Architecture Decision Records (ADR) Templates
Templates for documenting architectural decisions throughout the GISE methodology. Architecture Decision Records help teams understand the rationale behind technical choices and their long-term implications.
ADR Template Structure
Basic ADR Template
# ADR-[NUMBER]: [DECISION TITLE]
**Status**: [Proposed | Accepted | Rejected | Deprecated | Superseded]
**Date**: [YYYY-MM-DD]
**Authors**: [Decision makers]
**Reviewers**: [Technical reviewers]
## Context
[Describe the situation and problem statement that motivates this decision]
### Background
- Current state of the system
- Constraints and requirements
- Stakeholders involved
### Problem Statement
Clear description of the architectural challenge or choice that needs to be made.
## Considered Options
### Option 1: [Option Name]
**Description**: [Brief description of this option]
**Pros**:
- [Advantage 1]
- [Advantage 2]
- [Advantage 3]
**Cons**:
- [Disadvantage 1]
- [Disadvantage 2]
- [Disadvantage 3]
**Estimated Effort**: [Time/complexity estimate]
**Risk Level**: [High/Medium/Low]
### Option 2: [Option Name]
[Same structure as Option 1]
### Option 3: [Option Name]
[Same structure as Option 1]
## Decision
**Chosen Option**: [Selected option with rationale]
### Rationale
[Explain why this option was selected over others]
### Implementation Details
- [Key implementation considerations]
- [Technology choices]
- [Integration points]
### Success Metrics
- [How will we measure success of this decision]
- [Performance targets]
- [Quality metrics]
## Consequences
### Positive
- [Expected benefits]
- [Solved problems]
- [Improved capabilities]
### Negative
- [Trade-offs made]
- [New limitations introduced]
- [Technical debt created]
### Neutral
- [Other impacts to consider]
## Follow-up Actions
- [ ] [Action item 1 with owner and timeline]
- [ ] [Action item 2 with owner and timeline]
- [ ] [Review date for this decision]
## References
- [Related ADRs]
- [Technical documentation]
- [External resources]
Common ADR Templates
Database Technology Choice
# ADR-001: Database Technology Selection
**Status**: Accepted
**Date**: 2024-01-15
**Authors**: Tech Lead, Senior Developer
**Reviewers**: Architecture Team
## Context
We need to select a primary database technology for our new customer management system. The system will handle user accounts, product catalogs, order processing, and reporting.
### Requirements
- Handle 10,000+ concurrent users
- ACID compliance for financial transactions
- Complex relational queries for reporting
- Horizontal scaling capability
- Strong consistency for critical data
## Considered Options
### Option 1: PostgreSQL
**Description**: Open-source relational database with strong ACID compliance
**Pros**:
- Excellent ACID compliance
- Rich SQL feature set with advanced queries
- Strong community and ecosystem
- JSON support for flexible schemas
- Proven scalability patterns
**Cons**:
- Requires more database administration expertise
- Horizontal scaling requires additional tools (Citus, sharding)
- Higher resource usage than simpler databases
**Estimated Effort**: 2-3 weeks setup and configuration
**Risk Level**: Low
### Option 2: MongoDB
**Description**: NoSQL document database with flexible schema
**Pros**:
- Flexible schema design
- Built-in horizontal scaling
- Excellent developer experience
- Strong performance for read-heavy workloads
**Cons**:
- Limited ACID transactions (only within single documents)
- Learning curve for SQL-experienced team
- Complex queries can be challenging
- Potential data consistency issues
**Estimated Effort**: 3-4 weeks learning curve
**Risk Level**: Medium
## Decision
**Chosen Option**: PostgreSQL
### Rationale
PostgreSQL was selected because:
1. ACID compliance is critical for financial transactions
2. Team has strong SQL expertise
3. Complex reporting requirements favor relational model
4. Strong ecosystem support and documentation
5. Proven track record in similar applications
### Implementation Details
- Use PostgreSQL 15+ with connection pooling (PgBouncer)
- Implement read replicas for reporting workloads
- Use JSON columns for flexible metadata storage
- Plan for horizontal scaling with Citus if needed
## Consequences
### Positive
- Strong data consistency guarantees
- Leverages existing team SQL expertise
- Excellent tooling and monitoring options
- Clear migration path from existing systems
### Negative
- More complex horizontal scaling story
- Requires dedicated database administration
- Higher infrastructure costs than simpler solutions
## Follow-up Actions
- [ ] Setup development PostgreSQL environment (DevOps, Week 1)
- [ ] Create database schema migration strategy (Backend Team, Week 2)
- [ ] Establish backup and recovery procedures (DevOps, Week 3)
- [ ] Performance testing with realistic data volumes (QA Team, Week 4)
Authentication Architecture
# ADR-002: Authentication & Authorization Architecture
**Status**: Accepted
**Date**: 2024-01-20
**Authors**: Security Architect, Tech Lead
**Reviewers**: Security Team, Development Team
## Context
Design authentication and authorization system for multi-tenant SaaS application with web and mobile clients.
### Requirements
- Support for multiple client types (web, mobile, API)
- Multi-tenant user isolation
- Role-based access control (RBAC)
- Integration with existing identity providers
- Scalable to 50,000+ users
- Security compliance (SOC 2, GDPR)
## Considered Options
### Option 1: JWT with Custom Auth Service
**Description**: Build custom authentication service issuing JWT tokens
**Pros**:
- Full control over authentication logic
- Custom claims for tenant and role information
- Stateless architecture
- Good performance
**Cons**:
- High development and maintenance overhead
- Security expertise required
- Token revocation complexity
- Audit and compliance burden
### Option 2: OAuth 2.0 with Auth0
**Description**: Use Auth0 as managed authentication provider
**Pros**:
- Production-ready security features
- Built-in compliance and auditing
- Multiple authentication methods
- Extensive documentation and SDKs
**Cons**:
- Vendor lock-in
- Monthly costs based on active users
- Limited customization options
- External dependency
## Decision
**Chosen Option**: OAuth 2.0 with Auth0
### Rationale
1. Security expertise and compliance burden too high for custom solution
2. Auth0 provides enterprise-grade security features
3. Faster time to market
4. Cost is reasonable for projected user base
5. Team can focus on core business features
### Implementation Details
- Use Auth0 Universal Login for web authentication
- Implement Auth0 SDK for mobile applications
- Configure custom claims for tenant and role information
- Use Auth0 Actions for custom business logic
- Implement refresh token rotation for security
## Consequences
### Positive
- Reduced security risk and compliance burden
- Faster development cycle
- Professional-grade authentication UX
- Built-in features like MFA, social login
### Negative
- Ongoing subscription costs
- Vendor dependency
- Limited customization compared to custom solution
## Follow-up Actions
- [ ] Setup Auth0 tenant and initial configuration (Security Team, Week 1)
- [ ] Implement authentication flow in frontend (Frontend Team, Week 2-3)
- [ ] Configure API authorization middleware (Backend Team, Week 2)
- [ ] Setup monitoring and alerting for auth events (DevOps, Week 3)
Microservices vs Monolith
# ADR-003: Application Architecture Pattern
**Status**: Accepted
**Date**: 2024-01-25
**Authors**: Tech Lead, Senior Architects
**Reviewers**: Engineering Team, Product Team
## Context
Decide on the overall application architecture for a new e-commerce platform. Team size is 8 developers, expected to grow to 15 over the next year.
### Requirements
- Support rapid feature development
- Enable independent team deployment
- Handle seasonal traffic spikes (5x during holidays)
- Maintain system reliability and data consistency
- Allow for different technology choices per domain
## Considered Options
### Option 1: Monolithic Architecture
**Description**: Single deployable application with modular internal structure
**Pros**:
- Simpler deployment and operational model
- Easier debugging and testing
- Better performance for cross-domain operations
- Single codebase reduces complexity
- Lower infrastructure costs initially
**Cons**:
- Harder to scale development team
- Technology lock-in for entire application
- Difficult to scale individual components
- Risk of creating a "big ball of mud"
### Option 2: Pure Microservices
**Description**: Decompose application into many small, independent services
**Pros**:
- Independent team ownership and deployment
- Technology flexibility per service
- Fine-grained scaling
- Fault isolation
**Cons**:
- High operational complexity
- Distributed system challenges (networking, consistency)
- Team overhead for current size
- Difficult to maintain data consistency
### Option 3: Modular Monolith
**Description**: Single deployment with clear internal module boundaries
**Pros**:
- Clear separation of concerns
- Easier to extract services later
- Simple deployment model
- Shared infrastructure and tooling
**Cons**:
- Still shares some monolith limitations
- Requires discipline to maintain boundaries
- Single technology stack
## Decision
**Chosen Option**: Modular Monolith with Migration Path
### Rationale
1. Current team size doesn't justify microservices complexity
2. Modular structure provides clear boundaries for future extraction
3. Simpler operational model reduces risk
4. Can migrate to microservices as team grows
5. Better performance for initial feature set
### Implementation Details
- Structure application into clear domain modules
- Use dependency injection to enforce module boundaries
- Implement shared infrastructure components (auth, logging, etc.)
- Design APIs as if they were external services
- Plan extraction strategy for high-growth modules
### Migration Strategy
- Monitor module growth and team ownership patterns
- Extract to microservices when:
- Module has dedicated 3+ person team
- Independent scaling requirements emerge
- Different technology requirements arise
## Consequences
### Positive
- Faster initial development velocity
- Simpler testing and deployment
- Lower operational overhead
- Clear path to microservices when needed
### Negative
- Shared deployment pipeline
- Technology constraints across domains
- Requires architectural discipline
## Follow-up Actions
- [ ] Define module boundaries and interfaces (Architecture Team, Week 1)
- [ ] Setup module-based project structure (Tech Lead, Week 1)
- [ ] Create architectural guidelines document (Architecture Team, Week 2)
- [ ] Establish module ownership and review process (Team Leads, Week 2)
- [ ] Schedule quarterly architecture review (Product/Engineering, Ongoing)
ADR Best Practices
1. Writing Effective ADRs
Be Specific
- Include concrete technical details
- Provide measurable success criteria
- Reference specific technologies and versions
Show Your Work
- Document all seriously considered options
- Explain the decision-making process
- Include performance/cost analysis where relevant
Think Long-term
- Consider maintenance and evolution costs
- Document assumptions and constraints
- Plan for review and updates
2. ADR Lifecycle Management
Creation Process
- Identify architectural decision point
- Research options and gather input
- Write draft ADR with multiple options
- Review with relevant stakeholders
- Make decision and update ADR
- Communicate decision to team
Maintenance
- Review ADRs quarterly for relevance
- Update status when decisions change
- Create new ADRs when superseding old ones
- Archive outdated ADRs with clear status
3. ADR Integration with GISE
Discover Phase
- Document architectural constraints discovered
- Record stakeholder architectural preferences
- Identify architecture-influencing requirements
Design Phase
- Create ADRs for major architectural decisions
- Review and validate ADRs with stakeholders
- Use ADRs to guide detailed design decisions
Develop Phase
- Reference ADRs during implementation
- Update ADRs when implementation insights emerge
- Create new ADRs for significant technical choices
Deploy Phase
- Validate ADR assumptions against production behavior
- Document lessons learned and updates needed
- Plan ADR reviews and updates for next iteration