intent driven development
Week 3: Implementation
Based on the investigation and documentation, Alex coordinates a proof-of-concept extraction of the reporting service. This phase uses driver specs to coordinate multiple implementation steps.
The Implementation Pattern
Service extraction requires coordinated changes:
┌─────────────────────────────────────────────────────────────────┐
│ Driver Spec │
│ Reporting Service Extraction │
└─────────────────────────────────────────────────────────────────┘
│
┌─────────────────────┼─────────────────────┐
│ │ │
▼ ▼ ▼
┌─────────┐ ┌─────────┐ ┌─────────┐
│ API │ │Database │ │ Tests │
│ Extract │ │ Migrate │ │ Suite │
│ (.1) │ │ (.2) │ │ (.3) │
└────┬────┘ └────┬────┘ └────┬────┘
│ │ │
└─────────────────────┴─────────────────────┘
│
▼
┌─────────────────┐
│ Integration │
│ Testing │
│ (.4) │
└─────────────────┘
Creating the Driver Spec
Alex creates a driver spec for the extraction:
chant add "Extract reporting service POC" --type driver
File: .chant/specs/2026-02-01-001-ext.md
---
type: driver
status: pending
prompt: driver
depends_on:
- 2026-01-27-001-cpl # Coupling analysis
- 2026-01-28-001-doc # Architecture docs
informed_by:
- analysis/coupling/extraction-candidates.md
- analysis/coupling/risk-assessment.md
members:
- 2026-02-01-001-ext.1 # API extraction
- 2026-02-01-001-ext.2 # Database migration
- 2026-02-01-001-ext.3 # Test suite
- 2026-02-01-001-ext.4 # Integration testing
target_files:
- services/reporting/README.md
---
# Extract reporting service POC
## Problem
The reporting module is the best extraction candidate (score: 8.5/10):
- Zero incoming dependencies
- Clear API boundary
- Distinct resource profile
- Single team ownership
This POC extracts it as a standalone service to validate the approach.
## Extraction Steps
### Step 1: API Extraction (.1)
- Create new service repository structure
- Extract reporting endpoints
- Implement API gateway routing
- Output: Standalone reporting service
### Step 2: Database Migration (.2)
- Create read replica for reporting
- Set up denormalized views
- Configure connection pooling
- Output: Isolated data access
### Step 3: Test Suite (.3)
- Migrate existing reporting tests
- Add integration tests
- Create contract tests for API
- Output: Comprehensive test coverage
### Step 4: Integration Testing (.4)
- Test with monolith in parallel
- Verify data consistency
- Load test the new service
- Output: Validation report
## Execution Order
.1 (API) ──────────┐ │ .2 (Database) ─────┼───> .4 (Integration) │ .3 (Tests) ────────┘
.1, .2, .3 can run in parallel; .4 depends on all three.
## Acceptance Criteria
- [ ] All four member specs created
- [ ] Standalone service deployable
- [ ] All existing tests passing
- [ ] Integration tests passing
- [ ] Performance meets baseline
Member Specs
Member .1: API Extraction
File: .chant/specs/2026-02-01-001-ext.1.md
---
type: code
status: pending
parent: 2026-02-01-001-ext
informed_by:
- src/reporting/**/*.py
- docs/architecture/modules.md
target_files:
- services/reporting/src/main.py
- services/reporting/src/routes.py
- services/reporting/src/models.py
- services/reporting/Dockerfile
- services/reporting/pyproject.toml
---
# API extraction
## Problem
Extract reporting endpoints from monolith to standalone service.
## Tasks
- [ ] Create service structure
- [ ] Extract route handlers from `src/reporting/routes.py`
- [ ] Extract models (read-only copies)
- [ ] Configure FastAPI application
- [ ] Create Dockerfile for deployment
- [ ] Set up pyproject.toml with dependencies
## Acceptance Criteria
- [ ] Service starts and responds to health check
- [ ] All 5 reporting endpoints functional
- [ ] Same API contract as monolith
- [ ] Docker image builds successfully
Member .2: Database Migration
File: .chant/specs/2026-02-01-001-ext.2.md
---
type: code
status: pending
parent: 2026-02-01-001-ext
informed_by:
- src/reporting/models.py
- analysis/coupling/dependency-matrix.md
target_files:
- services/reporting/src/database.py
- services/reporting/migrations/001_initial.py
- infrastructure/reporting-replica.tf
---
# Database migration
## Problem
Reporting needs isolated data access without affecting monolith.
## Tasks
- [ ] Create read replica configuration
- [ ] Set up denormalized views for reporting queries
- [ ] Configure connection pooling (separate from monolith)
- [ ] Create Terraform for replica infrastructure
## Acceptance Criteria
- [ ] Read replica provisioned
- [ ] Reporting queries use replica (not primary)
- [ ] Query performance equal or better than baseline
- [ ] Zero impact on monolith database
Member .3: Test Suite
File: .chant/specs/2026-02-01-001-ext.3.md
---
type: code
status: pending
parent: 2026-02-01-001-ext
informed_by:
- tests/reporting/**/*.py
target_files:
- services/reporting/tests/test_routes.py
- services/reporting/tests/test_models.py
- services/reporting/tests/conftest.py
- services/reporting/tests/contracts/reporting_api.yaml
---
# Test suite
## Problem
Extracted service needs comprehensive tests.
## Tasks
- [ ] Migrate unit tests from `tests/reporting/`
- [ ] Create integration tests for new service
- [ ] Define contract tests (Pact-style)
- [ ] Set up test fixtures and conftest
## Acceptance Criteria
- [ ] All existing tests pass in new service
- [ ] Coverage >= 80%
- [ ] Contract tests verify API compatibility
- [ ] CI/CD pipeline runs tests
Member .4: Integration Testing
File: .chant/specs/2026-02-01-001-ext.4.md
---
type: task
status: pending
parent: 2026-02-01-001-ext
depends_on:
- 2026-02-01-001-ext.1
- 2026-02-01-001-ext.2
- 2026-02-01-001-ext.3
target_files:
- analysis/extraction/validation-report.md
---
# Integration testing
## Problem
Validate extracted service works correctly with rest of system.
## Tasks
- [ ] Deploy service alongside monolith
- [ ] Route 10% of reporting traffic to new service
- [ ] Compare response accuracy
- [ ] Measure latency and throughput
- [ ] Document findings
## Acceptance Criteria
- [ ] 100% response accuracy (vs monolith)
- [ ] P99 latency within 10% of baseline
- [ ] No errors under normal load
- [ ] Validation report complete
Running the Extraction
Alex executes the driver:
chant work 001-ext
Working: 2026-02-01-001-ext (Extract reporting service POC)
Phase 1: Parallel
[✓] 2026-02-01-001-ext.1 (API extraction) - 8m 22s
[✓] 2026-02-01-001-ext.2 (Database migration) - 12m 45s
[✓] 2026-02-01-001-ext.3 (Test suite) - 6m 18s
Phase 2: Sequential (depends on all above)
[✓] 2026-02-01-001-ext.4 (Integration testing) - 18m 30s
Driver complete. All 4 members succeeded.
Validation Report
File: analysis/extraction/validation-report.md (generated)
# Reporting Service Extraction - Validation Report
## Summary
| Metric | Baseline (Monolith) | Extracted Service | Status |
|--------|--------------------|--------------------|--------|
| P99 Latency | 2,400ms | 1,890ms | ✓ 21% improvement |
| Throughput | 45K req/day | 52K req/day capacity | ✓ Headroom |
| Error Rate | 0.08% | 0.06% | ✓ Slight improvement |
| Response Accuracy | — | 100% | ✓ All responses match |
## Test Results
| Test Suite | Pass | Fail | Skip |
|------------|------|------|------|
| Unit tests | 147 | 0 | 3 |
| Integration tests | 28 | 0 | 0 |
| Contract tests | 12 | 0 | 0 |
| Load tests | 5 | 0 | 0 |
Total: 192 passed, 0 failed, 3 skipped
## Performance Comparison
### P99 Latency by Endpoint
| Endpoint | Monolith | Extracted | Change |
|----------|----------|-----------|--------|
| /reports/daily | 1,850ms | 1,420ms | -23% |
| /reports/weekly | 2,400ms | 1,890ms | -21% |
| /reports/custom | 3,200ms | 2,650ms | -17% |
| /reports/export | 4,100ms | 3,200ms | -22% |
| /reports/schedule | 280ms | 245ms | -12% |
### Resource Usage
| Resource | Monolith (reporting) | Extracted | Change |
|----------|---------------------|-----------|--------|
| CPU | 78% | 65% | -17% |
| Memory | 52% | 48% | -8% |
| DB Queries | 28.6/req | 24.2/req | -15% |
## Parallel Running
Traffic split: 90% monolith, 10% extracted service
| Hour | Monolith Requests | Extracted Requests | Discrepancies |
|------|-------------------|-------------------|---------------|
| 00:00 | 1,890 | 210 | 0 |
| 01:00 | 1,620 | 180 | 0 |
| ... | ... | ... | 0 |
| 23:00 | 2,340 | 260 | 0 |
Total: 0 discrepancies in 24-hour parallel run
## Conclusion
Extraction successful. The POC validates:
1. Reporting can run as isolated service
2. Performance improves with dedicated resources
3. Zero data consistency issues
4. Test coverage is sufficient
### Recommendation
Proceed with production migration using gradual traffic shift:
- Week 1: 10% → 25%
- Week 2: 25% → 50%
- Week 3: 50% → 75%
- Week 4: 75% → 100%
Code Structure Created
The extraction created a new service structure:
services/
└── reporting/
├── src/
│ ├── main.py # FastAPI application
│ ├── routes.py # Extracted endpoints
│ ├── models.py # Read-only model copies
│ └── database.py # Replica connection
├── tests/
│ ├── test_routes.py # Unit tests
│ ├── test_models.py # Model tests
│ ├── conftest.py # Fixtures
│ └── contracts/
│ └── reporting_api.yaml
├── migrations/
│ └── 001_initial.py # Schema setup
├── Dockerfile
├── pyproject.toml
└── README.md
What’s Next
With the POC complete, Alex sets up ongoing maintenance:
Maintenance — Drift detection on documentation and metrics as code evolves