Amazon has made it much easier to use the Amazon CloudWatch Agent by making it open source (https://github.com/aws/amazon-cloudwatch-agent/), available via package managers, and including a configuration wizard. Here are my notes on my initial testing.

• Update EC2 instance role to include new IAM policy CloudWatchAgentServerPolicy
  • https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/create-iam-roles-for-cloudwatch-agent-commandline.html
• Install CloudWatch Agent via yum
  • sudo yum -y install amazon-cloudwatch-agent
  • https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/download-cloudwatch-agent-commandline.html
• Run the Amazon CloudWatch Agent Configuration Wizard
  • sudo /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-config-wizard
  • If you are using another agent like DataDog you will not be able to use StatsD
  • If you wish to use collectd you will need to install and configure it
• Start the Amazon CloudWatch Agent
  • sudo /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl
  • The default config file location used by the configuration wizard is /opt/aws/amazon-cloudwatch-agent/bin/config.json
  • If you receive error messages try disabling StatsD and collectd via the configuration wizard
  • https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/troubleshooting-CloudWatch-Agent.html

Example command to start the CloudWatch Agent

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

Amazon also has CloudFormation templates that will pre-install and configure the Amazon CloudWatch Agent.
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/Install-CloudWatch-Agent-New-Instances-CloudFormation.html

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "cloudwatch:PutMetricData"
            ],
            "Resource": [
                "*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "cloudwatch:GetMetricStatistics"
            ],
            "Resource": [
                "*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "cloudwatch:ListMetrics"
            ],
            "Resource": [
                "*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "ec2:DescribeTags"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}

*/5 * * * * /root/aws-scripts-mon/mon-put-instance-data.pl --mem-util --mem-used --mem-avail

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/mon-scripts.html