Offline & Sync Architecture

Technical details on how EdCon operates offline on your school local area network (LAN) and automatically syncs with the cloud.

1. Hybrid Local-Cloud Design

EdCon's architecture is offline-first by design. The entire suite of application features (from attendance and assignment grading to student chats) is hosted on a local school server. Devices inside the school connect to this local server over the local Wi-Fi network or Ethernet LAN.

Local Operations: All queries, posts, messages, and grades are written instantly to the local server database (MongoDB), achieving microsecond response times and complete independence from external internet connections.
Cloud Replication: When an active external internet link is established on the local server, data syncs automatically to secure cloud repositories in the background, enabling parents and remote users to access grades and notifications.

2. Client-Side Service Worker

EdCon registers a robust, event-driven Service Worker (service-worker.js) on the student and teacher browsers. This guarantees application availability even if the local server momentarily drops offline.

Asset Caching

Static Asset Cache

The Service Worker caches structural HTML pages, stylesheets, images, and Javascript modules during the initial page load. Subsequent loads fetch directly from the device's cache, bypassing network requests completely.

Network Fallbacks

Request Interception & Offline Pages

If a network connection fails, the Service Worker intercepts the request and serves cached templates. If a page has not been cached, it renders the elegant offline fallback page (offline.html) prompting the user to check their LAN connection.

3. IndexedDB Sync Queue

To support offline transactions (such as writing chat messages, submitting files, or completing quizzes during network interruptions), EdCon utilizes an IndexedDB cache queue processor.

Queueing: Mutating actions (POST/PUT/DELETE requests) are intercepted when offline. The Sync Manager (sync-manager.js) serializes request payloads—including converting uploaded files and Blobs into storable ArrayBuffers—and writes them to the IndexedDB sync_queue store as pending items.
Auto-Reconciliation: The manager monitors browser online connectivity state. As soon as the network returns, the Sync Core (sync-core.js) processes the queue sequentially, submitting queued requests in chronological order.
Conflict Resolution: Timestamps are managed using client-supplied creation indicators, preventing out-of-order overrides and ensuring chronological accuracy.

4. Media CDN Fallback Protection

To optimize local server storage and protect against server hardware failures, EdCon integrates a background media synchronization protocol.

Ephemeral-Dyno Protection: File uploads (such as teacher attachments and profile pictures) are saved locally first. Background worker processes copy these assets asynchronously to Cloudinary CDN storage.
Redirect Fallback: If a local asset request cannot be fulfilled (for example, after a local server redeployment), the server intercepts the local path request and transparently redirects the browser to the CDN-backed replica.