Building a Custom WMS + ERP Solution - A Deep Dive into My Most Ambitious Project

Introduction

Developing a custom Warehouse Management System (WMS) and Enterprise Resource Planning (ERP) solution for a fresh food wholesale and delivery supplier targeted to gastronomy remains one of my most ambitious and technically challenging projects to date. What started as a critical system failure at the company evolved into an opportunity to build a scalable, high-performance, and fully customized solution from the ground up.

This journey tested my skills in software architecture, full-stack development, database optimization, system integration, and performance engineering. Despite the obstacles, the final product was a robust, extensible, and cost-effective system that continues to serve the company’s operations today.

The Project’s Origin: Why Build Instead of Buy?

The existing third-party WMS + ERP system suffered from frequent crashes, scalability limitations, and high licensing costs. The search for off-the-shelf replacements revealed that adapting commercial solutions to fit the company’s specialized workflow would be both costly and inefficient.

Having previously worked in multiple roles within the company—including network administration, IT infrastructure management, website maintenance, and social media marketing—I was well-acquainted with its operational needs. Recognizing an opportunity, I proposed an in-house, custom-built alternative that would:

• Perfectly align with business processes without unnecessary features.
• Reduce operational costs by eliminating licensing fees and third-party dependencies.
• Ensure scalability and extensibility for future growth and integration needs.
• Offer full control over data security, system performance, and compliance.

With my boss’s support, I embarked on this transformative journey.

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Key Features & Technical Innovations

1. High-Performance Architecture for Peak Loads

The business operates under two major peak periods:

• Order placement: A two-hour afternoon window where customers submit bulk orders.
• Order fulfillment: A three-to-four-hour early morning window when orders are processed and shipped, reaching hundreds requests per second.

Solution: Advanced Caching Strategies

To prevent database bottlenecks, I implemented multi-layered caching using Redis, significantly reducing response times and database load. This approach included:

• Query-level caching for frequently accessed data.
• Session caching for user authentication and permissions.
• Precomputed aggregation caching for real-time analytics.

These optimizations ensured that the system remained highly responsive even during peak usage.

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2. Smart Inventory & Pricing Management

The biggest challenge was designing a real-time stock reservation and dynamic pricing system that mimicked a Dutch flower auction model:

• As new stock arrives, customers must be able to reserve inventory dynamically.
• Pricing adjusts based on demand, stock availability, and customer-negotiated rates.
• Inventory updates occur in real-time while fulfilling orders, requiring a highly synchronized transaction system.

Solution: Optimized Transactional Consistency

• Implemented database-level locking and transaction logs to prevent overselling.
• Designed an event-driven architecture using Redis Pub/Sub for real-time updates.
• Created a backorder queue system for customers to reserve out-of-stock items automatically.

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3. Seamless Compliance & Financial Integration

Ensuring full compliance with Polish financial and tax regulations was crucial. By collaborating with the company’s accountant, I:

• Integrated automated invoicing and VAT calculations.
• Developed auditable transaction logs for inventory movements and financial reporting.
• Implemented custom fiscal reports tailored to legal and operational requirements.

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4. Mobile-Optimized Operations for Delivery Staff

Warehouse staff and delivery drivers required mobile access for:

• Barcode scanning for inventory management.
• Offline order processing during deliveries in areas with poor internet connectivity.
• Electronic proof of delivery (ePOD) with digital signatures and real-time order status updates.

Solution: Progressive Web App (PWA) with Offline Mode

Instead of developing a native mobile app, I built a fully responsive web application using:

• Service Workers & IndexedDB for offline capabilities.
• Barcode scanning API integration for streamlined warehouse operations.
• Optimized UI components for mobile usability, ensuring fast navigation.

This approach minimized maintenance complexity while offering near-native performance.

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The Tech Stack: Choosing the Right Tools for the Job

Backend:

• Node.js + Express.js (switched from Django for flexibility and TypeScript compatibility).
• PostgreSQL as the primary database for ACID-compliant transactions.
• Redis for ultra-fast caching and session management.
• Docker for containerized deployment.
• RBAC-based authentication system using JWT & session-based auth.

Frontend:

• React + React Router for a Single Page Application (SPA) experience.
• Redux (later migrated to Zustand & React Query) for state management.
• Chart.js for real-time analytics visualization.
• Custom UI components & MUI for rapid UI development.

Infrastructure & DevOps:

• Self-hosted Ubuntu Server with Docker Compose.
• Automated database backups (RAID 1, cloud & external storage redundancy).
• Zero-trust remote access using Cloudflare tunneling.

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Lessons Learned & Major Takeaways

1. Caching is King

The database quickly became the primary bottleneck, and while scaling PostgreSQL horizontally was an option, clever caching strategies provided a much more efficient and cost-effective solution.

2. The Reality of Time Estimation

A common rule of thumb in software development is to double your initial time estimate. In this case, my initial estimate was off by a factor of 3–4x. This experience reinforced the importance of:

• Breaking down tasks into smaller, more estimable components.
• Allocating time for unexpected complexities.

3. Building Alone vs. Working in Teams

While solo development allowed for full control and deep technical learning, a team would have accelerated delivery through parallel development and knowledge sharing. In future large-scale projects, I would prioritize collaborative development methodologies.

4. The Right Tool for the Right Job

• PostgreSQL > NoSQL for structured, transactional data.
• Zustand > Redux for better state management simplicity.
• REST API was a better long-term fit than GraphQL for this use case.

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Reflections on the Journey: The Cost of Ambition

Completing this project was a journey that spanned several dozen months, filled with countless challenges, long hours, and many sleepless nights. The level of dedication required to bring this vision to life pushed me to my limits—both technically and physically.

Throughout the process, I had to solve incredibly complex problems, often working late into the night to ensure that every aspect of the system was optimized, secure, and scalable. Debugging intricate issues, refining performance bottlenecks, and architecting a solution that could withstand real-world operational demands took an immense toll. Every decision mattered, every line of code had an impact, and every mistake was a learning opportunity.

Looking back, I can confidently say that it was worth it. The satisfaction of seeing a fully functional, real-world system actively helping a business thrive is beyond rewarding. I gained invaluable experience in full-stack development, system architecture, database optimization, and business process automation. The lessons I learned during this time continue to shape how I approach software development today.

However, despite the success, I’ve come to a firm conclusion: I would never take on such an ambitious project solo again. Not because I lack the skill or determination, but because the cost—physically, mentally, and emotionally—is too high. Health is something you only get once, and burnout is a very real risk in large-scale solo development.

That being said, if the opportunity ever arose to work on something of this scale again within a well-structured team, I would absolutely consider it. Collaborating with other skilled developers, sharing the workload, and maintaining a healthier work-life balance would make all the difference.

So, while this project remains a career-defining achievement, it also serves as a personal reminder: No matter how passionate you are, sustainability matters.

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Conclusion: A Career-Defining Experience

This project was a transformative milestone in my career. It challenged me to think beyond basic CRUD applications and delve into scalable architectures, high-performance optimizations, and real-world business logic implementation.

The resulting system is a cost-efficient, scalable, and business-critical solution that continues to streamline the company’s operations today. More importantly, it reinforced my passion for solving complex problems with technology—a passion that continues to drive my work to this day.

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