Application Monitor

A Go-based service monitoring tool that checks the health of web applications and sends email and webhook notifications when issues are detected.

Features

• Monitors multiple web applications simultaneously
• Configurable check intervals
• Email notifications for service outages
• Webhook notifications with JSON payloads
• HMAC-SHA256 signature support for webhook security
• Alert after two consecutive failures
• Recovery notifications when service is restored
• JSON-based configuration

Configuration

Create a config.json file with the following structure:

{
  "check_interval": "30s",
  "email": {
    "smtp_host": "smtp.example.com",
    "smtp_port": "587",
    "username": "your-email@example.com",
    "password": "your-password",
    "from_email": "monitor@example.com",
    "to_email": "alerts@example.com"
  },
  "webhook": {
    "enabled": true,
    "url": "https://your-webhook-endpoint.com/alerts",
    "secret": "optional-hmac-secret"
  },
  "applications": [
    {
      "name": "Example App",
      "url": "https://example.com/health",
      "enabled": true,
      "expected_code": 200
    }
  ]
}

Webhook Configuration

The webhook feature allows sending HTTP POST notifications to external systems when applications fail or recover.

Configuration Options:

• enabled: Set to true to enable webhook notifications
• url: The HTTP endpoint that will receive webhook notifications
• secret: (Optional) HMAC secret for payload signature verification

Webhook Events:

• application_down: Sent after 2 consecutive failures
• application_recovery: Sent when application recovers

Webhook Payload:

{
  "event": "application_down",
  "application": "Example App",
  "url": "https://example.com/health",
  "timestamp": 1627843200,
  "status_code": 500,
  "expected_code": 200,
  "error": "connection timeout",
  "failure_count": 2
}

Security: When a secret is configured, webhooks include an X-AppMonitor-Signature header with HMAC-SHA256 signature:

X-AppMonitor-Signature: sha256=abc123...

Supported Integrations:

• Zapier
• Discord webhooks
• Slack webhooks
• Custom HTTP endpoints
• Monitoring systems (PagerDuty, etc.)

Building

go build -o monitor main.go

Running

./monitor config.json

Building/Running for FreeBSD environment

GOOS=freebsd GOARCH=amd64 go build -o monitor main.go

Deploy to remote server

scp monitor host:/srv/app-monitor/monitor
scp config.json host:/srv/app-monitor/config.json

Run as daemon

daemon -p /var/run/app-monitor.pid -o /var/log/app-monitor.log /srv/app-monitor/monitor /srv/app-monitor/config.json