

        InvoiceController["InvoiceController<br/>Handles 1 endpoint"]
        InvoiceSvc["📄 InvoiceService<br/>Business Logic"]
    end

    subgraph "Database"
        MongoDB["🗄️ MongoDB<br/>invoice_db<br/>Port: 27018"]
    end

    subgraph "Event Bus"
        Kafka["📨 Kafka<br/>Event Streaming<br/>Port: 9092"]
    end

    subgraph "Event Producers"
        RentalSvc["🚗 Rental Service<br/>Publishes invoice events"]
    end

    subgraph "Infrastructure"
        Keycloak["🔐 Keycloak<br/>Authentication<br/>Port: 8080"]
        Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
        Prometheus["📊 Prometheus<br/>Metrics<br/>Port: 9090"]
    end

%% Client to Gateway
    Client -->|HTTP Request| Gateway

%% Gateway to Controller
    Gateway -->|Route| InvoiceController

%% Controller to Endpoint
    InvoiceController -->|1. GET| GetAll

%% Endpoint to Service
    GetAll -->|Process| InvoiceSvc

%% Service to Database
    InvoiceSvc -->|Read Operations| MongoDB

%% Kafka Event Consumption
    Kafka -->|Consume Events<br/>rental_invoice_created| InvoiceSvc

%% Event Source
    RentalSvc -->|Publish Events<br/>when rental completes| Kafka

%% Infrastructure Integrations
    InvoiceController -->|OAuth2/JWT| Keycloak
    InvoiceSvc -->|Send Traces| Zipkin
    InvoiceSvc -->|Expose Metrics| Prometheus

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style InvoiceController fill:#4A90E2,stroke:#3B73C4,color:#fff
    style InvoiceSvc fill:#4A90E2,stroke:#3B73C4,color:#fff
    style GetAll fill:#90EE90,stroke:#52B788,color:#000
    style MongoDB fill:#13AA52,stroke:#0E6D2F,color:#fff
    style Kafka fill:#FFE66D,stroke:#F1C40F,color:#000
    style RentalSvc fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style Keycloak fill:#95E1D3,stroke:#16A085,color:#000
    style Zipkin fill:#F38181,stroke:#E74C3C,color:#fff
    style Prometheus fill:#AA96DA,stroke:#8E44AD,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff

Loading

• GET /api/invoices - Fetch all invoices

Key Features:

• Read-only operations (no create/update/delete endpoints)
• Receives invoice data from Rental Service via Kafka
• Persists rental transaction records

---

9. Maintenance Service (Port: 8086)

Admin-facing service for managing vehicle maintenance operations.

Database: MySQL

Endpoints:

graph TB
    Client["🖥️ Client/Admin"]

    subgraph "API Gateway"
        Gateway["🔗 Spring Cloud Gateway<br/>Port: 9010"]
    end

    subgraph "Maintenance Service"
        GetAll["<b>GET /api/maintenances</b><br/>Fetch all maintenance records"]
        GetById["<b>GET /api/maintenances/{id}</b><br/>Fetch specific maintenance record"]
        Create["<b>POST /api/maintenances</b><br/>Create new maintenance request"]
        Return["<b>PUT /api/maintenances/return</b><br/>Return car from maintenance"]
        Update["<b>PUT /api/maintenances/{id}</b><br/>Update maintenance record"]
        Delete["<b>DELETE /api/maintenances/{id}</b><br/>Delete maintenance record"]

        MaintenanceSvc["🔧 MaintenanceService<br/>Business Logic"]
        MaintenanceController["MaintenanceController<br/>Handles 6 endpoints"]
    end

    subgraph "Database"
        MySQL["🗄️ MySQL<br/>maintenance_db<br/>Port: 3307"]
    end

    subgraph "Service-to-Service Communication"
        CarClient["CarClient<br/>@FeignClient"]
        CheckAvail["<b>GET /api/cars/check-car-available/{carId}</b><br/>Verify car availability"]
    end

    subgraph "Inventory Service"
        InventorySvc["📦 Inventory Service<br/>Port: 8082"]
    end

    subgraph "Event Bus"
        Kafka["📨 Kafka<br/>Event Streaming<br/>Port: 9092"]
    end

    subgraph "Dependent Services"
        FilterSvc["🔍 Filter Service<br/>Updates car status"]
        InventoryEvent["📦 Inventory Service<br/>Updates car availability"]
    end

    subgraph "Infrastructure"
        Keycloak["🔐 Keycloak<br/>Authentication<br/>Port: 8080"]
        Zipkin["🔍 Zipkin<br/>Distributed Tracing<br/>Port: 9411"]
        Prometheus["📊 Prometheus<br/>Metrics<br/>Port: 9090"]
    end

%% Client to Gateway
    Client -->|HTTP Request| Gateway

%% Gateway to Endpoints
    Gateway -->|Route| MaintenanceController

%% Endpoints to Service
    MaintenanceController -->|1. GET| GetAll
    MaintenanceController -->|2. GET| GetById
    MaintenanceController -->|3. POST| Create
    MaintenanceController -->|4. PUT| Return
    MaintenanceController -->|5. PUT| Update
    MaintenanceController -->|6. DELETE| Delete

%% Endpoints to Business Logic
    GetAll -->|Process| MaintenanceSvc
    GetById -->|Process| MaintenanceSvc
    Create -->|Process| MaintenanceSvc
    Return -->|Process| MaintenanceSvc
    Update -->|Process| MaintenanceSvc
    Delete -->|Process| MaintenanceSvc

%% Business Logic to Database
    MaintenanceSvc -->|CRUD Operations| MySQL

%% Feign Client Call (internal REST)
    MaintenanceSvc -->|REST/Feign| CarClient
    CarClient -->|Check availability| CheckAvail
    CheckAvail -->|GET call| InventorySvc

%% Kafka Events
    MaintenanceSvc -->|Publish Events<br/>car_maintenance_created<br/>car_returned| Kafka

%% Event Consumers
    Kafka -->|Consume| FilterSvc
    Kafka -->|Consume| InventoryEvent

%% Infrastructure Integrations
    MaintenanceController -->|OAuth2/JWT| Keycloak
    MaintenanceSvc -->|Send Traces| Zipkin
    MaintenanceSvc -->|Expose Metrics| Prometheus

%% Styling
    style Gateway fill:#FF6B6B,stroke:#C92A2A,color:#fff
    style MaintenanceController fill:#FFB347,stroke:#E67E22,color:#fff
    style MaintenanceSvc fill:#FFB347,stroke:#E67E22,color:#fff
    style GetAll fill:#90EE90,stroke:#52B788,color:#000
    style GetById fill:#90EE90,stroke:#52B788,color:#000
    style Create fill:#87CEEB,stroke:#4A90E2,color:#000
    style Return fill:#DDA0DD,stroke:#9B59B6,color:#000
    style Update fill:#F0E68C,stroke:#F39C12,color:#000
    style Delete fill:#FFB6C1,stroke:#E74C3C,color:#000
    style MySQL fill:#336791,stroke:#0E4C92,color:#fff
    style CheckAvail fill:#FFA500,stroke:#D97706,color:#000
    style CarClient fill:#FF6B00,stroke:#CC5500,color:#fff
    style Kafka fill:#FFE66D,stroke:#F1C40F,color:#000
    style FilterSvc fill:#27AE60,stroke:#1E8449,color:#fff
    style InventoryEvent fill:#F39C12,stroke:#D68910,color:#fff
    style Keycloak fill:#95E1D3,stroke:#16A085,color:#000
    style Zipkin fill:#F38181,stroke:#E74C3C,color:#fff
    style Prometheus fill:#AA96DA,stroke:#8E44AD,color:#fff
    style Client fill:#2C3E50,stroke:#1A252F,color:#fff

Loading

• GET /api/maintenances - Fetch all maintenance records
• GET /api/maintenances/{id} - Fetch specific maintenance
• POST /api/maintenances - Create maintenance request
• PUT /api/maintenances/{id} - Update maintenance record
• PUT /api/maintenances/return - Return car from maintenance
• DELETE /api/maintenances/{id} - Delete maintenance record

Key Features:

• Send cars for maintenance
• Track maintenance status
• Verify car availability via Inventory Service (Feign)
• Publish maintenance events to Kafka for Inventory & Filter updates

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API Endpoints

Summary

Service	Count	Type
Rental	5	CRUD + Transaction
Inventory - Brands	5	CRUD
Inventory - Models	5	CRUD
Inventory - Cars	7	CRUD + Special
Filter	2	Read-only
Payment	6	CRUD + Processing
Invoice	1	Read-only
Maintenance	6	CRUD + Special
Total	45

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Layered Architecture

Each microservice follows a clean layered architecture with clear separation of concerns:

Data Layer (entities & repositories)

• Entities: JPA annotated POJO classes with relationships
• Repositories: JPA repository interfaces with custom query methods
• First Code approach applied (domain model first)

Business Layer (business logic)

Abstracts (Interfaces)

• Service interfaces defining contracts
• Enable future technology integration
• Support SOLID principles (Liskov, Interface Segregation, Dependency Inversion)

Concretes (Implementations)

• Implement service interfaces
• Apply business rules and validation
• Orchestrate Feign REST calls
• Dispatch Kafka events
• Return DTOs (via ModelMapper)

Rules (Business Rules & Validation)

• Custom exception throwing for error scenarios
• Business logic validation before operations
• Improves code readability and error handling
• Prevents database errors with pre-checks

API Layer (REST endpoints & clients)

Controllers

• REST endpoint definitions
• Dependency injection of business services
• Request/response handling

Clients (Feign)

• OpenFeign declarative REST clients for inter-service calls
• Resilience4j Retry pattern for fault tolerance
• Fallback error handling with custom exceptions
• Logging via SLF4J

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Communication Patterns

Synchronous Communication (REST)

Feign Clients with Retry Pattern:

Used for critical operations requiring immediate response:

• Rental → Inventory (Resilience4j Retry)

  • Check car availability before rental
  • Get car details for invoice

• Rental → Payment (Resilience4j Retry)

  • Process payment during checkout

• Maintenance → Inventory

  • Verify car availability before maintenance

Why Retry Pattern?

• Handles transient failures (service temporarily unavailable)
• Configurable retry attempts and intervals
• Prevents cascading failures

Asynchronous Communication (Kafka)

Event-Driven Architecture:

Used for eventual consistency and decoupled updates:

Event Flows:

1. Rental Events

   • rental_created → Inventory & Filter Services
   • rental_completed → Inventory & Filter Services
   • rental_invoice_created → Invoice Service

2. Inventory Events

   • brand_created/updated/deleted → Filter Service
   • model_created/updated/deleted → Filter Service
   • car_created/updated/deleted → Filter Service
   • car_availability_changed → Filter Service

3. Maintenance Events

   • car_maintenance_created → Inventory & Filter Services
   • car_returned → Inventory & Filter Services

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Key Design Patterns

Architectural Patterns

• Microservices - Decomposed by business capability
• API Gateway - Single entry point
• Service Discovery - Eureka registry
• Config Server - Centralized configuration
• Event-Driven Architecture - Kafka for async communication

Resilience Patterns

• Retry Pattern - Resilience4j for transient failures
• Circuit Breaker - Prevent cascading failures
• Fallback - Error handling for service failures

Design Principles

• SOLID Principles

  • Single Responsibility: Each class has one reason to change
  • Open/Closed: Open for extension, closed for modification
  • Liskov Substitution: Interfaces enable interchangeable implementations
  • Interface Segregation: Specific interfaces for specific needs
  • Dependency Inversion: Depend on abstractions, not concrete classes

• GRASP Principles

  • Creator: Spring manages object creation
  • Controller: Service layer controls business logic
  • High Cohesion: Related responsibilities grouped
  • Low Coupling: Services communicate via interfaces

Data Patterns

• Repository Pattern - Abstract data access
• DTO Pattern - Request/Response objects via ModelMapper
• Database Per Service - Microservice data isolation
• Eventual Consistency - Async updates via Kafka

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Setup & Deployment

Prerequisites

• Java 17+
• Maven 3.8+
• Docker & Docker Compose
• Git

Running the System

1. Start Infrastructure (Docker Compose)

   docker-compose up -d

   This starts:

   • Kafka (Port: 9092)
   • PostgreSQL instances
   • MySQL instance
   • MongoDB instances
   • Keycloak (Port: 8080)
   • Zipkin (Port: 9411)
   • Prometheus (Port: 9090)
   • Grafana (Port: 3000)

2. Start Microservices

   # Discovery Server
   cd discovery-server && mvn spring-boot:run
   
   # Config Server
   cd config-server && mvn spring-boot:run
   
   # API Gateway
   cd api-gateway && mvn spring-boot:run
   
   # All other services (in any order)
   cd rental-service && mvn spring-boot:run
   cd inventory-service && mvn spring-boot:run
   cd filter-service && mvn spring-boot:run
   cd payment-service && mvn spring-boot:run
   cd invoice-service && mvn spring-boot:run
   cd maintenance-service && mvn spring-boot:run

Accessing Services

• API Gateway: http://localhost:9010
• Eureka Dashboard: http://localhost:8761
• Keycloak: http://localhost:8080
• Zipkin: http://localhost:9411
• Prometheus: http://localhost:9090
• Grafana: http://localhost:3000

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Key Features & Highlights

✅ Enterprise Architecture

• Microservices with clear boundaries
• Distributed systems patterns
• Scalable & maintainable codebase

✅ Clean Code

• SOLID principles throughout
• GRASP patterns applied
• Layered architecture per service

✅ Resilience

• Retry pattern for transient failures
• Fallback mechanisms
• Circuit breaker ready

✅ Observability

• Distributed tracing (Zipkin)
• Metrics collection (Prometheus)
• Visualization (Grafana)
• Structured logging (SLF4J)

✅ Security

• OAuth2/OIDC via Keycloak
• JWT token validation

✅ Data Consistency

• Strong consistency for critical operations (REST)
• Eventual consistency for updates (Kafka)

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Future Enhancements

• API rate limiting & throttling
• Advanced search filters
• Real-time notifications
• Advanced payment methods integration
• Vehicle tracking/GPS integration
• Machine learning for pricing optimization
• Mobile application
• Advanced analytics dashboard

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Project Statistics

• Total Endpoints: 45
• Microservices: 6
• Infrastructure Services: 3
• Databases: 3 (PostgreSQL, MySQL, MongoDB)
• Event Topics: 8+
• Technology Stack: 15+ frameworks/libraries

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Authors & Contribution

This project demonstrates enterprise-grade microservices architecture with emphasis on:

• Clean code and SOLID principles
• Distributed systems design
• Production-ready resilience patterns
• Comprehensive observability

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