How Instagram, WhatsApp, Uber & Netflix Would Be Built Today Using Expo Router

Janmejai Singh Posted on May 31           How Instagram, WhatsApp, Uber & Netflix Would Be Built Today Using Expo Router # reactnative # mobiledev # systemdesign # architecture You tap Record. You nail the take. You save as Draft. You close Instagram, reopen it — and your Reel is right there. What just happened under the hood? This post traces that full journey: from your device's camera buffer to your follower's screen halfway across the world. We'll cover local storage, drafts, cloud uploads, media processing, caching, and CDNs — with diagrams at each stage. Why Social Media Apps Need Efficient Media Storage Photos and videos are the heaviest assets any mobile app handles. A single 60-second Reel captured at 1080p can be 200–400MB before any compression. Multiply that by a billion daily uploads and you begin to understand why media storage is not a solved problem — it's an ongoing engineering discipline. Efficiency matters at three levels: Device level — local storage is limited; apps can't balloon in size Network level — large uploads over mobile connections are fragile and slow Cloud level — storing, processing, and serving billions of files requires distributed systems Instagram's architecture solves each of these with different tools, layered together. How Photos and Videos Are Stored Before Upload When you record a Reel, the app doesn't immediately try to upload it. Your device is the first storage layer. The recording pipeline looks like this: Camera Sensor ↓ In-Memory Frame Buffer ← (active recording, fast but volatile) ↓ Local Temp Cache ← (flushed from buffer, survives brief interruptions) ↓ User Decision Point ├── Discard → Delete temp files ├── Save Draft → Move to persistent storage └── Post → Enqueue for upload Enter fullscreen mode Exit fullscreen mode Why local-first? Three reasons: Networks are unreliable — especially on cellular. Streaming raw video directly to a cloud server mid-recording is a recipe for data loss. Us