Technical Architecture

System Overview

Eli is built as a modern, cloud-native SaaS platform designed for global enterprise deployment. Our architecture prioritizes security, scalability, and compliance while maintaining high availability across multiple geographic regions.

System Architecture Diagram

Note: This diagram provides a simplified view of Eli's core architecture and its purpose is not to display all of its sub-processors. For a complete list of sub-processors and third-party services we work with, please refer to our Who We Work With page.

Application Architecture

Application layer

Admin app (Front only) - app.eliapp.io

• Purpose: Campaign management interface for organizational administrators, HR teams, and communication managers
• Technology: Next.js 15.2, React 19, TypeScript, Tailwind CSS
• Platform: Any browser, ES2022
• Key Features: Campaign creation, analytics dashboard, user management, content authoring
• Authentication: Multi-method support through Eli Authentication Service
• API Integration: Consumes Admin API

Employee app (Front only) - my.eliapp.io

• Purpose: Employee engagement platform for campaign participation, content consumption and employee interaction
• Technology: Next.js 15.2, React 19, TypeScript, Tailwind CSS
• Platform: Any browser, ES2022
• Key Features: Campaign participation, progress tracking, interactive challenges, online communities
• Authentication: Multi-method support through Eli Authentication Service
• API Integration: Consumes User API

Mobile app - m.eliapp.io

• Purpose: Employee engagement platform for campaign participation and content consumption and employee interaction
• Technology: Flutter framework for cross-platform deployment
• Platforms: Native iOS and Android applications
• Key Features: Campaign participation, progress tracking, enhanced interactive challenges, online communities, offline capabilities, push notifications, deep linking
• Authentication: Multi-method support through Eli Authentication Service
• API Integration: Consumes User API

Auth app (Full-stack) - auth.eliapp.io

• Purpose: Centralized authentication and session management for other Eli apps
• Technology: Next.js 15.2, React 19, Firebase Auth integration
• Features: SSO support, session management, security token generation
• Integration: Validates all requests across the platform ecosystem
• Authentication methods:
  • Sign in With Google
  • Sign in With Apple
  • Email / password
  • OTP via email

API app (Back only) - api.eliapp.io

• Framework: Express.js with Node.js runtime
• API Design: tRPC (Type-safe Remote Procedure Calls) for end-to-end type safety
• Architecture: Microservices pattern with three dedicated API endpoints:
  • User API (/trpc/user): Employee-facing features and mobile app support. Cookie-based auth.
  • Admin API (/trpc/admin): Administrative functions and campaign management. Cookie-based auth.
  • Service API (/trpc/service): External integrations, webhooks, and system callbacks. 164-chars Bearer tokens auth.

Data layer

Our database: MongoDB Atlas

• Configuration: 3-replica set for high availability and data redundancy
• Location: Google Cloud Platform, Belgium region (europe-west1)
• Features: Automatic failover, point-in-time recovery, encryption at rest
• ORM: Prisma for type-safe database access and schema management. Prisma schemas (and API schemas) are shared to all apps through internal packages for bullet-proof consistency and safety.

Our file storage: Firebase storage

• Location: Belgium (europe-west1)
• Use Cases: User profile pictures, images shared in posts,...

Infrastructure & Hosting

Our primary hosting platform: Vercel

• Location: Paris, France (AWS eu-west-3 region)
• Features:
  • Global CDN with edge computing capabilities
  • Automatic scaling based on traffic demand
  • Built-in DDoS protection and security filtering
  • Zero-downtime deployments

Our queue management system: Upstash Qstash

• Use Cases: Email sending, Push Notifications, background processing, scheduled tasks
• Features: Automatic retries, dead letter queues, monitoring and observability

Our email delivery system: Resend

• Location: Ireland (AWS eu-west-1 region)
• Use Cases: Transactional emails, campaign notifications, OTP delivery, system alerts
• Features: High deliverability rates, webhook support, email analytics, API-first design

Scalability & Performance

Auto-scaling capabilities

• Application layer: Automatic horizontal scaling on Vercel based on traffic demand
• Database: MongoDB Atlas auto-scaling with performance optimization
• Queue system: Distributed processing with automatic retry mechanisms
• CDN: Global edge locations for optimal content delivery all around the globe

Data Residency & EU compliance at a glance

• Web Services: Hosted in Paris, France (AWS eu-west-3 CDG1)
• Database: Hosted in Belgium (GCP europe-west1)
• Compliance: GDPR-compliant by design with EU data residency
• Security: All communications over HTTPS/TLS 1.3 encryption

Development & Deployment

Version control

We use Gitlab for all our projects.

Continuous Integration & Deployment

Web apps (all of them)

• Vercel CI pipeline for build automation and deployment
• Zero-warning linting policy at high standards
• Staging environments and rollback capabilities

Android app

• Gitlab CI pipeline for build automation and Play Store deployment
• Zero-warning linting policy
• Staging environments and rollback capabilities

iOS app

• Gitlab CI pipeline for build automation and App Store deployment
• Zero-warning linting policy
• Staging environments and rollback capabilities

Technology Stack Summary

Frontend & mobile: Next.js 15.2, React 19, TypeScript, Tailwind CSS, Flutter
Backend: Node.js, Express.js, tRPC, Prisma ORM
Database: MongoDB Atlas (3-replica set)
Authentication: Firebase Auth
Storage: Firebase Storage
Queue: Upstash QStash
Email: Resend
Hosting: Vercel (Paris), GCP (Belgium)
CI/CD: Vercel, GitLab CI, XCode Cloud

---

For technical architecture questions, contact: security@eli.app

Last Updated: August 2025