| # | Component | Layer | One-Line |
|---|---|---|---|
| IC1 | DNS | Request | Maps hostnames to IPs; first lookup for every request |
| IC2 | CDN | Request | Caches content at edge; reduces origin load and latency |
| IC3 | Load Balancer | Request | Distributes traffic across instances; removes unhealthy ones |
| IC4 | API Gateway | Request | Single external entry point; auth, rate limiting, routing |
| IC5 | Service Mesh | Request | Service-to-service mTLS, retries, circuit breaking via sidecars |
| IC6 | Rate Limiter | Request | Caps request rate per client or endpoint |
| IC7 | App Server | Application | Stateless compute layer; executes business logic |
| IC8 | Background Worker | Application | Async task execution; decouples creation from execution |
| IC9 | Cache Server | Application | In-memory key-value; microsecond reads for hot data |
| IC10 | Sync RPC/REST | Communication | Synchronous service-to-service calls |
| IC11 | Service Discovery | Communication | Dynamic registry of where services are running |
| IC12 | Relational DB | Storage | ACID transactions; structured data with a schema |
| IC13 | Message Queue | Storage | Durable async messaging; decouples producers and consumers |
| IC14 | NoSQL Document | Storage | Flexible schema; horizontal write scale |
| IC15 | Key-Value Store | Storage | O(1) lookup by key; sessions, config, cache |
| IC16 | Wide-Column Store | Storage | Write-heavy time-series and activity data |
| IC17 | Object Storage | Storage | Durable binary blob storage; images, video, backups |
| IC18 | Search Index | Storage | Full-text and faceted retrieval |
| IC19 | Vector Database | Storage | Similarity search for ML embeddings |
| IC20 | Batch Processor | Processing | Scheduled large-scale data transformation jobs |
| IC21 | Stream Processor | Processing | Continuous real-time event processing |
| IC22 | Metrics System | Observability | Time-series counters and gauges; alerting |
| IC23 | Log Aggregator | Observability | Centralised structured log storage and query |
| IC24 | Distributed Tracing | Observability | Request-latency attribution across service hops |
| IC25 | Config Management | Control | Centralised runtime configuration and feature flags |
| IC26 | Orchestrator | Control | Schedules and supervises compute workloads |
Use: For any system design, identify which of the 26 are present. A missing component that should be there is a gap in the design.