Debug This Architecture

Here’s a comprehensive analysis of potential failure modes, race conditions, and scaling bottlenecks in your architecture, along with proposed solutions and trade-offs:

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1. WebSocket Connection Fragmentation

Problem: Clients connected to different API servers won’t receive real-time updates from each other due to isolated WebSocket connections per server. Polling PostgreSQL every 2 seconds introduces latency (up to 2s sync delay).
Solution:

• Use a Pub/Sub system (e.g., Redis Pub/Sub or Kafka) to broadcast changes across all servers.
  • Trade-off: Adds complexity but ensures near-instant cross-server sync (~ms latency).
• Sticky sessions (via load balancer) to group users editing the same document on the same server.
  • Trade-off: Reduces fragmentation but hurts load balancing fairness.

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2. Last-Write-Wins (LWW) with Client Clocks

Problem: Client clocks are unreliable (can drift or be maliciously set), leading to data loss if a stale edit has a later timestamp.
Solution:

• Server-assigned timestamps (monotonic logic clocks or hybrid logical clocks).
  • Trade-off: Adds server dependency for ordering but prevents conflicts.
• Operational Transformation (OT) or CRDTs for conflict-free merging.
  • Trade-off: Complex implementation but preserves all edits.

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3. PostgreSQL Polling Bottleneck

Problem: Polling every 2s scales poorly (N servers × M documents → high DB load).
Solution:

• PostgreSQL LISTEN/NOTIFY for change events.
  • Trade-off: Lower latency but requires DB connections to stay open.
• Debounce polling (e.g., only poll documents with active edits).
  • Trade-off: Reduces load but may miss rapid sequential edits.

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4. Full HTML Snapshots Every 30s

Problem: Storage bloat (especially for large documents) and expensive snapshotting under high load.
Solution:

• Delta-based storage (store only changes + periodic snapshots).
  • Trade-off: More complex recovery but saves space.
• Compress snapshots (e.g., gzipped HTML).
  • Trade-off: CPU overhead for compression.

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5. JWT in localStorage XSS Risk

Problem: Storing JWTs in localStorage makes them vulnerable to XSS attacks.
Solution:

• Use httpOnly cookies for JWTs.
  • Trade-off: Harder to implement with WebSockets (requires CSRF protection).
• Short-lived JWTs (5–10 min) + refresh tokens.
  • Trade-off: More auth requests but reduces exposure.

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6. API Response Caching (5 min)

Problem: Stale document data if cached API responses don’t reflect real-time edits.
Solution:

• Cache busting per document (invalidate cache on edit).
  • Trade-off: Higher CDN load but ensures freshness.
• Edge-side includes (ESI) for dynamic parts.
  • Trade-off: Complex CDN configuration.

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7. Scaling PostgreSQL Writes

Problem: High write load during peak editing (all changes hit the primary DB).
Solution:

• Shard documents by organization ID (as planned) + use connection pooling.
  • Trade-off: Sharding complicates queries.
• Write-ahead logging (WAL) + async replicas for eventual consistency.
  • Trade-off: Risk of stale reads.

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8. WebSocket Server Overload

Problem: A single server handling too many WebSocket connections (memory/CPU limits).
Solution:

• Dedicated WebSocket servers (separate from API servers).
  • Trade-off: Higher infrastructure cost.
• Limit connections per server (e.g., 10k/server).
  • Trade-off: More servers needed.

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9. No Graceful Degradation

Problem: If WebSockets fail, the UI may freeze (no fallback).
Solution:

• Long-polling fallback when WebSockets disconnect.
  • Trade-off: Higher latency but resilient.

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10. Document Partitioning by Org ID

Problem: Hot partitions if some orgs are much more active.
Solution:

• Dynamic partitioning (e.g., split large orgs into sub-partitions).
  • Trade-off: Requires runtime rebalancing.

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11. Redis Cache Failover

Problem: Session cache loss if Redis fails.
Solution:

• Redis Cluster (with replicas) + local cache fallback.
  • Trade-off: Higher Redis costs.

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Summary of Key Fixes:

1. Replace polling with Redis Pub/Sub or LISTEN/NOTIFY.
2. Use server timestamps or CRDTs instead of client clocks.
3. Delta storage + compression for snapshots.
4. Shard PostgreSQL + optimize writes.
5. Secure JWTs with httpOnly cookies or short expiry.

Each solution balances performance, complexity, and reliability. The highest-priority fixes are WebSocket fragmentation (Pub/Sub) and LWW conflicts (server timestamps).