How CloudWatch Agent Completes EC2 Monitoring: A Comprehensive Guide

"Why don’t I see my application logs in CloudWatch?"

That was the question bugging Arjun, again. His EC2 instance was running fine, but CloudWatch looked empty. No logs. No memory usage. No granular CPU stats.

Until he discovered CloudWatch Agent — the bridge between your EC2 instance and CloudWatch magic.

💭 First, the Problem

By default, EC2 instances don’t send logs or detailed system metrics to CloudWatch.

You won’t see your /var/log/app.log in CloudWatch Logs.
You won’t get memory or disk space metrics in CloudWatch Metrics.

So how do you fix that?
You install a small agent inside your EC2. That’s it.

🛠️ What is the CloudWatch Agent?

Think of the CloudWatch Agent as your instance’s personal messenger to CloudWatch.

It collects:

🔹 Logs (like application or system logs)
🔹 Metrics (like RAM usage, disk I/O, network stats)

And sends them to CloudWatch in near real-time.

There are two types of agents:

Agent Type	Purpose	Status
CloudWatch Logs Agent	Sends only logs	Old
CloudWatch Unified Agent	Sends logs + metrics	New & Recommended ✅

🚀 Arjun’s Setup Story

Let’s walk through how Arjun set it up:

🧱 Step 1: Attach IAM Role

Arjun created an IAM Role with CloudWatchAgentServerPolicy and attached it to his EC2 instance.
🔐 This gave permission for the agent to push logs and metrics to CloudWatch.

🧩 Step 2: Install the Agent

He used the official CloudWatch Agent installation script for Amazon Linux 2.

sudo yum install amazon-cloudwatch-agent

🧰 Step 3: Configure It

Arjun chose CloudWatch Unified Agent, which can be configured in two ways:

Using a JSON file locally
Or more elegantly, from SSM Parameter Store for centralized setup!

SSM config? Yes — with Unified Agent, he could control multiple agents from one place. No more SSH-ing into 10 servers.

📦 What Did He Get?

After setup, Arjun’s CloudWatch dashboard transformed:

📄 Logs:

/var/log/syslog
/home/app/error.log
Custom logs from his app

📊 Metrics:

Type	Examples
CPU	user, system, idle, steal
RAM	free, used, cache, active
Disk I/O	reads/sec, writes/sec, bytes
Network	TCP/UDP connections, packets, errors
Processes	running, sleeping, dead
Swap	usage, percentage

And guess what? EC2’s default CloudWatch metrics don’t even include memory or swap. You need this agent for those!

💡 Bonus: Works On-Prem Too

Running a server on-premises?
Yes, Arjun did that too. He installed the same Unified Agent on a Linux VM in his local data center — and logs flowed into AWS CloudWatch.

CloudWatch doesn’t care where the server is — as long as the agent is installed and has permissions.

🎓 SAA Exam Tip

✅ Unified CloudWatch Agent = Logs + Granular Metrics + SSM Support
❌ Old Logs Agent = Logs only, no metrics, no SSM
✅ You must give EC2 instances the right IAM role
✅ Works on EC2 or on-prem VMs

🧘 Arjun’s Takeaway

Before the agent, he was blind. After it, he had superpowers.

So next time you're not seeing logs or memory stats from EC2, remember:

Install the CloudWatch Unified Agent.