ADR Decision Drivers

Decision drivers are the forces, concerns, and requirements that influence architectural decisions. Identifying and documenting these drivers clearly is essential for creating ADRs that explain not just what was decided, but why.

What Are Decision Drivers?

Decision drivers are factors that:

• Constrain the solution space
• Prioritize certain qualities over others
• Represent stakeholder concerns
• Create tension requiring trade-offs

Categories of Decision Drivers

Category	Description	Examples
Functional	What the system must do	Features, capabilities, integrations
Quality Attributes	How well system must perform	Performance, security, reliability
Constraints	Fixed limitations	Budget, timeline, technology mandates
Business	Organizational factors	Cost, time-to-market, compliance
Technical	Engineering considerations	Maintainability, testability, complexity
Team	Human factors	Skills, capacity, preferences

Identifying Decision Drivers

Discovery Questions

Ask these questions to uncover drivers:

Functional Drivers

• What must this system do?
• What capabilities are essential vs nice-to-have?
• What integrations are required?

Quality Attribute Drivers

• What are the performance requirements?
• How critical is availability?
• What are the security requirements?
• How important is scalability?

Constraint Drivers

• What is the budget?
• What is the timeline?
• What technologies are mandated?
• What regulations apply?

Business Drivers

• What is the cost sensitivity?
• How important is time-to-market?
• What is the risk tolerance?
• What competitive factors matter?

Technical Drivers

• How complex can the solution be?
• What is the expected maintenance burden?
• How important is extensibility?
• What testing requirements exist?

Team Drivers

• What skills does the team have?
• What capacity is available?
• What are team preferences?
• What training would be needed?

Quality Attributes (The "-ilities")

Core Quality Attributes

Attribute	Definition	Measures
Performance	Response time, throughput	Latency (ms), requests/sec
Scalability	Handle increased load	Concurrent users, data volume
Availability	System uptime	Percentage uptime, MTBF
Reliability	Correct operation	Error rate, MTTR
Security	Protection from threats	Vulnerabilities, compliance
Maintainability	Ease of changes	Change effort, code complexity
Testability	Ease of testing	Test coverage, test time
Usability	User experience	Task completion time, errors

Extended Quality Attributes

Attribute	Definition	Measures
Portability	Run on different platforms	Platform support, migration effort
Interoperability	Work with other systems	Integration points, standards
Modifiability	Support changes	Change impact, coupling
Observability	Monitor system state	Metrics, logs, traces
Deployability	Ease of deployment	Deployment frequency, time
Recoverability	Recovery from failure	RTO, RPO

Documenting Decision Drivers

Format for Driver Documentation

## Decision Drivers

* **{Driver Name}** - {Brief description of the driver and why it matters}
* **{Driver Name}** - {Brief description}

Good Driver Documentation

## Decision Drivers

* **High availability required** - System must maintain 99.9% uptime as per SLA
* **Limited budget** - Total solution cost must not exceed $50K/year
* **Team lacks Kubernetes expertise** - Any container orchestration must be learnable quickly
* **Compliance with GDPR** - User data must be stored in EU region
* **Sub-100ms response time** - API latency critical for user experience

Poor Driver Documentation

## Decision Drivers

* Performance
* Cost
* Easy to use

Problems: Too vague, no specifics, no prioritization

Prioritizing Drivers

MoSCoW Method

Priority	Meaning	Treatment
Must	Non-negotiable	Solution must satisfy
Should	Important	Satisfy if possible
Could	Nice to have	Include if easy
Won't	Out of scope	Explicitly excluded

Ranking Approach

List drivers in order of importance:

1. {Most critical driver}
2. {Second most important}
3. {Third priority} ...

Weighted Scoring

Assign weights to drivers:

Driver	Weight (1-5)
Availability	5
Performance	4
Cost	3
Maintainability	2

Trade-off Analysis

Identifying Trade-offs

Common quality attribute trade-offs:

Trade-off	Description
Performance vs Maintainability	Optimized code harder to maintain
Security vs Usability	More security often means more friction
Scalability vs Cost	Scaling often increases infrastructure cost
Flexibility vs Simplicity	Configurable systems are more complex
Speed vs Quality	Faster delivery may reduce quality

Documenting Trade-offs

### Trade-offs Accepted

We accept:
- **Higher infrastructure cost** for improved availability
- **Increased complexity** for better extensibility
- **Longer initial development** for lower maintenance burden

Using Drivers in Options Evaluation

Evaluation Matrix

Option	Driver 1	Driver 2	Driver 3	Score
Option A	++	+	-	4
Option B	+	++	+	5
Option C	-	+	++	4

Scoring: ++ (2), + (1), 0 (0), - (-1), -- (-2)

Qualitative Evaluation

For each option, evaluate against each driver:

### Option 1: PostgreSQL

* **High availability**: Good - supports replication, mature tooling
* **Limited budget**: Moderate - open source but requires expertise
* **Team expertise**: Good - team has SQL experience

Common Pitfalls

Avoid These Mistakes

1. Missing drivers - Failing to identify all relevant factors
2. Vague drivers - "Performance" instead of "sub-100ms response time"
3. No prioritization - Treating all drivers as equal
4. Ignoring constraints - Forgetting budget, timeline, compliance
5. Technology bias - Letting preferred tech drive requirements
6. Single perspective - Not gathering input from all stakeholders

Driver Discovery Workshops

Stakeholder Input

Gather drivers from:

• Product owners (business requirements)
• Architects (technical requirements)
• Operations (operational requirements)
• Security team (security requirements)
• Users (usability requirements)

Workshop Questions

1. What would make this decision successful?
2. What would make it fail?
3. What constraints must we work within?
4. What quality attributes matter most?
5. What trade-offs are acceptable?
6. What risks concern you?

Additional Resources

Reference Files

For comprehensive guidance on specific aspects:

• references/quality-attributes.md - Detailed quality attribute definitions
• references/trade-off-patterns.md - Common trade-off patterns and resolutions

Related Skills

• adr-fundamentals - ADR basics and lifecycle
• adr-quality - Quality review criteria
• adr-format-madr - MADR format with decision drivers section
• adr-compliance - Auditing code against ADR decisions