v1.0 Webhook script for Internet connectivity loss on specific interface

#!/bin/bash

# Default values for options
PING_IP="8.8.8.8"      # Default ping IP address (Google DNS)
DNS_CHECK_ADDRESS="github.com"  # Default DNS check address
INTERFACE="eth0"      # Replace with your Ethernet interface name (e.g., eth0)
WEBHOOK_URLS="YOUR_WEBHOOK_URL"  # Default webhook URL(s) (comma-separated)
ENABLE_RESTORE_NOTIFICATION=true   # Set this to false if you want to disable the notification when connectivity is restored
LOCK_FILE="/tmp/internet_monitor.lock" # Define the lock file path

# Function to acquire the lock
acquire_lock() {
    if [[ -e "$LOCK_FILE" ]]; then
        echo "Lock file exists. Script is already running or a previous run didn't finish."
        exit 1
    fi
    touch "$LOCK_FILE"
}

# Function to release the lock
release_lock() {
    rm -f "$LOCK_FILE"
}

# Function to send a webhook notification
send_webhook_notification() {
    local message="$1"
    local urls=($(echo "$WEBHOOK_URLS" | tr ',' ' '))  # Convert comma-separated URLs to an array
    for url in "${urls[@]}"; do
        curl -X POST -H "Content-Type: application/json" -d "{\"text\":\"$message\"}" "$url"
    done
}

# Function to check internet connectivity
check_internet_connectivity() {
    local ip_address="$1"
    if ping -I "$INTERFACE" -c 1 "$ip_address" &> /dev/null; then
        return 0  # Internet connectivity is available
    else
        return 1  # Internet connectivity is not available
    fi
}

# Function to check DNS resolution
check_dns_resolution() {
    local dns_address="$1"
    if ping -I "$INTERFACE" -c 1 "$dns_address" &> /dev/null; then
        return 0  # DNS resolution is successful
    else
        return 1  # DNS resolution failed
    fi
}

# Main function to monitor internet connectivity and DNS resolution
main() {
    if ! check_internet_connectivity "$PING_IP"; then
        # Internet connectivity is not available, send webhook notification with a specific payload
        message="Internet connectivity is down on $INTERFACE at $(date)"
        send_webhook_notification "$message" "connectivity_down"
    elif ! check_dns_resolution "$DNS_CHECK_ADDRESS"; then
        # DNS resolution failed, send webhook notification
        message="DNS resolution failed on $INTERFACE at $(date)"
        send_webhook_notification "$message" "dns_failure"
    else
        # Internet connectivity and DNS resolution are both successful
        if $ENABLE_RESTORE_NOTIFICATION; then
            # Internet connectivity is restored, send webhook notification with a specific payload
            message="Internet connectivity restored on $INTERFACE at $(date)"
            send_webhook_notification "$message" "connectivity_restored"
        fi
    fi
}


# Function to display usage information
usage() {
    echo "Usage: $0 [-p ping_ip_address] [-d dns_check_address] [-w webhook_urls]"
    echo "Options:"
    echo "  -p ping_ip_address       Specify the IP address for internet connectivity check (default: 8.8.8.8)"
    echo "  -d dns_check_address     Specify the DNS address for DNS resolution check (default: github.com)"
    echo "  -w webhook_urls          Specify one or multiple webhook URLs as a comma-separated list"
    exit 1
}

# Parse command-line options using getopts
while getopts ":p:d:w:" opt; do
    case "$opt" in
        p) PING_IP=$OPTARG ;;
        d) DNS_CHECK_ADDRESS=$OPTARG ;;
        w) WEBHOOK_URLS=$OPTARG ;;
        \?) echo "Invalid option: -$OPTARG" >&2 ; usage ;;
        :) echo "Option -$OPTARG requires an argument." >&2 ; usage ;;
    esac
done

# Acquire the lock before starting the main loop
acquire_lock

# Run the main loop
while true; do
    main
    sleep 1m  # Adjust the time interval as needed for internet connectivity and DNS resolution checks
done

# Release the lock when the script exits
release_lock