My Financial Trading

Token-based auth added a MongoDB lookup on every request, which became a bottleneck under concurrent load.

Cache token validity in Redis with a 3-hour TTL keyed by a hash of the raw token. Invalidation happens implicitly when the token changes on logout.

A revoked token remains valid in cache for up to 3 hours unless the key expires or the Redis entry is explicitly deleted. Accepted because refresh-token rotation is the primary logout mechanism.

Video files needed to be access-controlled without exposing the storage URL, while still supporting HTTP range requests for seeking.

Generate a short-lived JWT per video access. The streaming endpoint verifies the token server-side, performs the range request against S3, and proxies the binary stream back to the client.

All video traffic passes through the Node.js process, increasing memory and CPU load. Chosen over signed S3 URLs because it allows per-browser response header control and centralised access revocation.

Video compression and thumbnail generation are CPU-heavy and would block the event loop if run inline in a request handler.

Upload triggers a BullMQ job. The worker calls FFmpeg via fluent-ffmpeg for compression and Sharp for thumbnail generation, uploads the result to S3, then saves the URL to MongoDB.

Adds latency between file upload and content availability. Stream-video-processing concurrency is set to 1 to avoid exhausting CPU on a constrained deployment.

Safari and iOS clients require different Cache-Control and Connection header semantics for HTTP range requests to function correctly during video playback.

The streaming service detects the browser from the User-Agent header and applies browser-specific response headers: no-cache + keep-alive for Chrome, public max-age=3600 for Safari/iOS, broader stale-while-revalidate for others.

A single streaming endpoint handles all browser targets without client-side changes.

Scheduled newsletters could be silently missed if the server restarted between the scheduling cron tick and the delivery time.

A recovery loop inside the 5-minute cron looks back 24 hours for newsletters that are unsent and not in the queue. It re-enqueues them with a 5-second delay and marks them as scheduled in the DB before adding to the queue to prevent duplicates.

Missed newsletters are detected and re-queued on the next cron tick with no manual intervention required.

Three payment gateways (Stripe, Apple StoreKit, CoinPayments) each have different webhook formats, verification requirements, and subscription event lifecycles that needed to converge on the same data model.

Each gateway has its own verification helper (Stripe HMAC on raw body, Apple receipt verification via Apple's endpoint, CoinPayments HMAC signature). All three update the same Payment and Student Prisma models and normalise to a shared PaymentStatus enum.

Subscription state is consistent across gateways; the rest of the application only reads PaymentStatus without knowing which gateway was used.