#!/bin/bash
# two scenarios - either we have gp2 and we check if we do below defined burst balance
# or we have io1 and then we check current consumption and compare against provisioned values
# we can revert back to gp2 if it's really low or increase iops if needed
# if may be interesting to look into decreasing iops provisioning without switching to gp2
# but let's keep it on the safe side for the time being

# Define basic variables
BurstThreshold=30
StartTime=$(TZ=GMT date +%FT%T -d '20 minutes ago')
EndTime=$(TZ=GMT date +%FT%T)
InstancesToCheck=("webworker")

# function to calculate iops consumption
iops () {
    Period=1200
    ReadIops="$(printf "%.0f\n" "$(aws cloudwatch get-metric-statistics --metric-name VolumeReadOps --namespace AWS/EBS \
        --start-time "$1" --end-time "$2" --period ${Period} --statistics Sum --dimensions Name=VolumeId,Value="$3" \
        --query Datapoints[0].Sum)")"

    WriteIops="$(printf "%.0f\n" "$(aws cloudwatch get-metric-statistics --metric-name VolumeWriteOps --namespace AWS/EBS \
        --start-time "$1" --end-time "$2" --period ${Period} --statistics Sum --dimensions Name=VolumeId,Value="$3" \
        --query Datapoints[0].Sum)")"

    IopsPerSec=$((${ReadIops}/${Period} + ${WriteIops}/${Period}))
    return ${IopsPerSec}
}

for instance in ${InstancesToCheck[@]}; do
    echo "---------------------------------"
    echo "Checking volume for ${instance}"
    # Get admins volume
    VolType=$(aws ec2 describe-volumes --filters Name=tag:Name,Values="${instance}" --query 'Volumes[].VolumeType' --output text)
    echo "Volume type detected: ${VolType}"

    VolId=$(aws ec2 describe-volumes --filters Name=tag:Name,Values="${instance}" --query 'Volumes[].Attachments[].VolumeId' --output text)
    if  [[ -n ${VolId} ]]; then
        if [[ ${VolType} == "gp2" ]]; then
            echo "Checking burst balance for volume ${VolId}"
            # Check volume balance
            Balance="$(printf "%.0f\n" "$(aws cloudwatch get-metric-statistics --metric-name BurstBalance --namespace AWS/EBS \
                --start-time "${StartTime}" --end-time "${EndTime}" --period 300 --statistics Average --dimensions Name=VolumeId,Value=${VolId} \
                --query Datapoints[0].Average)")"
            echo "Current burst balance for volume ${VolId} is ${Balance}"

            if [[ "${Balance}" -le "${BurstThreshold}" ]]; then
                echo "Balance below the threshold, volume change to io1 with 3000 iops"
                Result="$(aws ec2 modify-volume --volume-type io1 --iops 3000 --volume-id "${VolId}")"
                echo ${Result}
            else
                echo "Nothing to do on the volume ${VolId}"
            fi
        else
            iops ${StartTime} ${EndTime} ${VolId}
            IopsConsumption=$?
            echo "Current average IOPS consumption for volume ${VolId} is equal ${IopsConsumption}"

            if [[ "${IopsConsumption}" -le "${BurstThreshold}" ]]; then
                Result="$(aws ec2 modify-volume --volume-type gp2 --volume-id "${VolId}")"
                echo ${Result}
                echo "Volume ${VolId} switched back to gp2"
            else
                VolIops=$(aws ec2 describe-volumes --filters Name=tag:Name,Values="${instance}" --query 'Volumes[].Iops' --output text)
                echo "Current IOPS capacity for ${VolId} is equal ${VolIops}"

                MaxIops=$(($VolIops/90*100))

                if [[ "${IopsConsumption}" -ge "${MaxIops}" ]]; then
                    newIops=$((IopsConsumption*2))
                    Result="$(aws ec2 modify-volume --volume-type io1 --iops ${newIops} --volume-id "${VolId}")"
                    echo ${Result}
                    echo "IOPS for volume "{VolId}" increased to ${newIops}"
                else
                    echo "Nothing to do on the volume ${VolId}, max ${MaxIops} has not been reached"
                fi
            fi
        fi
    fi
    echo "---------------------------------"
done