ADR-0002: Use a Microservices Architecture

• Status: Accepted
• Date: 2025-09-11
• Authors: Senior Systems Analyst

Context and Problem Statement

The project requires a scalable and maintainable architecture that can evolve over time. We need to support independent development cycles for different domains of functionality (e.g., authentication, reporting, core business logic) and ensure that a failure in one part of the system does not cascade and bring down the entire application.

Considered Options

• Option 1: Monolithic Architecture

  • Description: Build a single, unified application containing all business logic for the frontend, API gateway, and authentication service.
  • Pros:
    • Simpler initial setup and development.
    • Easier to test end-to-end.
    • Single codebase is easier to manage for a small team.
  • Cons:
    • Becomes difficult to scale and maintain as the application grows.
    • A single bug can bring down the entire application.
    • Technology stack is locked in.
    • Independent team development and deployment is impossible.

• Option 2: Microservices Architecture (Chosen)

  • Description: Decompose the application into small, independent services, each responsible for a specific business domain. In our case, this starts with the AuthService, ApiGateway, and Frontend as separate, deployable units.
  • Pros:
    • Scalability: Each service can be scaled independently based on its specific load.
    • Resilience: A failure in one service (e.g., a reporting service) does not necessarily impact critical services like authentication.
    • Team Autonomy: Enables different teams to develop, deploy, and maintain their services independently.
    • Technological Flexibility: Each service could, in theory, use a different technology stack.
  • Cons:
    • Increased Complexity: Requires managing inter-service communication, service discovery, and distributed data.
    • Operational Overhead: More services to deploy, monitor, and manage.
    • Testing Challenges: End-to-end testing becomes more complex.

Decision

We will adopt a Microservices Architecture. The initial decomposition into a separate Frontend, ApiGateway, and AuthService provides a clear and logical separation of concerns that aligns with our goals for scalability and team autonomy.

Consequences

Positive

• The AuthService can be scaled and secured independently of other application components.
• The clear separation of concerns simplifies the codebase for each individual service.
• This model provides a clear pattern for adding new business domains (e.g., a future ReportingService) without disrupting existing ones.

Negative

• We must invest in robust inter-service communication protocols (addressed in ADR-0003).
• We accept the increased operational overhead for deployment and monitoring, which will be managed via containerization and orchestration.