Replacing Nagios with CloudWatch Agent for EC2 Monitoring
A company is migrating its on-premises applications to AWS and wants to maintain the same level of monitoring for its Linux-based EC2 instances. They currently use Nagios for monitoring. They want a managed AWS service that can monitor instance health, system metrics, and application logs. Which solution should they use?
Quick Answer
The correct solution is to install the Amazon CloudWatch agent on each EC2 instance to collect system metrics and logs, and send them to CloudWatch. This is because the CloudWatch unified agent replaces the functionality of Nagios by providing a single, managed service that captures detailed system-level metrics (like memory and disk usage) and application logs from Linux instances, which the basic EC2 metrics cannot provide. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of migrating from third-party monitoring tools to native AWS services, often appearing in questions that contrast CloudWatch with AWS Systems Manager Inventory, CloudTrail, or Config. A common trap is confusing CloudTrail (API auditing) or Config (compliance) with real-time monitoring, but remember: CloudWatch is for metrics and logs, while the others serve different purposes. Memory tip: think of CloudWatch as your "watch" for health and logs, not just a trail or config checker.
⚠ Common exam trap
The trap is confusing AWS monitoring services: CloudTrail (API audit), Config (configuration compliance), and Systems Manager Inventory (metadata) are often mistaken for a metrics/logs monitoring solution, but only the CloudWatch agent collects guest OS metrics and application logs.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Install the Amazon CloudWatch agent on each EC2 instance to collect system metrics and logs, and send them to CloudWatch.
The CloudWatch agent is the managed AWS solution for collecting guest-level system metrics (memory, disk, swap) and application/system logs from EC2 instances and delivering them to CloudWatch. It replaces the need for a self-managed Nagios server by providing native metric and log ingestion, alarms, and dashboards. Installing it on each instance satisfies the requirement for instance health, system metrics, and application logs in a managed service.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Install the Amazon CloudWatch agent on each EC2 instance to collect system metrics and logs, and send them to CloudWatch.
Why this is correct
The CloudWatch agent runs on each instance to collect system metrics and application logs, then ships them to CloudWatch. This delivers the managed monitoring service the company requires, replacing Nagios without self-managed infrastructure, and satisfies the instance health, metrics and logs monitoring requirement.
- ✗
Use AWS CloudTrail to monitor instance activity and capture log files.
Why it's wrong here
CloudTrail records AWS API calls made against your account, so it captures control-plane actions rather than EC2 system metrics or application log content. It is correct when you need an audit trail of who invoked which API and when.
- ✗
Use AWS Systems Manager Inventory to collect system configuration and log files.
Why it's wrong here
Systems Manager Inventory gathers installed applications, network configuration and file metadata on a schedule; it neither publishes system metrics nor streams application logs. It fits when you need an inventory of software and OS details across a fleet.
- ✗
Use AWS Config to track instance configuration changes and trigger alerts.
Why it's wrong here
AWS Config records resource configuration state and evaluates compliance rules; it does not collect CPU, memory or disk metrics, nor ingest application logs. It is the right choice when you need configuration drift detection and compliance auditing across accounts.
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Variation 1. A DevOps engineer is designing a monitoring solution for an application that runs on Amazon EC2 instances in an Auto Scaling group. The engineer needs to collect memory utilization metrics and visualize them in a dashboard. What should the engineer do?
medium- A.Create a custom CloudWatch metric namespace and publish memory data using the AWS CLI.
- ✓ B.Install the Amazon CloudWatch agent on the EC2 instances to collect memory metrics and publish them to CloudWatch.
- C.Enable detailed monitoring on the EC2 instances to collect memory metrics.
- D.Use AWS CloudTrail to capture memory utilization events from the EC2 instances.
Why B: The Amazon CloudWatch agent is required to collect memory utilization metrics from EC2 instances because memory usage is not a default metric provided by CloudWatch. By installing the CloudWatch agent on the instances, it can gather memory metrics (and other custom metrics) and publish them to CloudWatch, where they can be visualized in dashboards. This is the standard AWS-recommended approach.
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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