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Transmission of signals from Askmebet server to players
This document describes how real time signals (game state updates, bet confirmations, odds changes, notifications) should be transmitted from Askmebet servers to players. It covers architecture, protocols, message design, reliability, security, scaling, monitoring, and testing — enough to guide engineers building a robust, low latency delivery layer.
Goals
• Deliver timely, ordered, and authenticated events to connected players.
• Minimize latency and jitter for interactive flows (in play betting, live games).
• Ensure correctness (no lost or duplicated critical events like payouts).
• Scale horizontally to tens/hundreds of thousands of concurrent connections.
• Secure channels from tampering and protect PII.
Architecture overview
• Edge layer: global load balancers + TLS terminators (CDN or cloud LB).
• Connection gateway: fleet of stateless real time gateways (WebSocket/WebRTC/SSE) handling client sessions. Gateways forward events to/from backend services using a fast pub/sub bus.
• Backend services: game engine, matching/payment service, offers/odds engine publish canonical events to the pub/sub.
• Pub/sub / streaming bus: durable, low latency broker (e.g., Kafka, Pulsar, Redis Streams, or managed pub/sub) for event distribution and replay.
• State & persistence: authoritative transaction DB and write ahead logs (for PITR), optionally a transactional event store for critical flows.
• Replay & recovery: gateway can request missed events from the bus or an event store during reconnect.
Protocols & transport
Choose based on latency, NAT traversal, and client capabilities:
• WebSocket (preferred): full duplex, low overhead, works across browsers and mobile apps. Use for most live flows and two way communication.
• WebRTC DataChannels: for ultra low latency P2P or when media is combined with data (live streaming + game signals). More complex to scale.
• Server Sent Events (SSE): simple uni directional stream; easier for read only updates but less flexible.
• Long polling (fallback): for legacy clients or in restrictive networks.
Use TLS (WSS/WSSecure) always. Keep payloads compact (binary protobuf/msgpack preferred) and versioned.
Message design
• Schema: small, explicit schemas (e.g., Protocol Buffers, FlatBuffers) for compactness and forward/backward compatibility.
• Envelope fields: {message_id, type, timestamp_utc, seq_no, player_id/session_id, correlation_id, payload_version, signature_hash (optional)}.
• Idempotency: include unique message_id and seq_no to allow clients to detect duplicates and apply ordering.
• Types: state_delta (small diffs), snapshot (full state), ack, command_response, heartbeat.
• Compression: apply per message compression for larger payloads; avoid compressing tiny messages.
Ordering & reliability
• Per session sequencing: gateways enforce monotonic seq_no per session. For multi device same account, use per session sequences and server side reconciliation.
• Critical events: require server ACK and durable persistence. On disconnect/reconnect, client requests last seen message_id to replay missed critical events.
• Exactly once vs at least once: aim for idempotent handlers and at least once delivery with message_id dedupe at client and server for financial-critical flows.
• Heartbeats: short interval heartbeats (e.g., 10–30s) to detect broken connections and measure latency.
Scaling & resilience
• Horizontal gateway autoscaling behind LB; sticky session support where needed or stateless session registry (session metadata in Redis).
• Partition pub/sub by logical keys (player_id, game_id) to localize traffic and reduce fan out.
• Fan out strategies: single multicast topic for high volume broadcasts (odds updates) with gateway side filtering; or partitioned topics per region/game.
• Backpressure: gateways advertise buffer status; publishers slow down or aggregate when gateways are congested. Use rate limits and circuit breakers.
• Failover: multi AZ/multi region replication of pub/sub and persistent stores; graceful reconnect strategies with exponential backoff and jitter.
Security & compliance
• Mutual authentication: JWT short lived tokens or mTLS for sensitive clients. Tokens tied to session and scope (read/write).
• Encryption: TLS 1.2+ for transit; encrypt sensitive payload fields at rest.
• Authorization: server checks per message ACLs; disallow cross account message visibility.
• Audit logging: log all financial/significant events (deliveries, acks, replays) to an append only audit store.
• Rate limiting & fraud detection: detect abnormal message patterns and throttle/suspend sessions.
Monitoring & observability
• Metrics: connection count, open/close rates, avg RTT, message latency distribution (p50/p95/p99), publish/consume lag, error rates, retransmit counts.
• Tracing: inject trace IDs into messages for distributed tracing of end to end flows (client → gateway → backend).
• Logs: structured logs for session lifecycle, reconnects, message acks; retain per compliance needs.
• Alerting: SLO breaches (latency, error rate), abnormal disconnect spikes, pub/sub lag thresholds.
Testing & validation
• Load tests simulating realistic mixes: many small messages, bursts, and long idle sessions.
• Chaos & failure injection: simulate gateway restarts, pub/sub broker failover, network partitions.
• Integration tests: validate replay correctness, idempotency, ordering under churn.
• Synthetic monitoring: regular end to end probes from multiple regions mimicking client behavior.
Example flow (bet placement)
1. Client sends bet request over WebSocket to gateway.
2. Gateway forwards to payments/matching service (synchronously or via request bus).
3. Backend persists transaction, publishes event "bet_confirmed:{id}" to pub/sub.
4. Gateway subscribed to player's topic receives event, sends "bet_confirmed" message with seq_no and message_id to client.
5. Client ACKs message_id; gateway logs delivery. If client missed it (reconnect), client requests last_seen_id to replay.
Best practices summary
• Use compact binary messaging, TLS, and short token lifetimes.
• Keep critical events durable and replayable; prefer idempotent processing.
• Partition and localize pub/sub to reduce cross traffic and latency.
• Monitor end to end latency, implement backpressure, and perform regular restore/replay drills.
• Treat financial and PII signals with stronger audit, encryption, and provenance guarantees.