14 — Monitoring and Observability

flowchart TB
    Obs["Observability"] --> Logs["📝 Logs<br/>Events that happened<br/>'User 123 placed order'"]
    Obs --> Metrics["📊 Metrics<br/>Aggregated measurements<br/>'500 requests/sec, 95% latency: 150ms'"]
    Obs --> Traces["🔍 Traces<br/>Request lifecycle<br/>'Order took 2.3s across 4 services'"]

    Logs --> LogTools["ELK Stack, Loki, CloudWatch Logs"]
    Metrics --> MetricTools["Prometheus, Grafana, Datadog"]
    Traces --> TraceTools["Jaeger, Zipkin, X-Ray"]

    style Obs fill:#7c3aed,color:#fff
    style Logs fill:#3b82f6,color:#fff
    style Metrics fill:#059669,color:#fff
    style Traces fill:#f59e0b,color:#fff

flowchart LR
    SLI["SLI — Service Level Indicator<br/>(What we measure)<br/>Latency: P99 < 200ms"] --> SLO["SLO — Service Level Objective<br/>(Our target)<br/>99.9% of requests < 200ms"]
    SLO --> SLA["SLA — Service Level Agreement<br/>(Contract with users)<br/>99.9% uptime, or refund"]

    style SLI fill:#3b82f6,color:#fff
    style SLO fill:#059669,color:#fff
    style SLA fill:#ef4444,color:#fff

flowchart TB
    subgraph Sources["Data Sources"]
        App["Application Logs"]
        Infra["Infrastructure Metrics<br/>CPU, RAM, Disk"]
        DB["Database Metrics"]
        LB["Load Balancer Metrics"]
    end

    subgraph Collection["Collection & Storage"]
        Agent["Agents / Exporters"]
        TSDB["Time Series DB<br/>Prometheus / InfluxDB"]
        LogDB["Log Storage<br/>Elasticsearch / Loki"]
        TraceDB["Trace Storage<br/>Jaeger / Tempo"]
    end

    subgraph Visualization["Visualization & Alerting"]
        Grafana["Grafana Dashboards"]
        Alert["Alert Manager<br/>PagerDuty, Slack"]
    end

    Sources --> Collection
    Collection --> Visualization

    style Sources fill:#3b82f6,color:#fff
    style Collection fill:#7c3aed,color:#fff
    style Visualization fill:#059669,color:#fff

sequenceDiagram
    participant Client as Client
    participant GW as API Gateway
    participant Auth as Auth Service
    participant Order as Order Service
    participant DB as Database

    Note over Client,DB: Trace ID: abc-123 (passed via headers)

    Client->>GW: POST /orders
    GW->>Auth: Validate token (trace: abc-123)
    Auth-->>GW: Valid (5ms)
    GW->>Order: Create order (trace: abc-123)
    Order->>DB: INSERT order (trace: abc-123)
    DB-->>Order: OK (20ms)
    Order->>DB: INSERT order_items (trace: abc-123)
    DB-->>Order: OK (15ms)
    Order->>Order: Calculate total (trace: abc-123)
    Order-->>GW: Order created (50ms total)
    GW-->>Client: 201 Created (65ms total)