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Problem:
An EC2 instance stops sending system metrics like CPU, memory, and disk I/O to CloudWatch.
Performance monitoring is disrupted, making it hard to troubleshoot proactively.
Step-by-Step Troubleshooting:
Check Agent Status and Logs:
Log into the EC2 instance via SSH.
Check the status of the CloudWatch Agent using commands like sudo systemctl status amazon-cloudwatch-agent.
Review the agent logs located at /opt/aws/amazon-cloudwatch-agent/logs/ for any errors or warnings.
Identify issues such as misconfigured files, permission errors, or network problems in the logs.
Validate the Configuration File:
Locate the CloudWatch Agent configuration file, usually in JSON format.
Verify that the file includes all necessary metrics like CPU, memory, and disk I/O.
Use the command amazon-cloudwatch-agent-ctl -a fetch-config -m ec2 -c file:<path-to-config> to reload the configuration.
Ensure there are no syntax errors in the configuration file.
Verify IAM Permissions:
Check the IAM role attached to the EC2 instance.
Ensure it has the required permissions, such as cloudwatch:PutMetricData.
If needed, attach the Amazon managed policy CloudWatchAgentServerPolicy to the IAM role.
Confirm that temporary credentials are valid and not expired.
Update and Restart the Agent:
Check if the CloudWatch Agent is running the latest version.
Update the agent if an older version is in use.
Restart the agent using sudo systemctl restart amazon-cloudwatch-agent.
Monitor if metrics start appearing in CloudWatch after the restart.
Test Connectivity:
Use curl to test connectivity to the CloudWatch endpoints.
Confirm that the instance can reach URLs like https://monitoring.<region>.amazonaws.com.
Rule out VPC-level network issues, such as blocked outbound traffic or DNS resolution failures.
Ensure the instance has proper internet access or VPC endpoints if in a private subnet.
Key AWS Terms:
CloudWatch Agent: A tool that collects and sends metrics and logs to CloudWatch.
IAM Role: A set of permissions assigned to an EC2 instance to allow it to interact with AWS services.
CloudWatch: AWS service for monitoring and observability.
Configuration File: A JSON file defining which metrics the CloudWatch Agent should collect.
VPC Endpoints: Private connections to AWS services from within a VPC.
Interview Insight:
When CloudWatch metrics stop reporting, I start by checking the agent logs and configuration for issues.
I verify that IAM roles are correctly set up with permissions to publish metrics.
I also check for network issues that might prevent communication with CloudWatch and ensure the agent is up to date and running properly.