Legacy PHP migration is one of the most technically challenging and politically sensitive projects in software development. The system works. People depend on it. And every day it runs, it accumulates more technical debt.<\/p>\n
This is how we migrated a 10-year-old custom PHP application to Laravel 12 for a distribution company in Madhya Pradesh \u2014 without taking the system offline for a single hour.<\/p>\n
A mid-sized FMCG distribution company had been running a custom PHP 5.6 application since 2013. The system managed their entire operations \u2014 orders, inventory, billing, delivery tracking, and client accounts.<\/p>\n
By 2025, the system was showing its age:<\/p>\n
The business couldn’t stop using the system \u2014 40 staff used it daily, 200+ orders processed per day. A full rewrite with downtime was not an option.<\/p>\n
We used the Strangler Fig Pattern \u2014 gradually replacing the old system piece by piece while it remained live, until the old system could be safely retired.<\/p>\n
The approach:<\/p>\n
We spent the first three weeks doing nothing but understanding the existing system. No code changes. No new features.<\/p>\n
We mapped every page, every database table, every business rule. The existing system had no documentation \u2014 everything was implicit in the code.<\/p>\n
Key findings:<\/p>\n
Before touching the application, we hardened the database. This work applied to both the old and new system:<\/p>\n
-- Add missing indexes (the old system had almost none)\r\nALTER TABLE orders ADD INDEX idx_client_id (client_id);\r\nALTER TABLE orders ADD INDEX idx_created_at (created_at);\r\nALTER TABLE order_items ADD INDEX idx_order_id (order_id);\r\nALTER TABLE products ADD INDEX idx_sku (sku);\r\n\r\n-- Add foreign key constraints (previously missing)\r\nALTER TABLE order_items\r\n ADD CONSTRAINT fk_order_items_order\r\n FOREIGN KEY (order_id) REFERENCES orders(id) ON DELETE CASCADE;\r\n\r\n-- Fix inconsistent data before migration\r\nUPDATE orders SET status = 'pending' WHERE status IS NULL;\r\nUPDATE products SET stock_quantity = 0 WHERE stock_quantity IS NULL;<\/code><\/pre>\nThis work improved the old system’s performance immediately \u2014 query times on the orders list dropped from 4.2 seconds to 0.3 seconds just from adding indexes.<\/p>\n
Phase 3 \u2014 Laravel Setup with Shared Database (Weeks 6\u20138)<\/h2>\n
We set up the Laravel 12 application pointing at the same MySQL database as the old system. Laravel’s Eloquent models mapped to the existing table structure:<\/p>\n
\/\/ app\/Models\/Order.php \u2014 maps to existing orders table\r\nclass Order extends Model\r\n{\r\n \/\/ Use existing table structure\r\n protected $table = 'orders';\r\n\r\n \/\/ Map old column names to clean Laravel conventions\r\n protected $casts = [\r\n 'created_at' => 'datetime',\r\n 'order_date' => 'date',\r\n 'total_amount' => 'decimal:2',\r\n ];\r\n\r\n \/\/ Relationships that didn't exist in old system\r\n public function items(): HasMany\r\n {\r\n return $this->hasMany(OrderItem::class);\r\n }\r\n\r\n public function client(): BelongsTo\r\n {\r\n return $this->belongsTo(Client::class);\r\n }\r\n}<\/code><\/pre>\nPhase 4 \u2014 Module-by-Module Migration (Weeks 9\u201320)<\/h2>\n
We migrated modules in order of risk \u2014 lowest risk first, so we built confidence before touching critical features:<\/p>\n
\n\n\nWeek<\/th>\n Module Migrated<\/th>\n Risk<\/th>\n<\/tr>\n<\/thead>\n \n\n9\u201310<\/td>\n Reports and exports<\/td>\n Low (read-only)<\/td>\n<\/tr>\n \n11\u201312<\/td>\n Product catalogue<\/td>\n Low<\/td>\n<\/tr>\n \n13\u201314<\/td>\n Client management<\/td>\n Medium<\/td>\n<\/tr>\n \n15\u201316<\/td>\n Inventory tracking<\/td>\n Medium<\/td>\n<\/tr>\n \n17\u201318<\/td>\n Billing and invoices<\/td>\n High<\/td>\n<\/tr>\n \n19\u201320<\/td>\n Order management<\/td>\n Critical<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nFor each module migration, we used Nginx to route traffic:<\/p>\n
# nginx.conf \u2014 route reports to new Laravel system\r\nlocation \/reports {\r\n proxy_pass http:\/\/laravel_app;\r\n proxy_set_header Host $host;\r\n proxy_set_header X-Real-IP $remote_addr;\r\n}\r\n\r\n# Everything else still goes to old PHP system\r\nlocation \/ {\r\n root \/var\/www\/legacy;\r\n index index.php;\r\n fastcgi_pass php56:9000;\r\n}<\/code><\/pre>\nThe Hardest Part \u2014 Order Management Migration<\/h2>\n
The order management module was the most critical and the most complex. It had the most business logic, the most users, and processed \u20b915 lakh+ in transactions daily.<\/p>\n
We ran both systems in parallel for 2 weeks \u2014 every order written to the old system was also written to the new system via a sync job:<\/p>\n
\/\/ app\/Jobs\/SyncOrderToLaravel.php\r\nclass SyncOrderToLaravel implements ShouldQueue\r\n{\r\n public function __construct(public int $legacyOrderId) {}\r\n\r\n public function handle(): void\r\n {\r\n \/\/ Read from legacy format\r\n $legacyOrder = DB::table('orders_legacy_view')\r\n ->where('id', $this->legacyOrderId)\r\n ->first();\r\n\r\n \/\/ Transform and write to new format\r\n Order::updateOrCreate(\r\n ['legacy_id' => $legacyOrder->id],\r\n [\r\n 'client_id' => $legacyOrder->client_id,\r\n 'total_amount' => $legacyOrder->total,\r\n 'status' => $this->mapStatus($legacyOrder->status_code),\r\n 'order_date' => Carbon::parse($legacyOrder->order_dt),\r\n ]\r\n );\r\n }\r\n}<\/code><\/pre>\nAfter 2 weeks of parallel running with zero discrepancies, we switched the Nginx routing to direct all order traffic to Laravel.<\/p>\n
Phase 5 \u2014 Legacy Retirement (Week 21\u201322)<\/h2>\n
Once all modules were on Laravel, we kept the old system running in read-only mode for 2 weeks \u2014 just in case. Then we shut it down.<\/p>\n
Final state: PHP 5.6 application replaced with Laravel 12, zero downtime, zero data loss.<\/p>\n
Results<\/h2>\n
\n\n\nMetric<\/th>\n Before<\/th>\n After<\/th>\n<\/tr>\n<\/thead>\n \n\nAverage page load time<\/td>\n 4.8 seconds<\/td>\n 0.6 seconds<\/td>\n<\/tr>\n \nSecurity vulnerabilities<\/td>\n 2 critical, 8 medium<\/td>\n 0<\/td>\n<\/tr>\n \nServer errors per day<\/td>\n 15\u201320<\/td>\n 0\u20131<\/td>\n<\/tr>\n \nTime to onboard new developer<\/td>\n 2\u20133 weeks<\/td>\n 1\u20132 days<\/td>\n<\/tr>\n \nDeployment process<\/td>\n Manual FTP upload<\/td>\n Git push + CI\/CD<\/td>\n<\/tr>\n \nPHP version<\/td>\n 5.6 (EOL)<\/td>\n 8.3 (current)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nLessons Learned<\/h2>\n
Audit before you touch anything.<\/strong> Three weeks of reading code before writing any felt slow. It saved us from 3 major mistakes we would have made if we’d rushed.<\/p>\nDatabase first.<\/strong> Improving the database benefited both systems immediately and reduced the risk of data corruption during migration.<\/p>\nParallel running is worth the overhead.<\/strong> Running both systems simultaneously and comparing outputs for 2 weeks before cutover gave the client confidence and caught 2 edge cases we’d missed.<\/p>\nMigrate features, not code.<\/strong> We didn’t try to convert old PHP to Laravel line by line. We rebuilt each feature properly in Laravel. The result is cleaner and more maintainable.<\/p>\n