function Get-InstanceHostname {

<#
.SYNOPSIS
    Gets the hostname for an EC2 instance.

.PARAMETER Instance
    [Amazon.EC2.Model.Instance] The instance under inspection.

.EXAMPLE
    Get-InstanceHostname -Instance (Get-CurrentInstance)

APP1611088
#>

    [OutputType([string])]
    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $true)]
        [ValidateNotNull()]
        [Amazon.EC2.Model.Instance]$Instance
    )

    $logLead = (Get-LogLeadName)

    [string] $hostname = ($instance.Tags | Where-Object { $_.Key -eq $Global:AlkamiTagKeyHostName } | Select-Object -First 1).Value

    if ( [string]::IsNullOrEmpty( $hostname ) ) {

        Write-Warning ( "{0} : No hostname found for {1}" -f $logLead, $instance.InstanceId )
        $hostname = $null

    } else {

        $hostname = $hostname.ToUpperInvariant()
    }

    return $hostname
}