Crosscutting concerns

Use this template to describe the concerns that cut across every part of a system, such as security, logging, error handling and configuration. Writing them down once stops each component solving them differently.

Template

---
title: Crosscutting Concerns / Architectural Concerns - [System/Product Name]
status: Draft / Reviewed / Approved / Baselined / Evolving
date: YYYY-MM-DD
author: [Name or Role of Lead Architect]
version: 1.0
related_documents:
  - Architecture Vision - [System/Product Name]
  - Architecture Principles - [System/Product Name]
---

# Crosscutting Concerns / Architectural Concerns: [System/Product Name]

This document defines the strategies and approaches for addressing key crosscutting concerns within the [System/Product Name]'s architecture. These concerns impact multiple parts of the system and require a consistent, overarching strategy to ensure coherence, quality, and maintainability.

---

## 1. Introduction

### 1.1 Purpose

The purpose of this document is to:
* Identify and define the common architectural concerns that span multiple components or subsystems.
* Document the chosen strategy and approach for addressing each concern.
* Ensure consistency in implementation across the architecture.
* Provide guidance for developers and architects on how to handle these concerns.
* Facilitate understanding and communication of complex architectural aspects.

### 1.2 Scope

This document covers the high-level strategy and common implementation patterns for crosscutting concerns across the [System/Product Name]. It does not delve into component-specific implementation details, which will be covered in detailed design specifications (SDS).

### 1.3 Definitions and Acronyms

[List any relevant terms, definitions, or acronyms.]

## 2. Crosscutting Concerns Log

This log provides a summary of each identified crosscutting concern.

| Concern ID | Concern Name | Description (Brief) | Strategy (Brief) | Owner | Last Updated |
|------------|--------------|---------------------|------------------|-------|--------------|
| **CC-001** | Security     | Protecting system from unauthorized access. | Layered security, least privilege, encryption. | Jane Doe | YYYY-MM-DD   |
| **CC-002** | Logging & Monitoring | Capturing and analyzing system events and metrics. | Centralized logging, distributed tracing. | John Smith | YYYY-MM-DD   |
| **CC-003** | Error Handling & Resilience | Graceful degradation and recovery from failures. | Circuit breakers, retries, consistent error responses. | Alice Brown | YYYY-MM-DD   |
| **CC-004** | Configuration Management | Managing application settings and environment variables. | Externalized, version-controlled configuration. | Bob White | YYYY-MM-DD   |
| **CC-005** | Authentication | Verifying user/system identity. | OAuth 2.0, JWT. | Carol Green | YYYY-MM-DD   |
| **CC-006** | Authorization  | Controlling access to resources. | Role-Based Access Control (RBAC). | Carol Green | YYYY-MM-DD   |

## 3. Detailed Crosscutting Concerns

For each crosscutting concern, provide a detailed description of the strategy, chosen solution, implications, and implementation guidelines.

### 3.1 Concern: Security (CC-001)

#### 3.1.1 Description

[Briefly describe what "security" means in the context of this system (e.g., protecting data at rest and in transit, preventing unauthorized access, ensuring data integrity).]

#### 3.1.2 Architectural Strategy / Solution

[Describe the high-level strategy for addressing security. e.g., "Implement a layered security approach with defense-in-depth principles. Utilize industry-standard encryption protocols. Adopt a 'least privilege' model for all access."]

* **Key Technologies/Patterns:** [e.g., TLS, OAuth 2.0, JWT, HSMs, Web Application Firewalls (WAFs).]
* **Related ADRs:** [Link to relevant ADRs, e.g., ADR-005: "Choice of Authentication Protocol."]

#### 3.1.3 Implications

* **Benefits:** [e.g., "Reduced risk of data breaches," "Compliance with regulatory requirements," "Increased customer trust."]
* **Drawbacks/Trade-offs:** [e.g., "Increased complexity in initial setup," "Potential performance overhead due to encryption."]

#### 3.1.4 Implementation Guidelines

[Provide high-level guidelines for how this concern should be implemented across components.]

* **Data Protection:** All sensitive data must be encrypted at rest (AES-256) and in transit (TLS 1.2+).
* **Access Control:** Implement Role-Based Access Control (RBAC) for all internal and external APIs.
* **Input Validation:** All external inputs must be validated at the service boundary.
* **Vulnerability Management:** Regular security scans and penetration testing are mandatory.

### 3.2 Concern: Logging & Monitoring (CC-002)

#### 3.2.1 Description

[Briefly describe the purpose of logging and monitoring in this system (e.g., for debugging, auditing, performance tracking, operational visibility).]

#### 3.2.2 Architectural Strategy / Solution

[Describe the strategy. e.g., "Implement centralized logging and distributed tracing. Standardize log formats and levels. Utilize metrics for real-time operational visibility."]

* **Key Technologies/Patterns:** [e.g., ELK Stack (Elasticsearch, Logstash, Kibana), Prometheus, Grafana, OpenTelemetry.]
* **Related ADRs:** [e.g., ADR-010: "Centralized Logging Solution Selection."]

#### 3.2.3 Implications

* **Benefits:** [e.g., "Faster incident resolution," "Improved system observability," "Better understanding of user behavior."]
* **Drawbacks/Trade-offs:** [e.g., "Storage costs for logs," "Performance overhead if logging is excessive."]

#### 3.2.4 Implementation Guidelines

* **Standardized Logging:** Use a common logging library and predefined log levels (DEBUG, INFO, WARN, ERROR, FATAL).
* **Contextual Logging:** Include relevant context (e.g., request ID, user ID, component name) in all logs.
* **Distributed Tracing:** Instrument services to support end-to-end tracing of requests.
* **Key Metrics:** Define and collect essential metrics for each service (e.g., request rates, error rates, latency).

### 3.3 Concern: Error Handling & Resilience (CC-003)

#### 3.3.1 Description

[Describe the approach to handling errors and ensuring the system can withstand and recover from failures.]

#### 3.3.2 Architectural Strategy / Solution

[e.g., "Implement consistent error response formats. Utilize resilience patterns like circuit breakers, retries, and bulkheads. Design for graceful degradation."]

* **Key Technologies/Patterns:** [e.g., Hystrix (or similar), Polly, consistent API error schemas.]
* **Related ADRs:** [e.g., ADR-015: "API Error Response Standard."]

#### 3.3.3 Implications

* **Benefits:** [e.g., "Improved system stability and availability," "Better user experience during partial failures," "Faster recovery from outages."]
* **Drawbacks/Trade-offs:** [e.g., "Increased complexity in service interactions," "Requires careful testing of failure scenarios."]

#### 3.3.4 Implementation Guidelines

* **Consistent Error Responses:** All APIs/interfaces must return errors in a standardized format.
* **Circuit Breakers:** Implement circuit breakers for calls to external services or unreliable internal components.
* **Retries:** Use exponential backoff and jitter for transient error retries.
* **Idempotency:** Design operations to be idempotent where possible.

### 3.4 Concern: Configuration Management (CC-004)

#### 3.4.1 Description

[How are application and system configurations managed across different environments?]

#### 3.4.2 Architectural Strategy / Solution

[e.g., "Externalize all environment-specific and sensitive configurations. Version control configuration files. Use a secure configuration store for secrets."]

* **Key Technologies/Patterns:** [e.g., Environment variables, Kubernetes ConfigMaps/Secrets, HashiCorp Vault, AWS Secrets Manager, Azure Key Vault.]
* **Related ADRs:** [e.g., ADR-020: "Secure Configuration Management Solution."]

#### 3.4.3 Implications

* **Benefits:** [e.g., "Easier environment promotion," "Reduced risk of configuration errors," "Improved security for sensitive data."]
* **Drawbacks/Trade-offs:** [e.g., "Initial setup overhead," "Requires careful access control to configuration stores."]

#### 3.4.4 Implementation Guidelines

* **Externalize Config:** No hardcoded configurations in code.
* **Environment Variables:** Use environment variables for non-sensitive, environment-specific settings.
* **Secret Management:** Store all sensitive data (API keys, database credentials) in a dedicated, secure secret management system.
* **Version Control:** Configuration files (excluding secrets) should be version-controlled.

### 3.5 Concern: Authentication (CC-005)

#### 3.5.1 Description

[How users and other systems prove their identity to the system.]

#### 3.5.2 Architectural Strategy / Solution

[e.g., "Implement a centralized authentication service. Use industry-standard protocols for user authentication and authorization."]

* **Key Technologies/Patterns:** [e.g., OAuth 2.0, OpenID Connect, JWT (JSON Web Tokens), Identity Providers (Okta, Auth0, Azure AD).]
* **Related ADRs:** [e.g., ADR-025: "Centralized Identity Management System."]

#### 3.5.3 Implications

* **Benefits:** [e.g., "Single Sign-On (SSO) for users," "Consistent security posture," "Reduced development effort for authentication."]
* **Drawbacks/Trade-offs:** [e.g., "Complexity of protocol implementation," "Reliance on external identity provider."]

#### 3.5.4 Implementation Guidelines

* **Centralized Auth:** All authentication requests must go through the designated authentication service.
* **Token-Based Auth:** Use JWTs for stateless authentication between services.
* **Secure Storage:** Store user credentials securely (e.g., hashed and salted passwords).

### 3.6 Concern: Authorization (CC-006)

#### 3.6.1 Description

[How the system determines what authenticated users/systems are allowed to do.]

#### 3.6.2 Architectural Strategy / Solution

[e.g., "Implement Role-Based Access Control (RBAC) or Attribute-Based Access Control (ABAC)."]

* **Key Technologies/Patterns:** [e.g., RBAC frameworks, policy engines.]
* **Related ADRs:** [e.g., ADR-030: "Authorization Model Selection."]

#### 3.6.3 Implications

* **Benefits:** [e.g., "Granular control over resources," "Easier management of user permissions."]
* **Drawbacks/Trade-offs:** [e.g., "Complexity in defining roles/policies," "Performance overhead for complex evaluations."]

#### 3.6.4 Implementation Guidelines

* **Policy Enforcement:** Enforce authorization policies at the service/API boundary.
* **Role/Permission Definition:** Clearly define roles and their associated permissions.
* **Auditing:** Log all authorization attempts and failures.

## 4. Application and Maintenance

### 4.1 Application Guidelines

* These concerns should be considered during all design phases (from high-level architecture to detailed component design).
* All new components and features must adhere to the defined strategies for these concerns.
* Any deviations must be explicitly justified and documented, ideally via an ADR.

### 4.2 Maintenance and Evolution

* This document is a living artifact and should be reviewed periodically (e.g., annually or as part of major architectural shifts).
* New crosscutting concerns may emerge and should be added as needed.
* Strategies may evolve based on new technologies, threats, or business needs.

## 5. References

[List any other relevant documents (e.g., Architecture Vision, Architecture Principles, specific ADRs, security policies, coding standards) referenced in this document.]