7 — Cloudflare Edge Platform
Rank 15 of 28 · Tier B · app/workers/, app/GlobalCloudflareAdapter, app/BillboardGateway/worker
Stack: TypeScript, Hono, Cloudflare Workers, D1, R2, KV, Durable Objects, Hyperdrive, WASM, Cloudflare Stream, wrangler
Why this ranks here. Edge compute is genuinely differentiated experience — and the constraints are what make it interesting to a distributed-systems interviewer. No TCP sockets, no long-lived state, single-writer Durable Objects, and a cold-start budget. Every one of those forced a real architectural decision here.
The fleet
| Worker | Role |
|---|---|
billboard_users |
10.5K lines, 65 routes — library, playlists, feed, charts, Jamz matching |
billboard-feed-worker |
Feed API (was mock-only; identified and replaced) |
global_upload_service |
Media ingest, R2 multipart, IngestDO |
boxoffice-api |
Video catalog and moderation queue |
global_search |
Cross-mode search |
explore |
Discovery surfaces |
match_service |
Edge-side match endpoints |
storefront |
Commerce |
rpc_worker |
Service-to-service RPC |
array-media-service-manager-v2 |
Media orchestration |
Plus billboard-gateway-edge — R2 range streaming for audio, with an
/api/* proxy to the Node origin.
The interesting constraint
Workers cannot open raw TCP sockets. Not with a library, not with a shim. That makes the Kafka wire protocol and CQL permanently unreachable from the edge.
This is the constraint that produced the Activity Graph's outbox design: the Worker writes an event row transactionally, and a separate host-resident Go process relays it into Kafka. The architecture is a direct consequence of a platform limit, which is exactly the reasoning shape a systems-design interview is looking for.
Storage primitives, and what each is for
| Primitive | Used for | Why not the others |
|---|---|---|
| D1 (SQLite) | Relational user/library data | Cheap, transactional, edge-local reads |
| R2 | Audio/video objects, multipart ingest | No egress fees; range requests for streaming |
| KV | Config, hot lookups | Eventually consistent, so never for anything ordered |
| Durable Objects | Upload sessions (IngestDO), fingerprinting (JamzFingerprintDO) |
Single-writer coordination — the only strong-consistency tool at the edge |
| Hyperdrive | Pooled Postgres from the edge | Connection pooling that Workers otherwise cannot have |
WASM at the edge
JamzFingerprintDO loads kissfft.wasm — an FFT compiled to WebAssembly
to compute audio fingerprint constellations inside a Durable Object. (The
module was referenced but had never been built; building it was commit
e04aaf6fb.) The emsdk/ and chromaprint/ trees in /srv are the
toolchain and reference implementation behind it.
Scope
| Metric | Value |
|---|---|
| Workers | 10 |
| Edge TypeScript | ~75K lines |
| Storage primitives | D1, R2, KV, Durable Objects, Hyperdrive |
| Notable | WASM FFT in a DO; R2 range streaming; multipart ingest |
Interview surface this opens
- Durable Objects as a distributed single-writer primitive vs Raft/leases
- Eventual consistency in KV and why ordered data never belongs there
- Edge-to-origin patterns when the edge cannot speak your protocol
- Connection pooling for serverless (Hyperdrive) and the pool-exhaustion problem
- Range requests and byte-range streaming for media