Decision Logs

The biggest problem in software architecture isn't making the wrong decision; it's forgetting why you made it.

Without written records, teams re-litigate the same arguments every 6 months. We solve this using RFCs (process) and ADRs (artifacts).

ADRs (Architectural Decision Records)

An ADR is a short text file that captures a significant architectural decision, along with its context and consequences.

The Lifecycle

An ADR is immutable once finalized. If you change your mind later, you create a new ADR that supersedes the old one.

RFC vs. ADR

People confuse these. They are two sides of the same coin.

1. The RFC (Request For Comments): This is the Active Discussion. It is a document (often a Google Doc or a PR) where people comment, argue, and suggest changes.
2. The ADR (Record): This is the Snapshot. Once the RFC discussion settles and a decision is made, you summarize the outcome into a frozen ADR file committed to the repo.

The MADR Template

Markdown Architectural Decision Record. This is the industry standard format (Michael Nygard style).

Example: ADR 001- Database Technology Selection

Status: Accepted
Date: 2023-06-15
Deciders: Architecture Team (Alice and Bob)

Context and Problem Statement

Our e-commerce platform is experiencing rapid growth, and our current MongoDB setup is struggling with transaction consistency and complex reporting requirements. We need a database solution that can handle ACID transactions for orders while supporting high-traffic product catalog queries.

Decision Drivers

• Transaction consistency for financial operations
• Performance for read-heavy product catalog
• Team expertise and hiring considerations
• Operational complexity and maintenance overhead
• Cost optimization for scaling

Considered Options

1. PostgreSQL - Traditional relational database
2. MongoDB (Current) - Document database
3. Hybrid Approach - PostgreSQL for transactions, MongoDB for catalog

Decision Outcome

Chosen option: Option 3 (Hybrid Approach)

Positive Consequences

• Best of both worlds: ACID transactions where needed, document flexibility elsewhere
• Team can leverage existing MongoDB expertise
• Gradual migration path reduces risk
• Optimized for different access patterns

Negative Consequences

• Increased operational complexity
• Data synchronization challenges
• Higher infrastructure costs
• Need for polyglot persistence skills

Example: ADR 002- Authentication Strategy

Status: Accepted
Date: 2023-08-22
Deciders: Security Team (Alice and Bob)

Context and Problem Statement

Our current authentication system uses custom JWT implementation with multiple auth providers (Google, Facebook, email). This has led to security vulnerabilities, maintenance overhead, and difficulty adding new providers.

Decision Drivers

• Security compliance requirements
• Developer productivity
• User experience improvements
• Maintenance burden reduction
• Future extensibility

Considered Options

1. Continue Custom Implementation - Maintain current system
2. Auth0 Implementation - Third-party authentication service
3. Keycloak Open Source - Self-hosted identity provider
4. AWS Cognito - Cloud-native identity service

Decision Outcome

Chosen option: Option 2 (Auth0 Implementation)

Positive Consequences

• Enterprise-grade security features
• Reduced development time for auth features
• Built-in social login providers
• Comprehensive audit and compliance tools
• 24/7 security monitoring

Negative Consequences

• Additional monthly cost (~$3,000/month)
• Vendor dependency
• Potential data privacy concerns
• Migration complexity

Best Practices for RFCs & ADRs

Writing Good ADRs

Be Specific:

• Include exact technologies, versions, and configurations
• Quantify benefits and costs where possible
• Reference specific requirements or constraints

Include Context:

• What business problem are we solving?
• What constraints influenced the decision?
• What were the timeline and resource limitations?

Consider Alternatives:

• Document why other options were rejected
• Include trade-offs for each option
• Acknowledge when decision was close call

Managing the Process

RFC Workflow:

1. Proposal: Create draft RFC in collaborative document
2. Review: Share with stakeholders for feedback period (5-10 days)
3. Discussion: Schedule RFC review meeting with key decision makers
4. Decision: Approve, reject, or request changes
5. Documentation: Convert approved RFC to ADR in repository
6. Implementation: Begin work with clear requirements

ADR Organization:

docs/architecture/adr/
├── 001-database-selection.md
├── 002-authentication-strategy.md
├── 003-api-gateway-choice.md
├── 004-monitoring-platform.md
├── 005-deprecated-database-selection.md
└── README.md  # Index of all ADRs

Integration with Development

Link to Code:

• Reference ADR numbers in commit messages
• Link ADRs from relevant code directories
• Include ADR status in architecture diagrams
• Tag releases with major ADR implementations

Review Process:

• Review ADRs annually for continued relevance
• Update deprecated status when superseded
• Consider ADR impacts during code reviews
• Include ADR compliance in architectural reviews

Tools and Automation

ADR Management Tools

Simple Approach:

• Markdown files in git repository
• Manual numbering and organization
• Template-based creation process

Advanced Tools:

• ADR Tools: Automated ADR generation and management
• MADR-Tools: Enhanced Markdown ADR workflow
• Confluence/Notion: Integrated documentation platforms

Automation Ideas

Validation Scripts:

• Check ADR format compliance
• Validate required sections are present
• Ensure consistent numbering
• Generate index automatically

Integration Hooks:

• Git hooks to prompt for ADR on significant changes
• CI/CD pipeline to check ADR references
• Automated documentation updates
• Slack notifications for new ADRs