SDLC Phase Gate

Validates that work meets criteria before moving between SDLC phases. Implements gates for: Requirements → Design → Implementation → Testing → Deployment → Operations.

Domain Context

Software lifecycle is a series of phases, each with distinct concerns and responsibilities:

Phase	Primary Role	Key Questions
Requirements	Product Manager	What problem are we solving? Is it worth solving?
Design	Architect	How will we solve it? What are the risks?
Implementation	Engineer	Can we actually build this?
Testing	QA	Does it work as designed?
Deployment	Tech Lead / Engineer	Is the rollout safe? Can we roll back?
Operations	Tech Lead	Is it stable in production? Can we respond to issues?

A phase gate ensures that before moving to the next phase, the current phase is sufficiently complete and the next phase has what it needs.

Phase gates are guardrails, not bureaucratic checkpoints. They catch misalignment early, when changes are cheap.

ISO/IEC 12207 Reference:

• 5.2.1 Stakeholder Needs and Requirements Definition
• 5.3.1 System Requirements Analysis
• 5.3.3 Architectural Design
• 5.3.4 Detailed Design
• 5.3.5 Implementation
• 5.3.6 Integration
• 5.3.7 Verification
• 5.3.8 Transition
• 5.3.9 Operation and Maintenance

Instructions

Step 1: Identify Current Phase and Work Item

• Input: Work item (feature, task, epic, release)
• Ask: What phase is this in? (Requirements, Design, Implementation, Testing, Deployment, Operations)
• Ask: What's the scope? (feature, bug fix, infrastructure, tech debt)

Step 2: Validate Current Phase Completion

For Requirements → Design Gate:

• Is the problem statement clear and agreed by all stakeholders?
• Is the success metric defined and measurable?
• Have edge cases and failure modes been identified?
• Has the security threat landscape been scoped?
• Is the scope bounded (no hidden assumptions)?

Output: Requirements completeness checklist

For Design → Implementation Gate:

• Has the system architecture been decomposed into components?
• Have trade-offs been explicitly documented (performance vs. complexity, flexibility vs. cost)?
• Has the security architecture been threat-modeled (STRIDE or equivalent)?
• Have dependency risks been identified (external services, rate limits, SLAs)?
• Has the accessibility design been reviewed?
• Is the design reviewable and approved by architect and security?

Output: Design completeness checklist

For Implementation → Testing Gate:

• Is the code complete for the feature (or slice)?
• Does the code follow team conventions and pass static analysis?
• Have unit tests been written and pass?
• Has the test strategy been defined (what will QA validate)?
• Are deployment rollback procedures documented?
• Have performance baselines been captured?

Output: Implementation readiness checklist

For Testing → Deployment Gate:

• Have all test scenarios passed (happy path, edge cases, error cases)?
• Has the test coverage met the team's threshold?
• Have security scans passed (SAST, dependency audit, secrets scan)?
• Have accessibility tests passed (WCAG, screen reader, keyboard navigation)?
• Have performance benchmarks met targets?
• Is the rollback procedure tested and documented?

Output: Testing completeness checklist

For Deployment → Operations Gate:

• Is the deployment plan approved by tech lead and ops?
• Is the rollout strategy clear (blue-green, canary, gradual)?
• Are monitoring and alerting configured?
• Is the runbook written (how to debug in production)?
• Have team members been trained on the feature?
• Is the incident response plan ready?

Output: Deployment readiness checklist

For Operations → Closure Gate:

• Is the feature stable in production (no critical alerts)?
• Are the monitoring metrics showing expected behavior?
• Have incident reports been reviewed and closed?
• Are there improvement items from operations feedback?
• Can the team move on to the next feature?

Output: Operations closure checklist

Step 3: Identify Blocking Issues

For each failed criterion:

• What's missing? (artifact, approval, test, documentation)
• Who owns fixing it? (architect, engineer, PM, security, QA, designer)
• How long to fix? (estimate in hours)
• Does it block the phase transition? (blocking, warning, informational)

Output: Blocking issues list with owners and estimates

Step 4: Make the Gate Decision

Go Decision:

• All blocking criteria are satisfied
• No critical risks remain unmitigated
• Next phase team has what it needs to succeed
• Document: "Gate approved, ready to transition"

Conditional Go Decision:

• Critical criteria are satisfied
• Non-critical criteria have acceptable workarounds
• Risk is documented and accepted
• Document: "Gate approved with accepted risks: [list]"

No-Go Decision:

• Critical criteria are not satisfied
• Risks cannot be mitigated in the next phase
• Recommend: Fix the issue in current phase
• Document: "Gate blocked. Required fixes: [list]. Re-evaluate in [timeframe]"

Step 5: Communicate the Decision

• To Current Phase Team: "Gate decision is [go/conditional/no-go]. [Issues to fix]. [Next steps]."
• To Next Phase Team: "You're cleared to proceed. Here's what you're inheriting: [scope, risks, dependencies]."
• To Leadership: "Feature [X] is [on track / at risk] for [target date]. Blocker: [if any]."

Anti-Patterns

1. Using phase gates to rubber-stamp completion

   • Mistake: "All checkboxes are checked, so the gate passes automatically"
   • Correct: Checklists inform the decision, but the decision is a judgment call
   • Fix: Require explicit human sign-off for go/no-go decisions

2. Making gates too early in the phase

   • Mistake: "Let's do the testing gate after the first sprint of development"
   • Correct: Gates should be at natural phase boundaries, when work is substantially complete
   • Fix: Define phase boundaries clearly; gate when "done" is achievable

3. Skipping gates because "we're fast"

   • Mistake: "Agile teams don't need phase gates, we ship continuously"
   • Correct: Continuous delivery still needs guardrails; gates work at sprint granularity
   • Fix: Apply phase gates to features or epics, not individual PRs

4. Treating gates as single-role decisions

   • Mistake: "The architect decides if design is complete"
   • Correct: Design completeness requires architect + security + engineer input
   • Fix: Make gates cross-functional; require sign-off from the role entering the phase

5. Not capturing risk and context

   • Mistake: "Gate passed, move on" (without documenting assumptions or risks)
   • Correct: Gate decisions should capture trade-offs and accepted risks
   • Fix: Always document: "This decision assumes [X]. If [Y] changes, re-evaluate."

6. Gates that are too strict

   • Mistake: "100% test coverage required; gates don't pass without it"
   • Correct: Thresholds should be evidence-based, not arbitrary
   • Fix: Define thresholds based on team data (velocity, defect rates, severity)

Further Reading

• ISO/IEC 12207 — Software lifecycle processes (Section 5.2, Process implementation)
• Stage-Gate Process — Cooper, R. G., "Winning at New Products" (Harvard Business Review Press)
• Lean Phase Gates — Reinertsen, D., "The Principles of Product Development Flow" (Celeritas Publishing)
• Risk Management in Phase Gates — PMI, "Project Management Institute Body of Knowledge" (PMBOK)