Architecture

graph TB
    %% Client
    subgraph ClientLayer["Client Layer"]
        Client[HTTP Client]
    end

    %% Application
    subgraph AppLayer["Application Layer"]
        App[items-service]
        ItemsEndpoint[/items endpoint/]
        MetricsEndpoint[/metrics endpoint/]
        OTel[OpenTelemetry SDK]
        Logs[Application Logs]
    end

    %% Observability
    subgraph ObsLayer["Observability Stack"]
        Prometheus[Prometheus Metrics]
        Jaeger[Jaeger Tracing]
        Grafana[Grafana Dashboards]

        subgraph LogPipeline["Logs Pipeline"]
            Promtail[Promtail / FluentBit Log Agent]
            LogStore[Loki / OpenSearch / Elastic]
        end
    end

    %% Data Layer (bottom)
    subgraph DataLayer["Data Layer"]
        DB[(PostgreSQL Database)]
    end

    %% Request Flow
    Client -->|HTTP requests| App
    App --> ItemsEndpoint
    ItemsEndpoint -->|SQL queries| DB

    %% Metrics Flow
    App --> MetricsEndpoint
    Prometheus -.->|scrapes metrics| MetricsEndpoint
    Grafana -.->|reads metrics| Prometheus

    %% Tracing Flow
    App -->|trace spans| OTel
    OTel -->|OTLP| Jaeger
    Grafana -.->|trace links| Jaeger

    %% Logs Flow
    App -->|stdout logs| Logs
    Promtail -.->|reads logs| Logs
    Promtail -->|pushes logs| LogStore
    Grafana -.->|logs query| LogStore

    %% Styling
    style App fill:#e85d04,stroke:#dc2f02,stroke-width:3px,color:#fff
    style ItemsEndpoint fill:#ffba08,stroke:#faa307,stroke-width:2px,color:#000
    style MetricsEndpoint fill:#ffba08,stroke:#faa307,stroke-width:2px,color:#000
    style OTel fill:#f5a800,stroke:#d89000,stroke-width:2px,color:#000
    style Logs fill:#6c757d,stroke:#495057,stroke-width:2px,color:#fff

    style DB fill:#336791,stroke:#2d5a7b,stroke-width:2px,color:#fff

    style Prometheus fill:#e6522c,stroke:#c93a1f,stroke-width:2px,color:#fff
    style Jaeger fill:#60d0e4,stroke:#4db8ca,stroke-width:2px,color:#000
    style Grafana fill:#f46800,stroke:#d85600,stroke-width:2px,color:#fff

    style Promtail fill:#1f78b4,stroke:#145684,stroke-width:2px,color:#fff
    style LogStore fill:#7cb342,stroke:#558b2f,stroke-width:2px,color:#fff
    style LogPipeline fill:#ffffff,stroke:#999,stroke-width:1px,color:#000