Skip to main content
Vibgrate Graph: over 27% fewer tokens in our benchmark
Playbook

Strangler-Fig Modernization Program Playbook

Replace a legacy system incrementally with the strangler-fig pattern. Route traffic through a facade, replace capabilities in waves with shadow testing, then strangle and decommission the legacy.

Difficulty
Advanced
Phases
4
Total Duration
33 weeks
Roles
5

The strangler-fig pattern replaces a legacy system gradually: new functionality grows around the old system, taking over capabilities one at a time, until the legacy is fully strangled and removed. This playbook runs that pattern as a long-lived program where the legacy keeps serving production until each replacement proves itself.

Phase-by-Phase

Facade and Routing Layer. Place a routing facade (typically an API gateway or reverse proxy) in front of the legacy system so traffic can be redirected per capability without callers noticing. Map the legacy endpoints and capture a metrics baseline.

Anti-Corruption and First Replacement. Build an anti-corruption layer that isolates the new code from the legacy data model. Replace the first capability and shadow-test it against the legacy by sending it real traffic without serving its responses, comparing outputs until confidence is high.

Incremental Replacement Waves. Replace capabilities in priority waves, shifting traffic progressively with canaries and feature flags, and retiring legacy modules as their replacements stabilize. The expand-and-contract pattern keeps data migrations safe across the dual-running period.

Final Strangle and Decommission. Once all traffic flows to the new system, remove the routing facade and decommission the legacy. Blameless postmortems on any incidents during cutover feed the runbooks.

Team and Roles

An architect owns the routing strategy and decision records. Backend engineers build replacements and the anti-corruption layer. DevOps and SRE run the gateway, traffic shifting, and observability. Product prioritizes capabilities by business value.

Risks and Mitigations

Dual-system consistency is the central risk while old and new run together; shadow testing and the expand-and-contract pattern keep data coherent. Routing complexity can grow unwieldy, so keep the facade configuration as code and well documented. Guard against scope creep by replacing along business value. Strong observability keeps the dual system debuggable.

Success Criteria

Success is a steadily falling percentage of traffic hitting the legacy, rising feature-delivery rate on the new system, and strong deployment frequency and MTTR. The legacy should be fully decommissioned at program end.

Tooling

Use a reverse proxy or API gateway for routing, Kubernetes for the new services, Kafka for integration events, PostgreSQL for new data stores, and Datadog or an equivalent for shadow-comparison and observability.

Category

Software Process

Tags

software processmodernizationlegacy migrationstrangler fig patternmicroservicesbest practices
Vibgrate CLI

See a real scan run

A replay of the actual CLI running against our test repositories — live progress, real findings, a genuine DriftScore. Nothing executes in your browser.

Replay
demo@vibgrate — bash
❯ npx @vibgrate/cli scan
 
╭──────────────────────────────────────────╮
│ Vibgrate Drift Report │
╰──────────────────────────────────────────╯
 
── node-turborepo (node) .
Runtime: >=18.0.0 (6 majors behind)
Frameworks:
Turbo: 1.13.4 → 2.10.12 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
1 current 1 1-behind 3 2+ behind 1 unknown
 
── @repo/admin (node) apps/admin
Frameworks:
TanStack Query: 5.102.5 → 5.102.5 (current)
React: 18.3.1 → 19.2.8 (1 behind)
React DOM: 18.3.1 → 19.2.8 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Vite: 5.4.21 → 8.2.2 (3 behind)
Dependencies:
3 current 9 1-behind 3 2+ behind 4 unknown
 
── @repo/api (node) apps/api
Frameworks:
Express: 4.22.2 → 5.2.1 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Vitest: 1.6.1 → 4.1.11 (3 behind)
Dependencies:
7 current 5 1-behind 3 2+ behind 4 unknown
 
── @repo/web (node) apps/web
Frameworks:
Next.js: 14.2.35 → 16.3.3 (2 behind)
React: 18.3.1 → 19.2.8 (1 behind)
React DOM: 18.3.1 → 19.2.8 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
2 current 6 1-behind 3 2+ behind 5 unknown
 
── @repo/config (node) packages/config
Frameworks:
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
2 current 2 1-behind 5 2+ behind 0 unknown
 
── @repo/database (node) packages/database
Frameworks:
Prisma: 5.22.0 → 7.10.0 (2 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
1 current 0 1-behind 3 2+ behind 1 unknown
 
── @repo/types (node) packages/types
Frameworks:
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Dependencies:
0 current 0 1-behind 1 2+ behind 1 unknown
 
── @repo/ui (node) packages/ui
Frameworks:
React: 18.3.1 → 19.2.8 (1 behind)
TypeScript: 5.9.3 → 7.0.2 (2 behind)
React: 18.3.1 → 19.2.8 (1 behind)
Dependencies:
1 current 4 1-behind 1 2+ behind 1 unknown
 
── @repo/utils (node) packages/utils
Frameworks:
TypeScript: 5.9.3 → 7.0.2 (2 behind)
Vitest: 1.6.1 → 4.1.11 (3 behind)
Dependencies:
0 current 1 1-behind 2 2+ behind 1 unknown
 
Tech Stack
Frontend: React, React DOM
Meta-frameworks: Next.js
Bundlers: tsx, Turbo, Vite
CSS / UI: Autoprefixer, PostCSS, Tailwind CSS
Backend: Express
ORM / Database: Prisma, Prisma Client
Testing: Vitest
Lint & Format: ESLint, ESLint Prettier, ESLint React, Prettier, typescript-eslint
 
Services & Integrations
Auth: JWT 9.0.3
Databases: Prisma 5.22.0
 
TypeScript
v5.3.3 · strict ✔ · MIXED · target: ES2022
 
Build & Deploy
Package Managers: pnpm
Monorepo: npm-workspaces, pnpm-workspaces, turbo
 
Product Purpose Signals
Frameworks: react, nextjs
Evidence: 177
Top Signals:
- [heading] Dashboard (apps/admin/src/pages/Dashboard.tsx)
- [title] Revenue Overview (apps/admin/src/pages/Dashboard.tsx)
- [copy] workspace:* (packages/ui/package.json)
- [copy] ./dist (packages/ui/tsconfig.json)
- [copy] ./src/index.ts (packages/ui/package.json)
- [copy] @repo/config/tsconfig-base.json (packages/ui/tsconfig.json)
- [copy] @repo/ui (packages/ui/package.json)
- [copy] #3b82f6 (apps/admin/src/pages/Dashboard.tsx)
Unknowns:
- No pricing or billing evidence found.
- No integrations/connectors evidence found.
- No route structure evidence found.
 
Security Posture
Lockfile ✖ · .env ✔ · node_modules ✔
 
Platform
Native modules: turbo
 
Code Quality
Files: 36 · Functions: 183 · Avg complexity: 2.62 · Avg length: 21.13 lines
Max nesting: 2 · Circular deps: 0 · Dead code: 0%
God files: apps/admin/src/pages/Products (448 lines)
 
Database Schema
postgresql · 8 models · 1 enum
Models: Address, CartItem, Category, Order, OrderItem (+3 more)
 
Findings (16 errors, 11 warnings)
✖ Node.js runtime ">=18.0.0" reached end-of-life on 2025-04-30 (latest: 24.0.0).
vibgrate/runtime-eol in .
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in .
✖ 60% of dependencies are 2+ major versions behind in node-turborepo.
vibgrate/dependency-rot in .
✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).
vibgrate/dependency-major-lag in .
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in apps/admin
✖ Vite is 3 major versions behind (current: 5.4.21, latest: 8.2.2).
vibgrate/framework-major-lag in apps/admin
✖ vite is 3 major versions behind (spec: ^5.0.12, latest: 8.2.2).
vibgrate/dependency-major-lag in apps/admin
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in apps/api
✖ Vitest is 3 major versions behind (current: 1.6.1, latest: 4.1.11).
vibgrate/framework-major-lag in apps/api
✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).
vibgrate/dependency-major-lag in apps/api
✖ vitest is 3 major versions behind (spec: ^1.2.1, latest: 4.1.11).
vibgrate/dependency-major-lag in apps/api
⚠ Next.js is 2 major versions behind (current: 14.2.35, latest: 16.3.3).
vibgrate/framework-major-lag in apps/web
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in apps/web
✖ @types/node is 6 major versions behind (spec: ^20.11.0, latest: 26.3.0).
vibgrate/dependency-major-lag in apps/web
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/config
✖ 56% of dependencies are 2+ major versions behind in @repo/config.
vibgrate/dependency-rot in packages/config
✖ eslint-plugin-react-hooks is 3 major versions behind (spec: ^4.6.0, latest: 7.1.1).
vibgrate/dependency-major-lag in packages/config
⚠ Prisma is 2 major versions behind (current: 5.22.0, latest: 7.10.0).
vibgrate/framework-major-lag in packages/database
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/database
✖ 75% of dependencies are 2+ major versions behind in @repo/database.
vibgrate/dependency-rot in packages/database
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/types
✖ 100% of dependencies are 2+ major versions behind in @repo/types.
vibgrate/dependency-rot in packages/types
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/ui
⚠ TypeScript is 2 major versions behind (current: 5.9.3, latest: 7.0.2).
vibgrate/framework-major-lag in packages/utils
✖ Vitest is 3 major versions behind (current: 1.6.1, latest: 4.1.11).
vibgrate/framework-major-lag in packages/utils
✖ 67% of dependencies are 2+ major versions behind in @repo/utils.
vibgrate/dependency-rot in packages/utils
✖ vitest is 3 major versions behind (spec: ^1.2.1, latest: 4.1.11).
vibgrate/dependency-major-lag in packages/utils
 
╭──────────────────────────────────────────╮
│ Top Priority Actions │
╰──────────────────────────────────────────╯
 
1. Upgrade EOL runtime in node-turborepo
End-of-life runtimes no longer receive security patches and block ecosystem upgrades.
./.
>=18.0.0 → 24.0.0 (6 majors behind)
Impact: −10 drift points (runtime & EOL)
 
2. Fix security posture: no lockfile found
Without a lockfile, installs are non-deterministic. Run the install command to generate one and commit it.
./
Missing: package-lock.json, pnpm-lock.yaml, or yarn.lock
 
3. Upgrade Vite 5.4.21 → 8.2.2 in @repo/admin (+2 more)
3 major versions behind. Major framework drift increases breaking change risk and blocks access to security fixes and performance improvements.
./apps/admin
Vite: 5.4.21 → 8.2.2 (3 majors behind)
./apps/api
Vitest: 1.6.1 → 4.1.11 (3 majors behind)
./packages/utils
Vitest: 1.6.1 → 4.1.11 (3 majors behind)
Impact: −5–15 drift points
 
4. Reduce dependency rot in @repo/types (100% severely outdated)
1 of 1 dependencies are 2+ majors behind. Run `npm outdated` and prioritise packages with known CVEs or breaking API changes.
./packages/types
typescript: 5.9.3 → 7.0.2 (2 majors behind)
Impact: −5–10 drift points
 
5. Reduce dependency rot in @repo/database (75% severely outdated)
3 of 4 dependencies are 2+ majors behind. Run `npm outdated` and prioritise packages with known CVEs or breaking API changes.
./packages/database
@prisma/client: 5.22.0 → 7.10.0 (2 majors behind)
prisma: 5.22.0 → 7.10.0 (2 majors behind)
typescript: 5.9.3 → 7.0.2 (2 majors behind)
Impact: −5–10 drift points
 
╭──────────────────────────────────────────╮
│ Architecture Layers │
╰──────────────────────────────────────────╯
 
Archetype: nextjs (80% confidence)
Files classified: 24 (11 unclassified)
Folders classified: 8
apps/admin/src presentation 100% 4 files
apps/admin/src/pages presentation 100% 2 files
apps/api/src/middleware middleware 100% 2 files
apps/api/src/routes routing 100% 2 files
apps/web/src/app presentation 100% 4 files
apps/web/src/app/products presentation 100% 2 files
apps/web/src/app/products/[id] presentation 100% 1 file
packages/ui/src presentation 100% 6 files
Unclassified source (sample): 11
 
presentation 15 files drift ████████████████████ 100 risk high
routing 4 files drift ████████████████████ 100 risk high
middleware 2 files drift ███████▍░░░░░░░░░░░░ 37 risk moderate
config 2 files drift ░░░░░░░░░░░░░░░░░░░░ 0 risk none
shared 1 file drift ████████████████████ 100 risk high
 
╭──────────────────────────────────────────╮
│ DriftScore Summary │
╰──────────────────────────────────────────╯
 
DriftScore: 66/100
Risk Level: HIGH
Projects: 9
Classified: 8 nano · 1 micro · 0 small · 0 standard
Billable: 0.42 · 9 detected → 0.42 billable projects (micro-project pricing)
0.1 micro · 0.32 nano
These fractions add up across repositories, then round down to whole billable projects.
 
Score Breakdown
Runtime: ████████████████████ 100
Frameworks: █████████▏░░░░░░░░░░ 46
Dependencies: ██████▏░░░░░░░░░░░░░ 31
EOL Risk: ████████████████████ 100
 
Scanned at 2026-08-26T09:08:28.481Z · 7.1s · 286 files scanned · 56 workspace files · 27 dirs
❯
Press Run to start.
Explore the Vibgrate CLI