Payment System Scalability

In 2023, UPI processed over 100 billion+ transactions, that’s a level of scalability and efficiency that many just wish to achieve. India’s UPI system is a giant example of how a great distributed system should work at scale with efficiency. I read a 30+ page PDF by the Govt. Of Indian  and spent 4 hours researching the architecture behind UPI, here are my learnings: 1. Modular and Centralized Architecture   UPI uses a hub-and-spoke model, with NPCI at the center handling clearing and settlement. Banks, fintechs, and payment service providers (PSPs) integrate via APIs, creating a plug-and-play ecosystem.  - Centralized Hub: Manages routing, fraud checks, and settlements.   - Decentralized Nodes: Banks and PSPs handle user interactions.  This design scales horizontally, enabling quick feature rollouts like UPI Lite for small transactions and UPI AutoPay for recurring payments. 2. API-Driven Scalability  UPI’s RESTful APIs support stateless communication, ensuring requests don’t depend on prior sessions, perfect for horizontal scaling.  - 10,000+ Transactions Per Second (TPS): Built for concurrency, even during high loads.   - Asynchronous Processing: Keeps transactions fast without blocking resources.   - Microservices Architecture: Enables modular updates without downtime.  3. Proxy-Based Identity Management  UPI eliminates the need for exposing sensitive bank details by using Virtual Payment Addresses (VPAs) and QR codes.  - Aliases Over Accounts: Payments rely on VPAs, maintaining privacy.   - Interoperable QR Codes: Scan-and-pay functionality ensures merchant adoption with minimal hardware.   - Device Binding: Prevents unauthorized access by linking devices securely.  4. Security-First Approach  Security is baked into UPI with multi-layered encryption and real-time fraud detection.  - Two-Factor Authentication (2FA): Ensures secure transactions with PINs and device binding.   - AI-Driven Fraud Detection: Uses machine learning to block suspicious activities in real-time.   - Tokenization: Protects sensitive data, reducing exposure to breaches.  5. Open Standards and Interoperability  UPI supports open APIs and ISO 20022 standards, making integration seamless.  - Legacy System Support: Connects old banking systems via modular adapters.   - Cross-Border Payments: Integrated with Singapore’s PayNow and expanding globally.   - Batch and Real-Time Processing: Supports both micro and bulk transactions.  UPI is a case study in scalable distributed systems. It demonstrates how to:  1. Design stateless APIs for high-concurrency systems.   2. Build modular architectures for seamless feature updates.   3. Optimize real-time data processing while maintaining security.   4. Ensure interoperability for future-proofing systems.

🚀 Scaling a Monolithic Transactional System from 1× to 100× for 10K+ TPS Scaling a monolithic transactional system to handle 10,000+ transactions per second isn’t just about adding servers — it’s about architectural evolution. Here’s the scaling journey I recommend: 1️⃣ Optimize the Monolith (1× → 5×) 1. Optimize DB queries & indexes 2. Introduce in-memory caching (Redis/Memcached) 3. Use connection pooling & batch processing 2️⃣ Scale Vertically (5× → 10×) 1. Bigger instances, more RAM & faster disks 2. Improve GC tuning & runtime configurations 3. Use asynchronous I/O for heavy network calls 3️⃣ Horizontal Scaling (10× → 25×) 1. Deploy multiple instances behind a load balancer 2. Stateless app layer, shared DB 3. Read replicas for DB reads 4️⃣ Database Sharding & Partitioning (25× → 50×) 1. Split data by key (e.g., customer ID, region) 2. Dedicated shards reduce lock contention 3. Async replication & eventual consistency where possible 5️⃣ Microservices & Event-Driven Architecture (50× → 100×) 1. Break critical flows into smaller, independent services 2. Use Kafka/Pulsar for async event streaming 3. Enable polyglot persistence for specialized workloads 🎯 End State: A distributed, fault-tolerant, horizontally scalable system that can process 10K+ TPS while keeping latency low and availability high. 💡 Key Tip: Don’t jump from 1× to 100× overnight — scale in stages, measure, and optimize. #SystemDesign #Scalability #Architecture #EngineeringLeadership #DistributedSystems #HighAvailability

Razorpay: What It Takes to Make Payments That Never Fail Payment failures don’t just ruin transactions. They ruin trust. And yet, Razorpay processes millions of transactions daily, through festivals, sales, and surge traffic, with barely a hiccup. During Diwali sales or Big Billion Days, while most systems gasp for air, Razorpay quietly handles the load like clockwork. That level of stability doesn’t come from luck. It comes from architecture built for chaos. A few years ago, even large payment systems in India struggled during spikes. Servers would timeout. APIs would choke. Transactions would fail halfway, customers lost money, merchants lost faith. Razorpay changed the game by doing something deceptively simple: They stopped treating payments as single transactions, and started treating them as distributed, fault-tolerant events. Here’s how: 1: Multi-Gateway Redundancy No single point of failure. Every payment request can reroute through multiple gateways. If one gateway is slow or down, the transaction is instantly retried through another, without user awareness. 2: Smart Retry Queues Failed transactions aren’t abandoned. They’re queued, retried, and reconciled automatically. The system doesn’t depend on users pressing “Try Again.” 3: Layered Verification Each transaction passes through multiple validation checks, user, merchant, and gateway level. This ensures consistency even when external APIs misfire or return delayed confirmations. 4: Real-Time Monitoring & Rollbacks Razorpay constantly monitors gateway health and success rates. If a sudden drop occurs, it automatically shifts traffic to stable gateways and logs rollback operations for traceability. 5: Predictive Load Scaling Before large events, the system scales itself preemptively, not reactively. The platform knows when traffic is coming and adjusts capacity before the first payment hits. The result? Even under festival-level load, users see one thing, a success screen. Reliability isn’t a feature. It’s a promise. Every failed payment isn’t just a bug, it’s a broken customer experience. And once trust breaks, code can’t fix it. Good systems don’t just process payments. They protect them. #Tech #SystemDesign #ScalableSystems #Fintech #Payments #Engineering #Kaifoundry #Razorpay

Yesterday, Mookh — the ticketing platform meant to sell Chan tickets — went down under load. This isn’t new: high-demand ticket drops often expose weak system design. The lessons are old, but they bear repeating. 1. Reservations are non-negotiable When a user selects a ticket, reserve it for 2 minutes. Mark it as “temporarily unavailable” (not sold). If payment doesn’t clear in time, release it. This prevents overselling but still captures intent. 2. Traffic ≠ downtime if you plan ahead You can scale up EC2 instances or, if you like orchestration complexity, Kubernetes. Both give you elasticity, but one is a black box and the other is YAML therapy. Either way, build for traffic spikes, don’t pray for them. 3. Background work doesn’t belong in the request cycle Email confirmations, PDF ticket generation, notifications — push them to queues. That way, a 502 doesn’t mean an email never goes out. Kafka, RabbitMQ, even Redis Streams — just don’t tie heavy lifting to user-facing endpoints. 4. Modular from day 1 A monolith is fine — a modular monolith is better. Keep ticketing, auth, payments, notifications separated in code so you can later scale them independently. Example: PDF rendering is CPU-bound, video encoding is GPU-bound, signup logic barely uses resources. Provision differently. 5. Thou shall not go serverless Don’t be tempted by “just one more function bro.” Cloud functions are seductive, but they’ll leave you with an incomprehensible architecture and an invoice that kills your runway. Even Big Tech teams get burned by serverless bills. If you take anything away: start with a modular monolith. Separation of concerns is the foundation of scalable systems. Mookh’s collapse is a reminder: tech is only as good as its architecture.

💳 Payment Wallet Architecture — What Really Happens Behind “Pay” in 2 Seconds? Everyone talks about “real-time payments”… Very few understand the orchestration behind that single tap. I recently designed a full-scale Payment Wallet System Architecture — not just boxes & arrows, but the actual thinking layer behind scalability, reliability, and compliance. Here’s what most people miss 👇 ⸻ ⚙️ 1. It’s NOT just an API call A simple “Pay” triggers: • Auth + risk checks • Ledger consistency (double-entry) • Idempotent transaction orchestration • Bank / network integrations • Event streaming + async reconciliation ⸻ 🏗️ 2. The real backbone = Ledger + Events Forget UI, forget APIs. If your ledger is weak → your system is broken. • Real-time balance ≠ actual settlement • Event-driven architecture ensures auditability • Every state change is immutable ⸻ 🛡️ 3. Fraud & Risk are FIRST-class citizens Not an afterthought. • Device fingerprinting • Velocity checks • Behavioral scoring • Dynamic rule engines 👉 Payments don’t fail because of tech. They fail because of trust gaps. ⸻ 🌐 4. External systems are the biggest bottleneck Banks. Networks. Gateways. They: • Timeout • Retry inconsistently • Break SLAs So your system must: • Be resilient by design • Support async fallbacks • Handle partial failures gracefully ⸻ 🔁 5. Reconciliation is where truth lives End-of-day ≠ end of system. • Wallet ≠ Bank balance • Automated + manual reconciliation • Exception queues are critical 👉 If you can’t reconcile, you don’t own your money flow. ⸻ 🚨 6. Failure is the default state Design for: • Retries with backoff • Circuit breakers • Saga-based compensations • Idempotency everywhere ⸻ 📊 7. Observability is non-negotiable If you can’t trace a transaction across: API → Service → Queue → Bank → Ledger You’re blind. ⸻ 💡 Closing Analysis Building a payment wallet is not a feature. It’s a distributed, regulated, real-time financial system where every millisecond and every cent matters. ⸻ #SystemDesign #DistributedSystems #SoftwareArchitecture #ScalableSystems #HighAvailability #BackendEngineering #CloudComputing #Microservices #EventDrivenArchitecture #APIDesign #FinTech #PaymentSystems #DigitalPayments #RealTimePayments #BankingTechnology #UPI #CardPayments #RiskManagement #FraudDetection #LedgerSystems #EngineeringLeadership #TechLeadership #PlatformEngineering #ReliabilityEngineering #SRE #DevOps #ResilientSystems #ProductionSystems #SystemThinking #DesignPatterns #SoftwareEngineer #TechCommunity #BuildInPublic #EngineeringExcellence #TechInsights #StartupEngineering #BigTech #Innovation #LearnInPublic #CareerGrowth #wallet #founders #startups #architects

💡 𝗦𝘁𝗿𝗮𝘁𝗲𝗴𝘆 + 𝗣𝗹𝘂𝗴𝗶𝗻 𝗗𝗲𝘀𝗶𝗴𝗻 𝗣𝗮𝘁𝘁𝗲𝗿𝗻𝘀 + 𝗗𝗗𝗗 Integrating multiple payment methods like PayPal and Stripe into an e-commerce platform can be tricky. With the Strategy and Plugin patterns, you can make the process much more flexible, extensible, and maintainable. Here's how: 𝟭. 𝗦𝘁𝗿𝗮𝘁𝗲𝗴𝘆 𝗣𝗮𝘁𝘁𝗲𝗿𝗻: Interchangeable Payment Methods •  Each payment method (PayPal, Stripe) follows a common IPaymentMethod interface. The PaymentService delegates the payment processing task to the appropriate payment method. •  How It Follows SOLID: 𝗦𝗶𝗻𝗴𝗹𝗲 𝗥𝗲𝘀𝗽𝗼𝗻𝘀𝗶𝗯𝗶𝗹𝗶𝘁𝘆: Each payment method focuses solely on processing payments. 𝗢𝗽𝗲𝗻/𝗖𝗹𝗼𝘀𝗲𝗱: You can easily add new payment methods without altering existing code. 𝗟𝗶𝘀𝗸𝗼𝘃 𝗦𝘂𝗯𝘀𝘁𝗶𝘁𝘂𝘁𝗶𝗼𝗻: You can swap payment methods without breaking anything. 𝗜𝗻𝘁𝗲𝗿𝗳𝗮𝗰𝗲 𝗦𝗲𝗴𝗿𝗲𝗴𝗮𝘁𝗶𝗼𝗻: The interface is focused, with no unnecessary methods. 𝗗𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝗰𝘆 𝗜𝗻𝘃𝗲𝗿𝘀𝗶𝗼𝗻: The PaymentService depends on the abstraction (IPaymentMethod), not the concrete implementation. 𝟮. 𝗣𝗹𝘂𝗴𝗶𝗻 𝗣𝗮𝘁𝘁𝗲𝗿𝗻: 𝗗𝘆𝗻𝗮𝗺𝗶𝗰 𝗣𝗮𝘆𝗺𝗲𝗻𝘁 𝗠𝗲𝘁𝗵𝗼𝗱𝘀 •  Payment methods are implemented as plugins, loaded at runtime based on user input or configuration. •  Why It Follows 𝗖𝗹𝗲𝗮𝗻 Architecture: 𝗦𝗲𝗽𝗮𝗿𝗮𝘁𝗶𝗼𝗻 𝗼𝗳 𝗖𝗼𝗻𝗰𝗲𝗿𝗻𝘀: Payment logic is isolated, keeping the core system clean. 𝗠𝗼𝗱𝘂𝗹𝗮𝗿 𝗗𝗲𝘀𝗶𝗴𝗻: Payment methods are independent modules, easy to extend and maintain. 𝟯. 𝗛𝗼𝘄 𝗜𝘁 𝗙𝗶𝘁𝘀 𝘄𝗶𝘁𝗵 𝗗𝗗𝗗 (𝗗𝗼𝗺𝗮𝗶𝗻-𝗗𝗿𝗶𝘃𝗲𝗻 𝗗𝗲𝘀𝗶𝗴𝗻) •  Bounded Contexts: Each payment method (PayPal, Stripe) has its own distinct processing rules within its bounded context. •  Ubiquitous Language: Clear and consistent language around payment functionality. •  Aggregate Roots: Payment transactions are treated as aggregates, ensuring consistency. 𝟰. 𝗕𝗲𝗻𝗲𝗳𝗶𝘁𝘀 •  Scalability & Flexibility: Easily add or swap payment methods. •  Maintainability: Isolated payment logic makes updates and testing easier. •  SOLID Adherence: High cohesion, low coupling, and extensibility for future changes. 𝟱. 𝗧𝘂𝗿𝗻𝗶𝗻𝗴 𝘁𝗵𝗲 𝗣𝗮𝘆𝗺𝗲𝗻𝘁 𝗠𝗼𝗱𝘂𝗹𝗲 𝗶𝗻𝘁𝗼 𝗮 𝗠𝗶𝗰𝗿𝗼𝘀𝗲𝗿𝘃𝗶𝗰𝗲 The loosely coupled and modular design of the payment modules enables them to evolve into microservices with these steps: 𝗗𝗲𝗰𝗼𝗺𝗽𝗼𝘀𝗲 𝘁𝗵𝗲 𝗦𝗲𝗿𝘃𝗶𝗰𝗲: The payment module becomes its own microservice, handling all payment methods internally. 𝗔𝗣𝗜 𝗚𝗮𝘁𝗲𝘄𝗮𝘆: Route requests to the right payment microservice. 𝗘𝘃𝗲𝗻𝘁-𝗗𝗿𝗶𝘃𝗲n: Use event-driven communication (like RabbitMQ or Kafka) to decouple services. 𝗦𝗰𝗮𝗹𝗮𝗯𝗹𝗲 & 𝗜𝗻𝗱𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝘁: Each payment service can scale independently. Disclaimer: I'm not claiming this is the 'best' way, just the way I thought of it. Feel free to roast my solution and offer better ones! #DotNet #DesignPatterns #DDD #CleanArchitecture #Microservices

Most issuer processors say they have “robust infrastructure.” We learned the hard way what that really means. Years ago, when we were building our first company (Privacy.com), we worked with several of the most established legacy processors and kept hitting the limits as we scaled: 🕒 scheduled downtime 📊 messy settlement reporting 🐢 years for basic feature releases 🙈 consistently lackluster support It was painful. And it became clear: if we wanted a highly performant and resilient platform, we’d have to build it ourselves. That’s how Lithic started. Our mission to transform payments and banking infrastructure has always been personal for us. In his latest post, my cofounder Jason breaks down how we built a platform that delivers: ✅ 99.999%+ authorization uptime 💳 Billions in monthly volume 🏗️ 100+ programs The difference is in the details: ⚡️ Multiple redundant private circuits into Visa, Mastercard, and the Federal Reserve. The entire internet could be down, and we will continue to route and process transactions. 💪 N+3 redundancy across fully independent data centers 🧠 Real-time auth intelligence, that enables better fraud detection, and flexible ledger architecture We built with intentionality because we’d seen firsthand what breaks as you scale. The architectural and choices we made (hybrid cloud, physical connectivity, Rust/DynamoDB stack) are about removing the constraints that make modern card issuing processing so difficult to scale reliably. If you’re evaluating payment infrastructure, Jason’s post lays out some key questions: 💭 Are they directly connected to the networks or routing through gateways? 🌐 Do they use dedicated fiber or depend on the public internet? ⚙️ Can their architecture support real-time processing and next-gen account types? The choice is simple: 👉 Build on 2025 infrastructure or 🚧 Get stuck with 2015 limitations And if you’re heading to Money20/20 and made it this far, come say hi! 👇 Full breakdown in Jason’s post in comments.

Banks don’t fail at payments because of volume. They fail because payments are treated as features, not as a platform. In many banks, payment journeys still look like this: 👉 Channel → Core Banking → Rail This architecture works when volumes were low and rails were few. It breaks in a world of UPI, IMPS, RTP, ISO 20022, fraud velocity, and regulatory scrutiny. 🔑 Modern banks win with a STRONG PAYMENTS HUB A Payments Hub is not a gateway. It is the control plane of money movement. What a strong Payments Hub enables: * One orchestration layer for all rails (UPI, IMPS, RTGS, NEFT, Cards, SWIFT) * Core banking protected as system of record — not transaction router * Real-time fraud, AML, limits & velocity checks * ISO 20022 translation without core rework * Clean audit trails, reversals, retries & reconciliation * Faster innovation without touching the core every time 💡 Golden rule: Channels should never talk to core directly. Gateways should never bypass orchestration. The Payments Hub must sit in between — always. Banks that design payments as capability, not a project, scale safely. Those that don’t keep adding patches… until the system collapses under load. Payments are no longer plumbing. They are strategic infrastructure. #BankingArchitecture #PaymentsHub #CoreBanking #UPI #ISO20022 #DigitalTransformation #FinTech #EnterpriseArchitecture #BankingTechnology

In 2011, Wise started with just 2 employees.   Today, it’s a 1000+ employee company across 9 cities and 4 continents.  How did they scale their technical infrastructure to support this massive growth? Let’s dive into the technical strategies that powered their journey.  1️⃣ Autonomous, Agile Teams for Scalable Development      - Independent teams focused on specific domains (e.g., payments, user accounts).   - Teams owned the lifecycle of their services: design, development, testing, and operations.  ► Impact:   - Enabled parallel development and reduced bottlenecks.   - Faster iterations through decentralized decision-making.   - Specialized teams delivered depth and innovation.  2️⃣ Building Microservices for Modular Scalability      - Adopted microservices to decouple functionalities like currency exchange and payment processing.   - Leveraged RESTful APIs and asynchronous communication.  ► Impact:   - Independent deployment and scaling of services.   - Fault isolation ensured one service’s failure didn’t disrupt the system.   - Simplified adding new features without core system disruption.  3️⃣ Leveraging Data-Driven Insights for Optimization    - Built data pipelines to analyze real-time customer transactions and behavior.   - Used tools like Apache Kafka for event streaming and ElasticSearch for log analysis.  ► Impact:   - Optimized currency routing and reduced transfer times.   - Enhanced fraud detection using predictive analytics.   - Continuous feedback loops improved user experience.  4️⃣ Prioritizing Global Infrastructure for Real-Time Operations    - Deployed globally distributed servers and data centers for low latency.   - Tailored infrastructure for handling multiple currencies and jurisdictions.  ► Impact:   - Real-time money transfers across 750+ currency routes.   - Reduced downtime with redundancy and failover systems.   - Complied with local financial regulations globally.  5️⃣ Scaling the Payments System for Volume and Reliability    - Built a resilient system to handle millions of transactions daily.   - Introduced retries, idempotency keys, and eventual consistency.  ► Impact:   - Seamlessly handled growing transaction volumes.   - Ensured data integrity and prevented transaction failures.   - Delivered a high-availability service customers could trust.  6️⃣ Borderless Account: User-Centric Engineering    - Developed a multi-currency account platform for holding, converting, and transferring 28 currencies.   - Integrated local bank systems for seamless transactions.  ► Impact:   - Minimized conversion fees using real-time rates.   - Enabled global payments with virtual account numbers.   - Simplified currency management for individuals and businesses.  7️⃣ Culture of Experimentation and Ownership - Empowered engineers with end-to-end service ownership.   - Encouraged experimentation and innovative ideas.    - Built custom tools like internal monitoring systems and deployment pipelines.

Why Merchants Who Treat Payments the Same Everywhere Struggle to Scale Any merchant who has had to deal with expanding their business globally knows that it isn't as simple as just offering some new payment methods, but rather that it is about understanding how each region prefers to pay and then optimizing to accommodate customers to do that. However, I still frequently talk to merchants who think that having the "essential" payment options, such as credit cards, PayPal, or maybe a digital wallet, is enough to go global. In reality, local nuance matters far more than you’d expect. According to McKinsey & Company, over 70% of global e-commerce growth stems from regional payment preferences. Think Klarna in the Nordics, iDeal in the Netherlands, and Pix in Brazil. Missing these nuances is like speaking the wrong language: you can offer the “right” payment methods, but still lose customers who don’t see their preferred local approach. As a Payments Strategist, I’ve frequently worked with merchants who invested heavily in marketing to expand internationally, only to stumble at checkout because they treated all customers the same. But why is that? Let me explain... What most merchants often get wrong is: Overlooking local behavior. Some regions have a high adoption of specific e-wallets or cash-based vouchers. Sticking only to global card brands can lead to cart abandonment. One-size-fits-all fraud checks. Global fraud patterns don’t translate cleanly across borders. A strict rule set for Europe could create false declines in Latin America, where the IP and device profiles differ. Difficulty in scaling operationally. Managing multiple gateways, local acquirers, or alternative payments can become an operational nightmare. Without the right orchestration layer, you end up with scattered data and inconsistent reconciliation. Missing out on better approval rates. Visa and Mastercard have both reported higher authorization rates in cross-border transactions when merchants adopt local processing or network tokens. The solution? Focus on regional optimization, not just “adding more payment methods.” Payment orchestration platforms (like IXOPAY) enable merchants to tailor routing, tokenization, and risk checks to each market. That means higher approval rates, fewer false declines, and better customer experiences—no matter where your shoppers are. Personally, I see local payment strategies as the final piece of the puzzle for a true global scale. Having multiple methods at checkout is essential. Knowing how people want to pay and implementing the technology to support is what ultimately drives growth and revenue. What do you think? Are local payment preferences the hidden barrier to global expansion, or are merchants focusing too much on niche payment methods? Let me know in the comments. P.S. Check out my newsletter for more Payments Strategy Breakdowns https://buff.ly/IDbkSLw