Artem Butusov Blog
sormy.nm.ru
github.com/sormy
linkedin.com/in/sormy

Check CPU credits on AWS t2 instances

Author Artem Butusov · Published on January 1st, 2018

Contents

t2 instances and gentoo

AWS t2 instances could be a bad choice for compilation of heavy application, especially on Gentoo without binary repo. Before upgrading any heavy package like gcc, glibc, kernel it is good to check if your instance has enough CPU credits to compile package without falling back to baseline performance.

You could read more about t2 instance here: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/t2-credits-baseline-concepts.html

script to check cpu credits

You could easily check CPU credits with small bash script below:

#!/bin/bash

CPU_CREDITS_WARN=50 # in percents

# https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/t2-credits-baseline-concepts.html
instance_type_max_cpu_credits_t2_nano=72
instance_type_max_cpu_credits_t2_micro=144
instance_type_max_cpu_credits_t2_small=288
instance_type_max_cpu_credits_t2_medium=576
instance_type_max_cpu_credits_t2_large=864
instance_type_max_cpu_credits_t2_xlarge=1296
instance_type_max_cpu_credits_t2_2xlarge=1944

metadata="$(curl -sL http://169.254.169.254/latest/dynamic/instance-identity/document)" 
region=$(echo "$metadata" | jq -r .region)
instance_id=$(echo "$metadata" | jq -r .instanceId)
instance_type=$(echo "$metadata" | jq -r .instanceType)

start_time=$(date -u -d "10 minutes ago" +%Y-%m-%dT%H:%M:%S)
end_time=$(date -u +%Y-%m-%dT%H:%M:%S)

cpu_credits_metadata=$(
    aws cloudwatch get-metric-statistics \
        --namespace AWS/EC2 \
        --region ${region} \
        --metric-name CPUCreditBalance \
        --start-time "${start_time}" \
        --end-time "${end_time}" \
        --period 60 \
        --statistics Average \
        --dimensions Name=InstanceId,Value="${instance_id}" \
    | jq -r '.Datapoints[] | .["Average", "Timestamp"]' | tail -n 2
)

cpu_credits_value=$(echo "$cpu_credits_metadata" | head -n 1)
cpu_credits_ts=$(echo "$cpu_credits_metadata" | tail -n 1)
cpu_credits_max_var=instance_type_max_cpu_credits_${instance_type/./_}
cpu_credits_max=${!cpu_credits_max_var}
cpu_credits_ratio=$(echo "$cpu_credits_value / $cpu_credits_max * 100" | bc -l)
cpu_credits_warn=$(echo "$cpu_credits_ratio <= $CPU_CREDITS_WARN" | bc -l)

echo "Instance ID: $instance_id"
echo "Instance Type: $instance_type"
echo "Region ID: $region"
echo "Timestamp: $cpu_credits_ts"
echo "CPU Credits: $(printf %.0f $cpu_credits_value) / $(printf %.0f $cpu_credits_max) ($(printf %.0f $cpu_credits_ratio)%)"

exit $cpu_credits_warn

script dependencies

Please note, this script depends on bash, jq and aws:

aws configuration

aws requires configuration on instance where you will use it. You could follow official article: https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-quick-configuration

You will also need to grant read access to your user access for cloudwatch.CPUCreditBalance metric thru AWS console.

Your policy could look like (where A.B.C.D is ip address of your instance):

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "cloudwatch:GetMetricStatistics",
            "Resource": "*",
            "Condition": {
                "IpAddress": {
                    "aws:SourceIp": "A.B.C.D/32"
                }
            }
        }
    ]
}

Checklist: