function Invoke-StopServers {
<#
.SYNOPSIS
This wraps the APIGateway/Lambda for scaling environments.  Helper for the MinimizeDesignation/MaximizeDesignation functions.

.DESCRIPTION
Sends Shutdown command to all EC2 instances where the alk:hostname tag value = parameter HostnamesCSV.

.PARAMETER Fqdn
Fully Qualified Domain Name of the API Gateway.  Each environment/account has a unique API Gateway endpoint.

.PARAMETER HostnamesCSV
alk:hostname tag to filter which instances to stop. Comma-seperated list. Case sensitive.

.PARAMETER ApiGatewayKey
Unique key for authenticating to the API Gateway.

.EXAMPLE
Invoke-StartServers -fqdn "vyq7hqcx55.execute-api.us-east-1.amazonaws.com" -hostnamesCsv "web27425" -apiGatewayKey "123456789"

returns JSON:
[
    {
        "IsExcluded": false,
        "IsApp": false,
        "IsMic": false,
        "IsWeb": true,
        "IsRunning": false,
        "IsStopped": true,
        "InstanceId": "i-0fa21749b4e4b81ea",
        "Designation": "ci1",
        "HostName": "web27425",
        "Environment": "dev",
        "Service": "orb"
    }
]
.NOTES
Dev FQDN : vyq7hqcx55.execute-api.us-east-1.amazonaws.com
Staging FQDN : cox3133b67.execute-api.us-east-1.amazonaws.com
Qa FQDN :
#>
    [CmdletBinding()]

    Param (
        [Parameter(Mandatory = $true)]
        [string] $Fqdn,
        [Parameter(Mandatory = $true)]
        [string] $ApiGatewayKey,
        [Parameter(Mandatory = $true)]
        [string] $HostnamesCSV

    )

    [System.Net.ServicePointManager]::SecurityProtocol = "Tls12"

    $HostnamesCSV = $HostnamesCSV.Replace(',', '","')

    $jsonBody = '{"Hostnames":["' + $HostnamesCSV + '"]}'
    $response = Invoke-RestMethod -Uri "https://$Fqdn/Prod/StopServers" -Headers @{"x-api-key"="$ApiGatewayKey"} -Method POST -body $jsonBody -ContentType "application/json"

    return $response
}