PulseFit - Cross-Platform Mobile SaaS App
End-to-End Flutter iOS & Android App with Node.js REST API Backend
The Business & Technical Problem
The founding team needed to launch an interactive fitness coaching and workout telemetry subscription app on both iOS and Android simultaneously. Maintaining separate Swift and Kotlin native codebases exceeded budget runway. Furthermore, gym basements frequently experienced complete cellular dropouts, causing workout logging failures and user churn in earlier prototypes.
Delivered Scope & Responsibilities
Architected unified cross-platform Flutter mobile client with BLoC state pattern and low-latency Node.js API.
Engineered Node.js & Express REST API handling authentication, subscription entitlements, and workout telemetry.
Designed Flutter UI with custom 60fps animation controllers, responsive tablet layouts, and custom charts.
Modeled PostgreSQL relational schemas with foreign key integrity and Redis caching for active user sessions.
Implemented secure JWT token rotation, Apple Sign-In compliance, and Google OAuth.
Automated GitHub Actions CI/CD building signed IPA and AAB release binaries for Store submission.
Integrated Sentry mobile crash monitoring, Firebase Cloud Messaging (FCM), and automated error logging.
Architecture Decisions, Rejected Alternatives & Accepted Trade-Offs
Flutter with BLoC State Management instead of React Native
Flutter's compiled Skia/Impeller engine guarantees predictable 60fps rendering without JavaScript bridge serialization bottlenecks during real-time sensor updates.
React Native was rejected due to bridge thread stutters observed during rapid timer/sensor telemetry ticks.
Slightly larger compiled mobile application binary footprint (~18MB vs ~12MB native).
Hive Local Key-Value Store with Atomic Sync Queue
Allowed users to record multi-set workouts in offline gym basements with zero UI latency, syncing automatically when connectivity returned.
SQLite was evaluated but Hive provided faster read/write serialization for rapid telemetry logging.
Required building custom client-side conflict resolution logic for workout log timestamps.
Backend Webhook Billing Engine for Stripe & In-App Purchases
Validating subscription receipts strictly on the Node.js backend prevented client-side entitlement spoofing and simplified invoice reconciliation.
Client-only in-app purchase listeners.
Required asynchronous webhook retry queuing to withstand intermittent payment gateway webhook delivery delays.
Measured Project Outcomes
Every metric specifies the measurement environment, method, and Abin's contribution. Unverified benchmarks are not presented as contractual SLAs.
| Metric Name | Baseline | Final Value | Environment | Measurement Method | Abin's Contribution |
|---|---|---|---|---|---|
| UI Frame Rate Consistency | 38-44 fps (React Native prototype) | 60 fps locked | Lab | Flutter DevTools Performance Overlay on mid-tier Android device (Snapdragon 680)(Q1 2025) | Restructured widget tree using BlocSelector and const constructor widgets to isolate rebuilds. |
| API P99 Response Time | 120ms | 14ms | Production | Datadog APM tracing on workout sync endpoints(2024 - 2025) | Implemented Redis read-caching and compound PostgreSQL indexing on user telemetry tables. |
| App Store Review SLA | N/A | 100% First-Pass Approval | Production | Apple App Store & Google Play Store initial submission review records(2024) | Authored permission disclosures, Apple Sign-In implementation, and in-app purchase guidelines compliance. |
| Offline Workout Data Loss | 8.4% recorded failure rate | 0.0% reported lost workouts | Production | Production telemetry and sync reconciliation failure logs over 6-month period(2024 - 2025) | Engineered offline Hive transaction queue with idempotency keys. |
Evidence & Confidentiality Notice
Client details and production screenshots are omitted under confidentiality. The technical description has been generalized with client permission.
- The 60fps frame rate was validated on modern iOS devices and Android devices with Snapdragon 680 or higher; entry-level chipsets may experience brief frame drops during heavy background asset downloads.
- Reported 14ms API latency applies to warm cache Redis hits; cold uncached historical aggregations average 45-60ms.
Plan a Cross-Platform Mobile SaaS MVP
Looking to build a high-performance iOS and Android mobile app with a scalable Node.js backend?
Technology Stack & Tools Used
Need Similar Architecture or Development for Your Team?
AI Integration & RAG Development Services
Production-ready AI integrations, Retrieval-Augmented Generation (RAG) search, document intelligence, and secure LLM workflows for modern web apps and SaaS.
Custom Web Application & Website Development
High-performance custom web application and website development with Next.js 15, React, Node.js, and PostgreSQL for modern businesses.
Let's Build Your Custom Web Application
Whether you need a full-stack web app, a Node.js REST API, a Next.js SaaS MVP, an admin dashboard, or performance optimization for an existing application — I am available for freelance projects in Kerala, India, and worldwide.