ResilientSync

ResilientSync is an offline-first synchronization framework for applications that need to keep working even when internet is not available.

The main idea is simple: different devices should be able to work independently, save their changes locally, and when connection comes back, all the changes should sync and merge safely without losing data.

I used a healthcare / field worker example in the demo because it makes the problem easy to understand, but the framework itself is generic and can be used in other kinds of apps too.

---

What problem this solves

In many real situations, internet is unstable or fully unavailable.

Examples:

• disaster zones
• rural healthcare
• field surveys
• remote research work

If two devices both update the same record while offline, most normal systems either:

• overwrite one version
• lose data
• or ask the user to manually fix the conflict

This project tries to solve that by:

• storing operations locally
• syncing later
• resolving conflicts automatically

---

Main features

• offline-first local storage
• operation-based synchronization
• automatic sync when online
• Last-Write-Wins conflict resolution
• Tombstone deletion handling
• G-Counter support for grow-only counters
• duplicate detection using UUID operation IDs
• dead letter queue for rejected operations
• validation of incoming operations
• web UI for field worker + dashboard + DLQ view
• unit tests and integration tests

---

Tech used

• Node.js
• Express.js
• SQLite
• JavaScript
• HTML / CSS
• UUID
• CORS

---

Project structure

resilient-sync/
├── src/
│   ├── core/
│   ├── strategies/
│   ├── adapters/
│   ├── shared/
│   └── index.js
│
├── server/
│   └── index.js
│
├── demo/
│   ├── app/                  # new combined web UI
│   ├── healthcare/           # old CLI demo files + scenario
│   └── dashboard.js          # old dashboard backup
│
├── test/
│   ├── unit/
│   └── integration/
│
├── docs/
├── package.json
└── README.md