Monitoring AWS EC2 Instances with CloudWatch Custom Metrics

Ever wondered if your EC2 instances are really performing as expected? Maybe you’re noticing sluggish response times or unexpected spikes in costs. That’s where AWS CloudWatch custom metrics come in. While CloudWatch already tracks a lot out of the box, sometimes you need more specific data to truly understand what’s going on under the hood.

Let’s dive into how you can create and use custom metrics to monitor your EC2 instances more effectively.

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What Are CloudWatch Custom Metrics?

Think of CloudWatch as your virtual dashboard for AWS. By default, it gives you metrics like CPU usage, disk reads/writes, and network traffic. But what if you want to monitor things like memory usage, disk space, or even application-specific metrics?

That’s where custom metrics shine. They allow you to send any data you want to CloudWatch, so you can monitor it just like the default metrics.

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Why Custom Metrics Matter

Default metrics are great, but they don’t cover everything. For example:

• Want to know how much free memory is left? Not a default metric.
• Curious about application performance? You’ll need to define what matters most to you.

Custom metrics fill these gaps. They let you track the data that’s critical to your workload, helping you stay ahead of potential problems.

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Setting Up CloudWatch Custom Metrics

Ready to get started? Let’s break this down step-by-step.

Step 1: Install the CloudWatch Agent

First, you’ll need to install the CloudWatch Agent on your EC2 instance. This agent collects system-level metrics and sends them to CloudWatch.

Here’s how to install it on an Amazon Linux 2 instance:

1. Update your system:sudo yum update -y
2. Install the CloudWatch Agent:sudo yum install amazon-cloudwatch-agent -y

You’re halfway there!

Step 2: Configure the Agent

The agent needs a configuration file to know what to monitor. You can create one in JSON format. Here’s a simple example:

{  
  "metrics": {  
    "metrics_collected": {  
      "mem": {  
        "measurement": [  
          "mem_used_percent"  
        ]  
      },  
      "disk": {  
        "measurement": [  
          "used_percent"  
        ],  
        "resources": [  
          "*"  
        ]  
      }  
    }  
  }  
}  

Save this file as config.json.

Step 3: Start the Agent

Once your configuration is ready, start the agent:

sudo /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl \  
  -a fetch-config \  
  -m ec2 \  
  -c file:/path/to/config.json \  
  -s  

If all goes well, your custom metrics will start appearing in the CloudWatch console.

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Viewing Custom Metrics in CloudWatch

Now that your metrics are flowing, it’s time to see them in action.

1. Open the CloudWatch Console.
2. Navigate to Metrics.
3. Select the namespace for your custom metrics (usually CWAgent).
4. Pick the metrics you want to visualize.

You can set alarms, create dashboards, and even integrate them with other AWS services like Lambda or SNS for automated responses.

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Pro Tips for Using Custom Metrics

1. Don’t Overdo It: Sending too many metrics can get expensive. Focus on the ones that really matter.
2. Use Alarms Wisely: Set alarms for critical thresholds, but don’t overwhelm yourself with unnecessary notifications.
3. Tag Your Resources: Use tags to filter and group metrics, especially if you have many instances.

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A Quick Story

A colleague of mine once ignored memory monitoring on their EC2 instances. One day, the application started crashing randomly. After hours of debugging, we realised the issue was out-of-memory errors. If they had set up a custom memory usage metric and an alert, they could’ve avoided the headache. Lesson learned: track what matters!

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Resources

Want to learn more? Here are some links to help you get started:

• AWS CloudWatch Agent Documentation
• EC2 Monitoring Best Practices

For a deeper dive, check out our guide on automating AWS infrastructure with Terraform. It pairs perfectly with CloudWatch for seamless management.

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Setting up custom metrics may seem like a hassle, but the benefits far outweigh the effort. Have you tried monitoring EC2 instances with CloudWatch? What metrics do you track? Let us know in the comments!