Realtime, WebSocket & Object Storage

8. Realtime & WebSocket

Current-state note (2026-08-18)

Today's realtime fan-out is in-process (tokio::broadcast), scoped to a single Stackhouse pod — there's no Redis PubSub cross-pod relay in the codebase yet. The Redis-PubSub design below is the proposed fix for running multiple pods at scale, not something already running.

WebSocket Architecture at Scale

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Key insight: Redis PubSub decouples pods. Any pod can receive a write, all clients on all pods get notified.

SSE vs WebSocket Routing

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Provider WebSocket Support

Feature	AWS	GCP	Hostinger	Hetzner	Heroku
WebSocket at LB	✅ ALB	✅	✅	✅	✅ (60s timeout ⚠️)
Sticky sessions	✅	✅	✅	✅	❌ (dyno routing)
Max WS connections	Unlimited	Unlimited	~10k	~10k	~25k
WS timeout (max)	No limit	No limit	60s ⚠️	No limit	55s ⚠️

⚠️ Heroku and some Hostinger plans have aggressive idle timeouts. Requires ping/pong every 50s.

9. Storage (File/Object)

Storage Architecture

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Upload flow: Client → Multipart POST /v1/storage/object/bucket/path → Validation (size, MIME, path) → Write to object storage backend → Update PostgreSQL metadata → Return { id, path, size, url }

Download flow: Client → GET /v1/storage/object/bucket/path → Check auth (public bucket = no auth required) → Serve file bytes with correct Content-Type, OR generate pre-signed URL (redirect to S3/GCS directly)

Image transforms (planned): On-demand resize via /object/bucket/img.jpg?w=200&h=200 → served from CDN after first transform → cached on disk (disk caching + CDN headers)

Object Storage Comparison

Feature	AWS S3	GCS	Cloudflare R2	MinIO (Hetzner)	Hostinger
S3-compatible API	✅	Partial	✅	✅	❌
Free egress	❌	❌	✅ (zero egress)	✅ (internal)	❌
Global CDN	CloudFront	Cloud CDN	✅ included	❌	❌
Storage cost/GB	$0.023	$0.020	$0.015	$0.004	~$0.01
Egress cost/GB	$0.09	$0.12	$0	$0 (internal)	~$0.05
Max object size	5TB	5TB	5TB	Unlimited	~5GB
Versioning	✅	✅	✅	✅	❌
Lifecycle policies	✅	✅	✅	✅	❌