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consul-monitor/design.md
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Consul Service Monitor - Design Document

Overview

A web-based dashboard application that monitors and visualizes the health status of services registered in HashiCorp Consul. The application provides real-time monitoring with historical health tracking capabilities.

Architecture

High-Level Components

  1. Web Frontend - Interactive dashboard displaying service status
  2. Backend API - REST API for data retrieval and configuration
  3. Data Collection Service - Background service polling Consul for health data
  4. SQLite Database - Historical health check data storage
  5. Consul Integration - Service discovery and health check monitoring

Technology Stack

  • Frontend: HTML5, CSS3, JavaScript (with Chart.js for visualizations)
  • Backend: Python 3.9+ with Flask
  • Database: SQLite (ephemeral storage)
  • Service Discovery: HashiCorp Consul (consul.service.dc1.consul)
  • Updates: Periodic polling (no WebSockets needed)

Functional Requirements

Core Features

1. Service List Display

  • Display all services registered in Consul
  • Show service name, ID, and tags
  • Provide clickable links to service URLs
  • Support sorting and filtering

2. Health Status Visualization

  • Current Status Indicator
    • Green icon: All health checks passing
    • Red icon: One or more health checks failing
    • Yellow icon: Warning state (if supported)
  • Historical Status Chart
    • Mini bar chart showing 24-hour health history
    • Time-based visualization (hourly aggregation)
    • Color-coded status representation

3. Auto-refresh Functionality

  • Toggle switch to enable/disable auto-refresh
  • Configurable refresh interval (30s, 1m, 2m, 5m, 10m)
  • Visual indicator when auto-refresh is active
  • Manual refresh button

4. Configuration Management

  • Session-based storage of user preferences (no persistence needed)
  • Configurable history granularity (5m, 15m, 30m, 1h) - default: 15 minutes

Database Schema

Tables

-- Services table
CREATE TABLE services (
    id TEXT PRIMARY KEY,
    name TEXT NOT NULL,
    address TEXT,
    port INTEGER,
    tags TEXT, -- JSON array
    meta TEXT, -- JSON object
    first_seen DATETIME DEFAULT CURRENT_TIMESTAMP,
    last_seen DATETIME DEFAULT CURRENT_TIMESTAMP
);

-- Health checks table
CREATE TABLE health_checks (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    service_id TEXT NOT NULL,
    check_id TEXT NOT NULL,
    check_name TEXT,
    status TEXT NOT NULL, -- 'passing', 'warning', 'critical'
    output TEXT,
    timestamp DATETIME DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (service_id) REFERENCES services (id)
);

-- Configuration table (session-based, optional for defaults)
CREATE TABLE config (
    key TEXT PRIMARY KEY,
    value TEXT NOT NULL,
    updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
);

-- Service URLs are generated using pattern: http://{service_name}.service.dc1.consul:{port}

-- Indexes for performance
CREATE INDEX idx_health_checks_service_timestamp ON health_checks (service_id, timestamp);
CREATE INDEX idx_health_checks_timestamp ON health_checks (timestamp);

API Design

REST Endpoints

# Flask routes
GET /
- Serves main dashboard HTML page

GET /api/services
- Returns list of all services with current health status
- Generated URLs: http://{service_name}.service.dc1.consul:{port}
- Response: Array of service objects with health summary

GET /api/services/<service_id>/history
- Returns historical health data for charts
- Query params: ?granularity=15 (minutes: 5,15,30,60)
- Response: Time-series data for Chart.js

POST /api/config
- Updates session configuration
- Body: { "autoRefresh": true, "refreshInterval": 60, "historyGranularity": 15 }

GET /api/config
- Returns current session configuration

Data Collection Service

Polling Strategy

Consul Polling:
  - Interval: 60 seconds
  - Consul Address: consul.service.dc1.consul:8500
  - Endpoints:
    - /v1/agent/services (service discovery)
    - /v1/health/service/{service} (health checks)
  - No authentication required
  - Error handling: Log errors, continue polling
  - Expected services: 30-40 services

Data Retention:
  - Keep detailed data for 24 hours only (ephemeral storage)
  - No long-term aggregation needed
  - Database recreated on container restart

Health Check Processing

  1. Data Collection

    • Poll Consul API for service list
    • For each service, fetch health check status
    • Store raw health check data with timestamps

  2. Status Aggregation

    • Service-level status: Worst status among all checks
    • Historical aggregation: Count of passing/warning/critical per time window

  3. Change Detection

    • Compare current status with previous poll
    • Trigger notifications/updates on status changes
    • Maintain service registration/deregistration events

Frontend Design

Main Dashboard Layout

┌─────────────────────────────────────────────────┐
│ Consul Service Monitor              [⚙️] [🔄]   │
├─────────────────────────────────────────────────┤
│ Auto-refresh: [ON/OFF] Interval: [1m ▼]           │
│ History granularity: [15m ▼]                      │
├─────────────────────────────────────────────────┤
│ Service Name    │ Status │ URL      │ History   │
├─────────────────┼────────┼──────────┼───────────┤
│ web-api         │ 🟢     │ [link]   │ ▆▆█▆█▆▆  │
│ database        │ 🔴     │ [link]   │ █▆▆▄▂▂▄  │
│ cache-service   │ 🟢     │ [link]   │ ████████  │
└─────────────────────────────────────────────────┘

Interactive Elements

  • Status Icons: Visual indicators only (no detailed popup needed)
  • History Charts: Chart.js mini bar charts with 24-hour data
  • Service Links: URLs generated as http://{service_name}.service.dc1.consul:{port}
  • Desktop-optimized: No mobile responsive design required

Updates

  • Periodic AJAX polling for updates
  • Configurable refresh intervals (30s, 1m, 2m, 5m, 10m)
  • Visual loading indicators during refresh

Configuration Management

User Settings (Session-based)

{
  "autoRefresh": {
    "enabled": false,
    "interval": 60,
    "options": [30, 60, 120, 300, 600]
  },
  "display": {
    "historyGranularity": 15,
    "granularityOptions": [5, 15, 30, 60]
  }
}

System Configuration

# Flask configuration
CONSUL_HOST = "consul.service.dc1.consul"
CONSUL_PORT = 8500
DATABASE_PATH = ":memory:"  # Ephemeral SQLite
POLL_INTERVAL = 60  # seconds
MAX_SERVICES = 50  # Safety limit

Deployment Considerations

Docker Deployment

FROM python:3.11-slim

WORKDIR /app

# Install dependencies
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Copy application
COPY . .

# Expose port
EXPOSE 5000

# Set environment variables
ENV FLASK_APP=app.py
ENV FLASK_ENV=production
ENV CONSUL_HOST=consul.service.dc1.consul
ENV CONSUL_PORT=8500

# Health check
HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
  CMD curl -f http://localhost:5000/health || exit 1

CMD ["python", "-m", "flask", "run", "--host=0.0.0.0"]

Python Dependencies (requirements.txt)

Flask==2.3.3
requests==2.31.0
sqlite3  # Built-in
APScheduler==3.10.4  # For background polling

Environment Variables

  • CONSUL_HOST: Consul server hostname (default: consul.service.dc1.consul)
  • CONSUL_PORT: Consul server port (default: 8500)
  • FLASK_PORT: Web server port (default: 5000)
  • POLL_INTERVAL: Health check polling interval in seconds (default: 60)

Health Checks

The application should expose its own health endpoint:

  • GET /health: Returns application health status
  • GET /metrics: Prometheus-style metrics (optional)

Security Considerations

  1. Consul Access: No authentication required for your setup
  2. Database: Ephemeral SQLite in container memory
  3. Web Interface: Open dashboard, no authentication needed
  4. Input Validation: Sanitize service names and configuration inputs
  5. Container Security: Run as non-root user in container

Future Enhancements

  • Alerting: Email/Slack notifications on service failures (mentioned as future feature)
  • Service Filtering: Search and filter capabilities for larger service lists
  • Service Details: Detailed health check information popup/modal
  • Themes: Dark/light mode toggle
  • Export: Export health data as CSV/JSON
  • Custom Time Ranges: Configurable history periods beyond 24 hours

Development Phases

Phase 1: Core Functionality

  • Basic Consul integration
  • SQLite database setup
  • Simple web interface
  • Manual refresh capability

Phase 2: Real-time Features

  • Auto-refresh functionality
  • WebSocket integration
  • Historical data visualization
  • Configuration persistence

Phase 3: Enhanced UX

  • Responsive design
  • Advanced filtering
  • Performance optimizations
  • Error handling improvements

Phase 4: Production Ready

  • Docker deployment
  • Security hardening
  • Monitoring and logging
  • Documentation and testing
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