# AWS CloudWatch When you run applications on AWS, you must always know: * Is my server running? * Is CPU high? * Did my app crash? * Are users getting errors? AWS **CloudWatch** answers all these questions. CloudWatch is the **monitoring and observability service** of AWS. It helps you **see, log, alert, and react** to everything happening in your cloud. --- ## **What is AWS CloudWatch** CloudWatch is a service that: * Collects data from AWS resources * Stores logs * Tracks performance * Sends alerts * Triggers actions In simple words: > CloudWatch is the health monitor of your AWS infrastructure. --- ## **Why CloudWatch is Important** Imagine you have: * EC2 running a website * RDS database * Load Balancer If something breaks at 2 AM, CloudWatch can: * Detect the problem * Send you an alert * Or even auto fix it Without CloudWatch, you are blind. --- # **Main Components of CloudWatch** CloudWatch has five main parts: 1. Metrics 2. Logs 3. Log Groups and Log Streams 4. Alarms 5. Dashboards and Events Let’s understand them one by one. --- ## **1\. CloudWatch Metrics** Metrics are **numbers that show performance**. Examples: * CPU utilization of EC2 * Memory usage * Network traffic * Disk read and write AWS automatically sends basic metrics for: * EC2 * RDS * ELB * Lambda Example: ```plaintext CPUUtilization = 75% ``` This means your EC2 is using 75 percent CPU. You use metrics to: * Monitor performance * Detect overload * Trigger alarms --- ## **2\. CloudWatch Logs** Logs are **text records of what happened**. Examples: * Application errors * Login activity * System messages * Web server logs Your EC2 does not send logs automatically. You must install **CloudWatch Agent** to send logs. Example logs: ```plaintext User logged in Database connection failed 404 error ``` Logs help you debug problems. --- ## **3\. Log Groups and Log Streams** CloudWatch logs are organized in two parts. ### **Log Group** A Log Group is a **folder**. Example: * /aws/ec2/app-logs * /aws/lambda/myFunction ### **Log Stream** A Log Stream is **one source of logs** inside the group. Example: * One EC2 * One application * One container So: Log Group = Folder Log Stream = File inside the folder --- ## **4\. CloudWatch Alarms** An alarm watches a metric and takes action. Example: * If CPU > 80 percent * For 5 minutes * Then send email You can use alarms to: * Send notifications * Restart EC2 * Trigger Auto Scaling Example: ```plaintext If CPUUtilization > 80% → Send alert ``` This keeps your system safe. --- ## **5\. CloudWatch Dashboard** Dashboard shows all metrics in one place. You can create graphs for: * CPU * Memory * Requests * Errors This is useful for: * DevOps teams * Monitoring live systems You can see the health of your whole app on one screen. --- ## **6\. CloudWatch Events (EventBridge)** Events allow AWS services to talk to each other. Example: * EC2 stopped * Lambda failed * S3 file uploaded CloudWatch Events can trigger: * Lambda * SNS * Auto Scaling * Scripts Example: ```plaintext If EC2 stops → Send email ``` This helps automate reactions. --- ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1768207696638/0902f676-0da4-4d6f-8016-5054c14628ba.png align="center") ## **Real Example** You have: * EC2 running a website You setup: * CPU metric * Alarm at 80 percent * Notification via email If traffic increases: * CPU goes high * Alarm triggers * You get alert * Auto Scaling adds new EC2 This is how production systems work. --- ## **When to Use CloudWatch** Use CloudWatch when: * You deploy an application * You want to track performance * You want to detect failures * You want automatic alerts * You want to analyze logs Basically, always use it. --- ## **Why CloudWatch is Critical** Without CloudWatch: * You don’t know if your app is down * You don’t know why errors happened * You cannot auto scale * You cannot detect attacks With CloudWatch: * Full visibility * Real time alerts * Better reliability --- ## **Final Thoughts** CloudWatch is the eyes and ears of AWS. It helps you: * Monitor * Analyze * Alert * Automate If you want to become a real **Cloud or DevOps engineer**, you must know CloudWatch. # CloudWatch interview questions ## **Basic Questions** **1\. What is AWS CloudWatch?** CloudWatch is a monitoring service that collects metrics, logs, and events from AWS resources to track performance and health. **2\. What can you monitor using CloudWatch?** EC2, RDS, ELB, Lambda, DynamoDB, S3, custom applications, and almost any AWS service. **3\. What are CloudWatch Metrics?** Metrics are numeric data like CPU usage, memory, disk, network traffic, and request count. **4\. What are CloudWatch Logs?** Logs store application and system messages that help in debugging and troubleshooting. --- ## **Intermediate Questions** **5\. What is a Log Group?** A Log Group is a container for related log streams. **6\. What is a Log Stream?** A Log Stream is a single source of logs like one EC2 instance or one application. **7\. What is a CloudWatch Alarm?** An alarm monitors a metric and triggers an action when a condition is met. **8\. What actions can CloudWatch Alarms trigger?** Send SNS notification, start or stop EC2, or trigger Auto Scaling. **9\. Does CloudWatch monitor memory by default?** No. Memory and disk must be collected using CloudWatch Agent. --- ## **Advanced Questions** **10\. What is CloudWatch Events?** It is used to react to AWS service changes like EC2 stop, S3 upload, or Lambda failure. **11\. How does CloudWatch help in Auto Scaling?** CloudWatch alarms trigger Auto Scaling policies based on CPU or other metrics. **12\. What is a custom metric?** A metric you send manually to CloudWatch from your own application. --- ## **Real Scenario Questions** **13\. Your EC2 is slow. How will you use CloudWatch?** Check CPU, network, and disk metrics. Check logs for errors. Create alarms. **14\. How will you monitor Apache logs?** Install CloudWatch Agent and send `/var/log/httpd/access_log` to CloudWatch. **15\. How do you get notified if a server goes down?** Create a CloudWatch alarm on instance status check and connect it to SNS.