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E5: Waiting Queue System

Overview

Bounded Context / Service: Queue Service, Mobile App

Goal: Manage high-demand match ticket sales with fair queuing for 100k+ concurrent users.

Priority: High

Primary User Roles

  • Fan

Scope

In-Scope

  • Queue join and position assignment
  • Real-time position updates (client countdown + server sync)
  • Progressive push notifications (position change, near position, your turn)
  • 20-minute purchase window enforcement
  • Connection resilience (30-minute position persistence)
  • Multi-device synchronization (same user = same position)
  • Continue shopping while in queue
  • Queue closure when sold out

Out-of-Scope

  • Priority queue for VIPs (use quota instead)
  • Queue bypass mechanisms

Features

ID Feature Size Description
E5-F1 Queue Join and Position Assignment M Join queue and get position
E5-F2 Real-Time Position Updates M WebSocket/Firebase updates
E5-F3 Queue Progressive Notifications S Push at key milestones
E5-F4 Purchase Window Enforcement S 20-minute window at front
E5-F5 Queue Connection Resilience S 30-minute position persistence

Dependencies

  • Redis Cluster for queue data structures
  • Firebase Cloud Messaging for push notifications
  • WebSocket or Firebase for real-time updates

Technical Architecture

Queue Service Extraction

The Queue System is extracted as a standalone auto-scaling microservice separate from the main Symfony monolith. It activates automatically based on traffic demand (e.g., traffic spikes during high-demand sales) — there is no per-match toggle. Implementation details TBD.

Why Extract as Separate Service

Requirement Challenge in PHP/Symfony Solution
100k+ concurrent connections PHP not optimized for long-lived WebSocket connections Node.js or Go runtime
Real-time position updates Blocking I/O impacts other modules Dedicated service with event loop
Independent scaling Queue traffic 10x higher than checkout Horizontal pod scaling
Blast-radius isolation Queue surges risk degrading checkout Separate deployment

Queue Service Responsibilities

  • Queue join and FIFO position assignment (Redis sorted set)
  • Real-time position updates via WebSocket/SSE
  • 20-minute purchase window enforcement
  • 30-minute position persistence on disconnect
  • Sold-out detection and queue closure

Communication with Monolith

Mobile App ──WebSocket──► Queue Service ──Redis Pub/Sub──► Monolith (E4)
                                │
                                ▼
                         Redis Cluster
                    (sorted sets, pub/sub)
Direction Protocol Events
App → Queue Service WebSocket Join, heartbeat, disconnect
Queue Service → App WebSocket Position updates, turn granted
Queue Service → Monolith Redis Pub/Sub queue.turn_granted, queue.expired
Monolith → Queue Service REST /queue/{match_id}/sold-out

See Microservices Strategy for detailed API contracts.

Risks & Open Questions

OQ-E5-1: Queue Throughput

What is the expected queue throughput rate (users processed per minute)?

OQ-E5-2: Bot Detection

What bot detection and prevention mechanisms are required?

Risk: Redis Sizing

Redis cluster sizing for 100k+ concurrent users requires careful planning and load testing.

Last Updated: January 2026