> For the complete documentation index, see [llms.txt](https://docs.eliapp.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.eliapp.io/confidentialite-et-securite-en/service-overview/how-its-built.md). # How it's built ### 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](/confidentialite-et-securite-en/service-overview/who-we-work-with.md) 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](mailto:security@eliapp.io) **Last Updated:** October 2025