🎯Shell Scripting for Beginners – Part 10: Middleware Health Monitoring Project (Mixed Example).

• This is our final, beginner-friendly project 🎯 — where we'll combine everything you've learned: variables, if-else, loops, functions, logging, and cron automation.
• Let's create a simple Middleware Health Monitoring script that checks Tomcat, Jenkins, Docker, MySQL, and SSL expiry.

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📑 Table of Contents

• 1️⃣ Overview
• 2️⃣ Full Simple Script
• 3️⃣ Example Output
• 4️⃣ Automate the Script

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1️⃣ Overview

This script uses:

• Variables – store names, logs, and domains.
• Functions – reusable checks for each service.
• If-Else – to decide if a service needs restart.
• For loop – to check multiple Docker containers.
• While loop – to retry connection.
• Logs – write output to a file.

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2️⃣ Full Middleware Health Monitoring Script

#!/bin/bash
# MiddlewareBox - Simple Health Monitor

LOG="/var/log/middleware_health.log"
domain="middlewarebox.com"
echo "===== Middleware Health Check =====" >> $LOG
date >> $LOG

# --- Function to check Tomcat ---
check_tomcat() {
  echo "Checking Tomcat..."
  if pgrep -f "org.apache.catalina.startup.Bootstrap" > /dev/null; then
     echo "✅ Tomcat is running" | tee -a $LOG
  else
     echo "🚨 Tomcat is down, restarting..." | tee -a $LOG
     /opt/tomcat/bin/startup.sh
     echo "✅ Tomcat restarted" | tee -a $LOG
  fi
}

# --- Function to check Jenkins ---
check_jenkins() {
  echo "Checking Jenkins..."
  if systemctl is-active --quiet jenkins; then
     echo "✅ Jenkins is active" | tee -a $LOG
  else
     echo "🚨 Jenkins not running, restarting..." | tee -a $LOG
     systemctl restart jenkins
     echo "✅ Jenkins restarted" | tee -a $LOG
  fi
}

# --- Function to check MySQL ---
check_db() {
  echo "Checking MySQL..."
  if mysql -u root -pSecret -e "show databases;" > /dev/null 2>&1; then
     echo "✅ MySQL connection successful" | tee -a $LOG
  else
     echo "🚨 MySQL connection failed" | tee -a $LOG
     echo "Retrying in 5 seconds..."
     sleep 5
     mysql -u root -pSecret -e "show databases;" && echo "✅ MySQL reconnected" | tee -a $LOG
  fi
}

# --- Check Docker Containers using FOR Loop ---
check_docker() {
  echo "Checking Docker containers..."
  for c in nginx webapp db
  do
    status=$(docker inspect -f '{{.State.Status}}' $c 2>/dev/null)
    if [ "$status" != "running" ]; then
      echo "🚨 Container $c is $status, restarting..." | tee -a $LOG
      docker start $c
    else
      echo "✅ Container $c is running" | tee -a $LOG
    fi
  done
}

# --- Check SSL certificate expiry ---
check_ssl() {
  echo "Checking SSL expiry..."
  expiry=$(echo | openssl s_client -servername $domain -connect $domain:443 2>/dev/null | openssl x509 -noout -dates | grep notAfter | cut -d= -f2)
  days_left=$(( ($(date -d "$expiry" +%s) - $(date +%s)) / 86400 ))
  if [ $days_left -le 15 ]; then
    echo "⚠️ SSL expires in $days_left days!" | tee -a $LOG
  else
    echo "✅ SSL valid for $days_left days" | tee -a $LOG
  fi
}

# --- MAIN EXECUTION FLOW ---
check_tomcat
check_jenkins
check_db
check_docker
check_ssl

echo "✅ Health check completed successfully!" | tee -a $LOG
echo "========================================" >> $LOG

💬 Example Output:

✅ Tomcat is running
✅ Jenkins is active
✅ MySQL connection successful
✅ Container nginx is running
✅ SSL valid for 70 days
✅ Health check completed successfully!

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3️⃣ Automate the Script

# Run every 30 minutes
*/30 * * * * /opt/scripts/middleware_health.sh >> /var/log/health_cron.log 2>&1

# Run automatically on system reboot
@reboot /opt/scripts/middleware_health.sh >> /var/log/boot_health.log 2>&1

💬 Output (Cron log):

[BOOT] Health check executed
✅ All services healthy

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🏁 Summary

• ✅ Combined all major shell scripting concepts.
• ✅ Checks Tomcat, Jenkins, Docker, MySQL, and SSL in one file.
• ✅ Uses if, for, functions, and basic while retry logic.
• ✅ Can run manually or via cron / reboot automation.

← Previous: Part 9 – Scheduling & Automation Next: Part 11 – Log Management & Rotation →