Project Assumptions

A microservices-based architecture following principles:

• Domain-Driven Design.
• Event-Driven Architecture.
• Hexagonal Architecture.
• Separation of Concerns.
• Choreography pattern for service coordination.
• Saga pattern for distributed transactions.
• Outbox pattern for reliable event publishing.
• SOLID.

Architecture Graph

Technology Stack

• Back-end: Spring Boot, Kotlin, Gradle Kotlin DSL (a separate build for each service).
• Database: PostgreSQL (a separate instance for each service).
• Message Broker: Apache Kafka KRaft (Zookeeper-less).
• Identity Provider: Keycloak (OAuth2 / OpenID Connect).
• API Documentation: OpenAPI (Swagger).
• Containerization: Docker / Podman.
• Authentication: Keycloak JWT + refresh tokens (HttpOnly secure cookie via BFF pattern).
• Testing: JUnit, Testcontainers.
• Static Analysis: ktlint, Detekt.
• Documentation: Dokka for code docs.
• Infrastructure as Code: Terraform for Kafka topic provisioning.
• Build and Dependency Management: Gradle with composite builds for modularization.
• Schema Management: Apache Avro with Schema Registry for versioning and compatibility.

Documentation

• Architecture — components and design principles.
• Saga Pattern & Transactional Outbox — saga engine, outbox, idempotent receiver.
• Concurrency Control — optimistic locking, ETags, saga and outbox concurrency.
• Keycloak Configuration — realm setup, authentication flow, role management.
• Development Setup — prerequisites, getting started, service URLs, API testing, code style.