Legacy Single Page Application Modernization Evaluation

Role: Principal Web Architect specializing in large-scale enterprise web platform migrations.

Context

• Organization: {{company_name}}
• Current tech stack: {{legacy_stack}}
• Proposed modern framework: {{target_framework}}
• Identified system constraints: {{performance_bottlenecks}}
• Current engineering throughput: {{team_velocity_metrics}}
• High-impact operational areas: {{business_critical_routes}}

Task

Draft a comprehensive technical evaluation report that analyzes the feasibility, risk profile, and progressive rollout architecture for migrating the legacy web application to the target framework without disrupting active users.

Method

1. Parse {{legacy_stack}} state management and routing patterns against {{target_framework}} conventions.
2. Evaluate {{business_critical_routes}} to isolate mission-critical user workflows that require zero downtime.
3. Map {{performance_bottlenecks}} to architectural causes such as bundle bloat, hydration overhead, or memory leaks.
4. Design a strangler-fig coexistence model permitting simultaneous execution of legacy and new views.
5. Formulate a backward-compatible shared component library strategy across both framework boundaries.
6. Assess the impact on {{team_velocity_metrics}} during the transitional dual-maintenance phase.
7. Outline automated canary deployments, telemetry hooks, and fast-rollback triggers for web traffic.
8. Establish milestone-based deprecation gates to retire legacy assets systematically.

Constraints

• MUST prioritize zero regressions on {{business_critical_routes}}.
• MUST NOT recommend a full "big-bang" rewrite; all strategies must use incremental migration patterns.
• Recommendations must directly address the specific bottlenecks cited in {{performance_bottlenecks}}.
• Technical choices must accommodate the current developer skill sets documented in {{team_velocity_metrics}}.
• MUST provide clear acceptance criteria for each migration phase.

Output format

Generate a structured report with these exact sections:

1. Executive Technical Summary (150-200 words)
2. Architectural Migration Matrix (comparison table of legacy vs target paradigms)
3. Strangler Pattern Phasing Plan (Phase 0 through Phase 3 milestones)
4. Coexistence & State Sharing Strategy (mechanisms, risks, mitigations)
5. Developer Experience & Velocity Impact Analysis (150-250 words)

Self-review

• Have all 6 context variables been incorporated into the architectural trade-offs?
• Is the strangler-fig pattern realistic for {{legacy_stack}} transitioning to {{target_framework}}?
• Does the report strictly avoid recommending total rewrites?