Monolith to Modular Architecture Migration Planner

=== MONOLITH ARCHITECTURE ASSESSMENT ===

Application
RevenueHub

Technology stack
Laravel monolith with MySQL, Redis queues, Stripe integration, Blade admin screens, jobs, events, and shared helpers.

Current architecture
Large MVC monolith with mixed responsibilities across controllers, Eloquent models, service classes, jobs, model events, and shared helper functions.

Data provided
Route list, model list, service list, database schema, partial tests, and deployment notes. No full dependency graph, runtime traces, or complete test coverage report were provided.

Primary pain points

1. Billing and subscription renewal are business-critical but weakly tested.
2. Notification logic is spread across multiple entry points.
3. Reporting queries are slow and coupled directly to many tables.
4. Shared database access creates hidden dependencies.
5. Manual deployment and limited rollback increase migration risk.
6. The team wants microservices, but the current test and deployment maturity suggest modular monolith should come first.

Recommended target architecture
Modular monolith first, with selective service extraction later.

Why this target
The system has weak test coverage, shared database coupling, and high-risk revenue workflows. Immediate microservice extraction would increase operational complexity and production risk. A modular monolith allows the team to create clearer boundaries, reduce coupling, add tests, and prepare for future service extraction without changing deployment topology too early.

Bounded context candidates

1. Billing

Business responsibility
Subscriptions, invoices, payment renewal, Stripe interaction, payment state, plan logic.

Core entities
subscriptions, invoices, payments, plans, users

Owned data candidate
subscriptions, invoices, payments, plans

Current code locations
Billing-related controllers, subscription services, payment jobs, invoice generators, Stripe integration code, Eloquent models.

Inbound dependencies
Checkout, user accounts, admin operations, order workflows.

Outbound dependencies
Stripe, email notifications, CRM, reporting.

Coupling level
High

Extraction readiness
Low

Risks
Revenue-critical logic, payment integration, renewal jobs, shared user data, weak tests, no downtime tolerance.

Recommended first step
Do not extract Billing first. Add characterization tests around subscription purchase, renewal, invoice generation, failed payment handling, and Stripe webhook processing. Introduce a PaymentGateway interface before deeper refactoring.

2. Notifications

Business responsibility
Customer emails, transactional notifications, event-driven communication, notification preferences, delivery logs.

Core entities
notifications, templates, delivery logs, user preferences if present.

Owned data candidate
notifications and delivery logs.

Current code locations
Mailers, jobs, model events, controllers, shared notification helpers.

Inbound dependencies
Billing, orders, users, admin operations.

Outbound dependencies
Email provider, possibly CRM.

Coupling level
Medium

Extraction readiness
High

Risks
Many scattered call sites, duplicate templates, possible hidden behavior in model events.

Recommended first step
Inventory all notification call sites, add characterization tests for major notification flows, create a NotificationSender facade, and route one low-risk notification through it.

3. Reporting

Business responsibility
Admin reports, exports, analytics summaries, operational reporting.

Core entities
report_exports, read queries across orders, users, subscriptions, invoices, payments.

Owned data candidate
report_exports and derived read models.

Current code locations
Admin controllers, report services, export jobs, direct SQL/Eloquent queries.

Inbound dependencies
Admin users and scheduled jobs.

Outbound dependencies
CSV exports, analytics tools, possibly email delivery.

Coupling level
Medium to high

Extraction readiness
Medium

Risks
Direct cross-table reads, slow queries, unclear data freshness requirements.

Recommended first step
Document all reporting queries, classify reports by business value and performance cost, create read-only reporting interfaces, and avoid direct writes to core domain tables.

4. Orders

Business responsibility
Order creation, order state, checkout-related records, order lifecycle.

Core entities
orders, users, payments, subscriptions if linked.

Coupling level
High

Extraction readiness
Low to medium

Risks
Potential coupling with billing, users, checkout, notifications, and reporting.

Recommended first step
Map order lifecycle and transaction boundaries before extraction.

5. Users

Business responsibility
Account identity, login, profile, permissions, customer ownership.

Core entities
users, roles, permissions, profiles

Coupling level
Critical

Extraction readiness
Low

Risks
Usually shared across almost every domain. Extracting too early can destabilize authentication, authorization, billing, reporting, admin screens, and notifications.

Recommended first step
Document user model usage and reduce direct user model access where possible.

=== EXTRACTION CANDIDATE PRIORITIZATION ===

First candidates

1. Notifications

Priority
High

Reason
Notifications can often be isolated behind an interface and later made event-driven. It has commercial and operational value, but lower core transaction risk than billing.

First safe step
Create an inventory and add tests before moving logic.

2. Reporting

Priority
Medium to high

Reason
Reporting is a good candidate if it is mostly read-only. It can be separated gradually through read models, query objects, or reporting interfaces.

First safe step
Document report queries and create read-only reporting boundaries.

3. External integration adapters

Priority
Medium

Reason
Stripe, email, CRM, and analytics should be isolated behind clear interfaces. This reduces coupling and improves testability.

First safe step
Introduce adapter interfaces without changing behavior.

Do not extract yet

Billing
Too revenue-critical and weakly tested.

Users
Too widely shared and usually foundational.

Orders
Likely tied to billing, checkout, notifications, and reporting. Needs lifecycle mapping first.

=== MODULAR MIGRATION ROADMAP ===

Target architecture
Modular monolith first, with selective service extraction later.

Migration strategy
Use incremental modularization, characterization tests, facades, branch by abstraction, dependency reduction, and staged extraction. Preserve the existing deployment model until boundaries, tests, observability, and team ownership are mature.

Phase 0 — Discovery and architecture inventory:

Goals

• Create a route, controller, model, job, event, service, and table inventory.
• Map business capabilities.
• Identify notification, billing, reporting, order, and user workflows.
• Document external integrations.
• Identify critical revenue paths.

Tasks

• Generate a file tree and module inventory.
• List all billing-related routes, controllers, models, services, and jobs.
• List all notification call sites.
• List all reporting queries.
• Map database tables to candidate domains.
• Document deployment and rollback process.

Exit criteria

• Key business capabilities are mapped.
• Critical workflows are documented.
• High-risk areas are identified.

Phase 1 — Safety baseline:

Goals

• Protect current behavior before refactoring.
• Reduce production risk.

Tasks

• Add characterization tests for subscription purchase, renewal, invoice generation, Stripe webhook handling, order creation, and notification sending.
• Add smoke tests for login, checkout, subscription renewal, admin report access, and email delivery.
• Add logging around failed renewal jobs and notification delivery.
• Define manual rollback steps.

Exit criteria

• Critical workflows have baseline tests.
• Deployment smoke checks exist.
• Rollback procedure is documented.

Phase 2 — Internal module boundaries:

Goals

• Create modular structure without changing deployment.

Proposed modules

• app/Modules/Billing
• app/Modules/Orders
• app/Modules/Notifications
• app/Modules/Reporting
• app/Modules/Users
• app/Modules/Integrations

Tasks

• Create module READMEs.
• Move no behavior initially.
• Document owned entities and dependencies.
• Introduce facades and interfaces for notifications, payments, reporting, and CRM.

Exit criteria

• Module boundaries are documented.
• Initial interfaces exist.
• No behavior change has occurred.

Phase 3 — Dependency reduction:

Goals

• Reduce direct cross-domain calls.

Tasks

• Route notification sending through NotificationSender.
• Move email template formatting into Notifications module.
• Introduce PaymentGateway interface around Stripe.
• Introduce ReportingQueryService for admin reports.
• Replace direct helper usage with module-level interfaces where safe.

Exit criteria

• Low-risk dependencies are behind interfaces.
• Notification logic is centralized.
• Reporting queries are documented behind a read-only boundary.

Phase 4 — Data ownership preparation:

Goals

• Make database ownership explicit before service extraction.

Tasks

• Assign candidate owners for subscriptions, invoices, payments, orders, users, notifications, and report_exports.
• Identify cross-domain writes.
• Stop new direct writes across boundaries.
• Introduce read models or query interfaces for reporting.
• Protect billing transactions from accidental boundary changes.

Exit criteria

• Table ownership map exists.
• Cross-domain write risks are documented.
• No critical transaction is changed without tests.

Phase 5 — Candidate extraction:

Goals

• Extract low-risk modules first.

Candidate 1:
Notifications internal module

Candidate 2:
Reporting read module

Candidate 3:
Integration adapters

Tasks

• Move notification behavior behind stable facade.
• Add events for non-critical notification triggers where useful.
• Move report generation into reporting module.
• Isolate external integration adapters.

Exit criteria

• Selected module behavior is test-protected.
• Rollback path exists.
• Monitoring confirms no production regression.

Phase 6 — Optional service extraction:

Goals

• Extract only if justified by team ownership, scaling, deployment, or operational needs.

Possible service candidates

• Notifications service
• Reporting service
• Search or export service if added later

Do not extract first

• Billing
• Users
• Core order lifecycle

Exit criteria

• API contracts exist.
• Contract tests exist.
• Observability is ready.
• On-call ownership is defined.
• Deployment automation is mature.

=== AI CODING AGENT MODERNIZATION PLAN ===

Operating constraints

• Do not perform broad rewrites.
• Do not change production behavior unless explicitly requested.
• Do not change database schema in early tasks.
• Do not alter billing behavior without tests.
• Do not remove legacy code until replacement behavior is verified.
• Every task must be small, reviewable, and reversible.

Task 1:

Title
Inventory notification entry points.

Objective
Find all mailers, jobs, model events, controllers, services, and helpers that send customer notifications.

Allowed changes
Documentation only.

Forbidden changes
No production code changes.

Tests
None required.

Validation
Produce a notification call-site inventory.

Rollback
No rollback needed.

Risk
Low

Human review
Yes

Task 2:

Title
Add characterization tests for notification sending.

Objective
Capture current notification behavior before moving logic.

Allowed changes
Add tests only.

Forbidden changes
No behavior changes.

Tests
Add tests for order confirmation, subscription renewal notification, failed payment notification, and account email notification.

Validation
Tests pass against current behavior.

Rollback
Remove the test branch if needed.

Risk
Low

Human review
Yes

Task 3:

Title
Create NotificationSender interface.

Objective
Introduce a single internal boundary for sending notifications.

Allowed changes
Add interface/facade and wire one low-risk notification through it.

Forbidden changes
No template changes. No delivery timing changes. No database schema changes.

Tests
Existing notification tests must pass.

Validation
Selected notification still sends as before.

Rollback
Revert usage of the facade for the selected notification.

Risk
Medium

Human review
Yes

Task 4:

Title
Inventory billing critical flows.

Objective
Document all controllers, services, jobs, events, models, and integrations involved in billing and subscription renewal.

Allowed changes
Documentation only.

Forbidden changes
No production code changes.

Tests
None required.

Validation
Produce a billing flow map.

Risk
Low

Human review
Yes

Task 5:

Title
Add characterization tests for subscription renewal.

Objective
Protect the most important billing behavior before refactoring.

Allowed changes
Add tests only.

Forbidden changes
No production code changes.

Tests
Subscription renewal success, failed payment, invoice creation, webhook handling.

Validation
Tests pass against current behavior.

Risk
Medium

Human review
Yes

=== TEST STRATEGY ===

Critical workflows

• account registration
• login
• subscription purchase
• payment renewal
• failed payment handling
• invoice generation
• order creation
• notification sending
• admin report access

Characterization tests
Add first for billing, orders, notifications, and reporting.

Unit tests
Add around extracted business rules and adapters.

Integration tests
Add for database-backed billing, order, and reporting workflows.

Contract tests
Add later when module APIs or service boundaries are introduced.

End-to-end tests
Cover checkout, renewal, and admin reporting.

Smoke tests
Run after every deployment.

Release gate
No extraction should proceed unless critical characterization tests pass and rollback steps are documented.

=== RISK REGISTER ===

High risk
Billing and subscription renewal changes could affect revenue.

High risk
Shared user model is a dependency across many domains.

Medium risk
Reporting queries may depend on many tables and undocumented assumptions.

Medium risk
Notification behavior may be scattered across events, jobs, and controllers.

Medium risk
Manual deployment creates rollback uncertainty.

Mitigation
Start with inventory, tests, facades, and low-risk module boundaries before extraction.

=== JSON MIGRATION PLAN ===

{
  "application": "RevenueHub",

"technology_stack": "Laravel monolith with MySQL, Redis queues, Stripe integration, and Blade admin screens",
"target_architecture": "modular monolith first, selective service extraction later",

  "bounded_contexts": [
    {
      "name": "Billing",

  "business_responsibility": "subscriptions, invoices, payment renewal, plans, Stripe integration",

      "core_entities": [
        "subscriptions",
        "invoices",
        "payments",
        "plans"
      ],
      "owned_data": [
        "subscriptions",
        "invoices",
        "payments",
        "plans"
      ],
      "current_code_locations": [
        "billing controllers",
        "subscription services",
        "payment jobs",
        "invoice generators",
        "Stripe integration code"
      ],
      "dependencies": [
        "users",
        "orders",
        "notifications",
        "Stripe",
        "reporting"
      ],
      "coupling_level": "high",
      "extraction_readiness": "low",
      "risks": [
        "revenue-critical behavior",
        "weak tests",
        "shared user data",
        "payment integration risk"
      ],

  "first_safe_step": "Add characterization tests and introduce PaymentGateway interface."

    },
    {
      "name": "Notifications",

  "business_responsibility": "transactional notifications, templates, delivery behavior, notification logs",

      "core_entities": [
        "notifications",
        "templates",
        "delivery logs"
      ],
      "owned_data": [
        "notifications",
        "notification delivery logs"
      ],
      "current_code_locations": [
        "mailers",
        "jobs",
        "model events",
        "controllers",
        "notification helpers"
      ],
      "dependencies": [
        "users",
        "orders",
        "billing",
        "email provider"
      ],
      "coupling_level": "medium",
      "extraction_readiness": "high",
      "risks": [
        "scattered call sites",

    "hidden behavior in model events"
  ],
  "first_safe_step": "Inventory notification call sites and introduce NotificationSender facade."

    }
  ],
  "migration_phases": [
    {
      "phase": "Phase 0",

  "name": "Discovery and architecture inventory",

      "goals": [
        "map business capabilities",

    "inventory routes, controllers, models, jobs, events, services, and tables",
    "identify critical workflows"

      ],
      "tasks": [
        "generate architecture inventory",
        "map billing flows",
        "map notification call sites",
        "map reporting queries"
      ],
      "risks": [
        "incomplete dependency visibility"
      ],
      "exit_criteria": [
        "business capabilities documented",
        "critical workflows documented",
        "high-risk areas identified"
      ]
    },
    {
      "phase": "Phase 1",
      "name": "Safety baseline",
      "goals": [

    "protect critical behavior before refactoring"

      ],
      "tasks": [
        "add characterization tests",
        "add smoke tests",
        "define rollback process"
      ],
      "risks": [

    "tests may reveal undocumented behavior"

      ],
      "exit_criteria": [
        "critical workflows have tests",
        "rollback procedure documented"
      ]
    }
  ],
  "ai_coding_tasks": [
    {

  "title": "Inventory notification entry points",
  "objective": "Find all code paths that send notifications.",

      "allowed_changes": [
        "documentation only"
      ],
      "forbidden_changes": [
        "production code changes"
      ],
      "tests": [],
      "risk_level": "low",
      "human_review_required": true
    },
    {

  "title": "Add characterization tests for subscription renewal",
  "objective": "Capture current billing behavior before refactoring.",

      "allowed_changes": [
        "add tests"
      ],
      "forbidden_changes": [
        "behavior changes",
        "database schema changes"
      ],
      "tests": [
        "subscription renewal success",
        "failed payment",
        "invoice creation",
        "webhook handling"
      ],
      "risk_level": "medium",
      "human_review_required": true
    }
  ]
}