Failure Modes, Race Conditions, and Scaling Bottlenecks Analysis

1. WebSocket Connection Management

Issue: WebSocket connections are server-specific, causing connection loss during server failover or scaling events.

Solution: Implement a connection pool with automatic reconnection logic in the client. Use a consistent hashing load balancer that preserves affinity during scaling.

Trade-offs:

• Pro: Seamless user experience during minor server events
• Con: Increased client complexity, potential for duplicate connections during rapid scale events

2. Last-Write-Wins Conflict Resolution

Issue: Client clocks can be out of sync, leading to incorrect conflict resolution where earlier edits overwrite newer ones.

Solution: Implement vector clocks or version vectors instead of simple timestamps. Track edit history and allow manual conflict resolution when detected.

Trade-offs:

• Pro: More accurate conflict resolution, preserves edit history
• Con: Increased complexity in storage and comparison logic, slightly higher network overhead

3. Polling-Based Sync Between Servers

Issue: 2-second polling creates unnecessary database load and potential for stale data between servers.

Solution: Replace polling with a publish-subscribe system (like Redis Pub/Sub) for real-time change propagation between servers.

Trade-offs:

• Pro: Near real-time sync between servers, reduced database load
• Con: Adds dependency on Redis Pub/Sub, potential for message loss if Redis fails

4. Document Partitioning

Issue: Partitioning by organization ID may lead to hot partitions for large organizations.

Solution: Implement sharding at the document level rather than organization level, with a consistent hashing ring for distribution.

Trade-offs:

• Pro: Better load distribution, prevents hot partitions
• Con: More complex sharding logic, potential for cross-shard queries

5. JWT Token Expiry

Issue: 24-hour expiry and localStorage storage creates poor UX for long sessions and security risks if device is compromised.

Solution: Implement refresh tokens with shorter-lived JWTs. Store refresh tokens in HttpOnly cookies with secure flags.

Trade-offs:

• Pro: Better security, smoother session renewal
• Con: Increased server load for token validation, more complex token management

6. HTML Snapshot Storage

Issue: Storing full HTML snapshots every 30 seconds is inefficient and creates storage bloat.

Solution: Implement operational transformation or differential synchronization to store only changes between versions.

Trade-offs:

• Pro: Reduced storage needs, faster sync times
• Con: Increased complexity in the sync algorithm, potential for sync drift over time

7. CDN Caching API Responses

Issue: Caching API responses for 5 minutes conflicts with real-time document updates.

Solution: Don't cache document-related API responses. Only cache static assets and user-specific responses with appropriate cache headers.

Trade-offs:

• Pro: Ensures real-time updates are always current
• Con: Reduced CDN benefits for dynamic content, potentially higher origin server load

8. Database Write Contention

Issue: Multiple servers writing to the same document rows creates lock contention.

Solution: Implement optimistic locking with version numbers or implement a write coordinator pattern for document updates.

Trade-offs:

• Pro: Reduces database contention, better concurrency
• Con: Increased complexity in update logic, potential for more retries

9. Session Cache in Redis

Issue: Single point of failure for session data if Redis goes down.

Solution: Implement Redis clustering with replication, and add a fallback to database lookup for sessions if Redis is unavailable.

Trade-offs:

• Pro: High availability for session data
• Con: Increased complexity, potential for temporary performance degradation during failover

10. Load Balancer Affinity

Issue: Round-robin load balancing breaks WebSocket affinity when servers are added/removed.

Solution: Use a consistent hashing load balancer that maintains session affinity even as the server pool changes.

Trade-offs:

• Pro: Maintains WebSocket connections during scaling events
• Con: Less even distribution of connections during scaling, potential for some servers to be overloaded

11. Clock Skew Between Clients

Issue: Client clocks can be significantly out of sync, affecting conflict resolution.

Solution: Implement server-side timestamping for all operations, and adjust client clocks using NTP synchronization.

Trade-offs:

• Pro: More accurate conflict resolution, consistent view of edit history
• Con: Increased server load for timestamping, potential for slight delays in user feedback

12. Document Version History

Issue: No mechanism to revert to previous versions or track edit history.

Solution: Implement a version control system for documents with regular snapshots and delta storage.

Trade-offs:

• Pro: Better audit trail, ability to revert changes
• Con: Increased storage needs, more complex document management

13. Network Partitions

Issue: Network partitions can cause some servers to be isolated, leading to inconsistent state.

Solution: Implement a quorum-based system for document updates and use consensus protocols for critical operations.

Trade-offs:

• Pro: Better consistency during network issues
• Con: Increased latency for updates, more complex failure detection

14. Memory Usage for WebSocket Connections

Issue: Each server maintains its own WebSocket connections, which can consume significant memory at scale.

Solution: Implement a dedicated WebSocket service that can scale independently, using a message broker to route updates.

Trade-offs:

• Pro: Better resource utilization, dedicated scaling for real-time features
• Con: Increased system complexity, additional service to manage

15. Initial Document Load

Issue: Loading full document history on initial connect can be slow for large documents.

Solution: Implement incremental loading with virtual scrolling, loading only visible portions initially.

Trade-offs:

• Pro: Faster initial load time, better perceived performance
• Con: More complex client rendering logic, potential for layout shifts

These solutions address the major failure modes, race conditions, and scaling bottlenecks while considering the trade-offs between complexity, performance, and reliability. The specific implementation would depend on the exact requirements and constraints of the system.