monitor.sh

#!/bin/bash
#
# UPTIME MONITORING
# v1.0.0
#
### INSTALLATION
#
# 1. Install dependencies
#
#       `apt-get install mailx curl openssl`
#
# 2. Setup `monitor.sh` script.
#
#       Copy the script to a easily reachable location and mark it as
#       executable (`chmod +x monitor.h`)
#
# 3. Setup cronjobs.
#
#       It's recommended to run the monitor script at least every 5 minutes.
#       This can be achieved with cronjobs, for example:
#           */5 * * * * sudo /home/ubuntu/monitor.sh example.com
#       This will execute the `monitor.sh` for domain `example.com` at every
#       5th minute.
#

### E-Mail Configuration
readonly SMTP_SERVER="smtp.example.com"
readonly SENDER_EMAIL="noreply@example.com"
readonly RECIPIENT_EMAIL="status@example.com"

### USAGE
readonly domain="$1"
if [ "$domain" = "" ]; then
    echo "usage: monitor.sh domain"
    exit 1
fi


readonly cfgpath="$HOME/.uptimebot"
readonly varfile="$cfgpath/$domain"
mkdir -p "$cfgpath"

function _sendmail() {
    mailx \
        -s "$1" \
        -r "$SENDER_EMAIL" \
        -S smtp="$SMTP_SERVER" \
        -S smtp-use-starttls \
        $RECIPIENT_EMAIL \
        < /dev/null
}

function sendmail() {
    local ts
    ts=$(date "+%s")
    if [ -f "$varfile" ]; then
        readonly lastmail=$(cat "$varfile")
        readonly minutes=$(( ($(date "+%s") - lastmail) / 60 ))
        if (( "$minutes" > 60 )); then
            echo "$ts" > "$varfile"
            _sendmail "$@"
        fi
    else
        echo "$ts" > "$varfile"
        _sendmail "$@"
    fi
}

exitstatus=0
readonly statuscode=$(curl -I -X GET -s -L -o /dev/null -w '%{response_code}' "https://$domain" 2> /dev/null)
if [[ "$statuscode" != "200" ]]; then
    sendmail "$domain: status not 200"
    exitstatus=1
fi

readonly enddate=$(echo | openssl s_client -connect "$domain:443" -servername "$domain" 2> /dev/null | openssl x509 -noout -enddate | cut -b 10-)
readonly timestamp=$(date --date="$enddate" "+%s")
readonly current=$(date "+%s")
readonly hours=$(( (timestamp - current) / 3600 ))

if (( "$hours" < 48 )); then
    sendmail "$domain: certificate expires in $hours hours"
    exitstatus=1
fi

# Remove file if status is ok!
if (( exitstatus == 0 )); then
    if [ -f "$varfile" ]; then
        readonly ts=$(cat "$varfile")
        readonly now=$(date "+%s")
        readonly hour=$(( (now - ts) / 3600 ))
        readonly minute=$(( ((now - ts) % 3600 ) / 60 ))
        printf -v message "offline for %02d:%02d" $hour $minute
        sendmail "$domain: status OK - $message"
    fi
    rm -f "$varfile"
fi