📘 Promtail, Loki, and Grafana Setup Overview

This document explains the roles, flow, and architecture of the Promtail–Loki–Grafana stack used in the Dhanman infrastructure for centralized log management.

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🧩 Components and Their Roles

1. Promtail (Log Collector)

• Purpose: Reads and ships log files from servers.
• Responsibilities:
• Watches log files (e.g., /var/www/prod/logs/*.log).
• Adds contextual labels like service, env, and filename.
• Sends log data to Loki over HTTP.
• Example:

  /var/www/qa/logs/dhanman-purchase-20251015.log → Loki (service=purchase, env=qa)
  

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2. Loki (Log Aggregator / Storage)

• Purpose: Acts as the central database for logs.
• Responsibilities:
• Receives and indexes logs from Promtail.
• Stores logs efficiently in chunks (like Prometheus for logs).
• Supports queries using LogQL (Loki Query Language).
• Example Query:

  {service="purchase", level="Error"}
  

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3. Grafana (Visualizer / Dashboard)

• Purpose: Provides the UI for log exploration and monitoring.
• Responsibilities:
• Connects to Loki as a data source.
• Displays logs in tables, graphs, or custom dashboards.
• Allows filtering, searching, and alert creation.
• Example Usage:
• Dashboard panels for: Recent Error Logs, Log Count by Service, SQL Query Logs.

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⚙️ Data Flow Summary

1. Promtail reads and labels logs.
2. Promtail pushes logs to Loki.
3. Grafana queries Loki to visualize and analyze logs.

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🖼️ Architecture Diagram (Mermaid)

graph TD
    A[Application Logs<br/>/var/www/{env}/logs/*.log] -->|Tails & Labels| B[Promtail<br/>(Log Collector)]
    B -->|Pushes via HTTP| C[Loki<br/>(Log Aggregator & Storage)]
    C -->|Queries via LogQL| D[Grafana<br/>(Dashboard & Visualization)]

    subgraph Environments
    A
    end

    subgraph Dhanman Infrastructure
    B
    C
    D
    end

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🧠 Example: Dhanman QA Setup

Component	Host / Container	Role
Promtail	qa droplet	Collects logs from /var/www/qa/logs/
Loki	Docker container loki	Receives and stores logs
Grafana	Accessible at https://logs.dhanman.com	Visualizes logs and metrics

Promtail Configuration Snippet:

scrape_configs:
  - job_name: "qa-logs"
    static_configs:
      - targets: ["localhost"]
        labels:
          env: "qa"
          __path__: /var/www/qa/logs/*.log

Loki Endpoint:

url: http://loki:3100/loki/api/v1/push

Grafana Panels: - ✅ Recent Error Logs (filtered by service/env) - 📊 Log Count per Service (QA/PROD) - 🔍 SQL Query Logs (Entity Framework tracking)

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🧾 Summary Table

Tool	Function	Acts On	Outputs To
Promtail	Collects logs	Log files	Loki
Loki	Stores & indexes	Logs	Grafana
Grafana	Displays & alerts	Loki	Dashboard/UI

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🚀 Benefits of This Setup

• Centralized log visibility across all services.
• Easy filtering by environment (QA / PROD) and service name.
• Lightweight and efficient (no heavy Elasticsearch setup).
• Integrates seamlessly with existing monitoring (Prometheus, Node Exporter).

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Author: B2A Technologies Pvt. Ltd.
Project: Dhanman Logging & Monitoring Architecture
Date: 2025-10-15