1) Synchronous paths
Red flag: UI actions freeze >3s.
Likely cause: Heavy compute in HTTP request/response; unrealistic perf testing on empty data.
Action: Push non-trivial work to queues/streams; small validations only, guarded by strict timeouts + circuit breakers.
KPI: p95/p99 latency per endpoint; queue age; error budget burn.
2) Workload isolation
Red flag: User clicks stall ingestion; GUI becomes unresponsive under sensor spikes.
Likely cause: Shared workers/ASGs for frontend and ingestion.
Action: Separate pools, autoscaling, and queues for user traffic vs. device pipelines; isolate head-of-line risk.
KPI: Separate SLOs; saturation per pool; backlog depth.
3) Caching for responsiveness
Red flag: Repeated timeouts on read-heavy screens.
Likely cause: Recomputing hot aggregates on every request.
Action: In-memory/distributed cache (Redis/Memcached) with clear TTLs, invalidation, backfill, and stampede protection.
KPI: Cache hit rate; origin QPS; p95 end-to-end.
4) Command vs. telemetry vs. data
Red flag: Devices “fixed” only by power-cycling or shelling in.
Likely cause: One channel for everything; no ACK/QoS/retry semantics.
Action: Separate command/control, telemetry, and data channels; device shadow/state sync; explicit reliability.
KPI: Command success rate; time-to-recover; shadow drift rate.
5) Data serialization
Red flag: Bandwidth ceilings hit; partial or delayed payloads.
Likely cause: Verbose text formats used on constrained links.
Action: Use compact binary (ProtoBuf/FlatBuffers/CBOR) on device/internal links; reserve JSON for public APIs.
KPI: Bytes/event; CPU/parse cost; link utilization.
6) Network stack reuse
Red flag: Random crashes every 1–12 hours; ghost disconnects.
Likely cause: DIY TCP listeners treating streams like a message bus.
Action: Use proven brokers/gateways (MQTT/NATS/Kafka/CoAP servers); extend via plugins/handlers.
KPI: Broker uptime; reconnect rate; duplicate/partial msg rate.
7) Operational vs. analytical separation
Red flag: Live app slows or times out during analytics jobs.
Likely cause: One database for OLTP and OLAP.
Action: Keep transactional/time-series stores separate; stream/replicate into OLAP lakes/warehouses.
KPI: OLTP p95 under analytics load; replication lag; query slot utilization.
8) Failure capture \& forensics
Red flag: “We don’t know why it failed.”
Likely cause: Invalid/unparseable events dropped on the floor.
Action: DLQs with full payload + error metadata; rate-limit; protect sensitive data; trace IDs end-to-end.
KPI: DLQ volume; mean time to explain (MTTX); % issues closed with root cause.
9) Reuse without coupling
Red flag: Endless debates on “the right pattern,” refactors ripple across services.
Likely cause: Over-shared and modified libraries without versioned contracts.
Action: Versioned APIs/schemas; keep services independently deployable; minimize shared runtime code.
KPI: Independent deploy rate; breakage per release; contract test pass rate.