Dockerable Prometheus "anything" exporter in PowerShell

promex.ps1

# pwsh "anything" Prometheus exporter sketch
# Using: PrometheusExporter (https://github.com/jobec/powershell-prom-client), including class defintitions
# Using: Polaris (https://github.com/PowerShell/Polaris)
# Motivation: being able to package PowerShell-based collector/exporter in a Docker container 
# PrometheusExporter's 0.1.0 New-PrometheusExporter functionfails when run in a container - [console]::KeyAvailable error
# NOTE: Polaris can process one request at a time. Refactor/implement LB for real use

Using module PrometheusExporter
Import-Module Polaris

# Polaris request logging
function Log-Request([PolarisRequest]$Request) {
    $logentry = '{0} {1} [{2}] "{3}"' -f $Request.clientIP,($Request.user ?? "-"),(Get-Date -Format "yyyy-MM-dd HH:mm:ss"),$Request.URL
    Write-Host $logentry
}

New-PolarisRouteMiddleware -Name "Request Logger" -Scriptblock {
    Log-Request -Request $Request
}

# The renderer function
function Render-Collector (
    [Parameter(Mandatory = $true)][ScriptBlock]$Collector
) {
    $ch = [Channel]::new() # A class from PrometheusExporter
    $ch.AddMetrics($Collector.Invoke())
    [String]$ch
}

# Collector metric descriptors and initial values
$global:invocations = 0
$collection_time_desc = New-MetricDescriptor -Name "pwsh_collection_time" -Type gauge -Help "Last collection time (s)"
$invocations_desc = New-MetricDescriptor -Name "pwsh_number_of_invocations" -Type counter -Help "Number of collections by this instance"
$uptime_desc = New-MetricDescriptor -Name "pwsh_collector_instance_uptime" -Type counter -Help "Exporter instance uptime (s)"
$starttime = Get-Date

# Custom metrics
# Metric 1 - IBM market cap
$vkey = "demo" # alphavantage.co API key
$IBMMarketCapDesc = New-MetricDescriptor -Name "ibm_market_cap" -Type gauge -Help "IBM market capitalisation"
$GetIBMMarketCap = {(Invoke-RestMethod "https://www.alphavantage.co/query?function=OVERVIEW&symbol=IBM&apikey=$vkey" -Verbose).MarketCapitalization}

# Metric 2 - 2D random motion
$global:x = 0
$global:y = 0
$XYDesc = New-MetricDescriptor -Name "traveler_distance" -Type gauge -Help "Distance from (0,0)"
$XYDistance = {
    $global:x += (-1..1 | Get-Random)
    $global:y += (-1..1 | Get-Random)
    [System.Math]::Sqrt($global:x*$global:x+$global:y*$global:y)
}

# The collector function - outputs Metric[]
function collector() {
    @(
        $tick = Get-Date
        New-Metric -MetricDesc $IBMMarketCapDesc -Value (& $GetIBMMarketCap)
        New-Metric -MetricDesc $XYDesc -Value (& $XYDistance)
        $tock = Get-Date
        New-Metric -MetricDesc $collection_time_desc -Value ($tock - $tick).TotalSeconds
        New-Metric -MetricDesc $invocations_desc -Value (++$global:invocations)
        New-Metric -MetricDesc $uptime_desc -Value ([math]::Floor(((Get-Date) - $starttime).TotalSeconds) )
    )
}

# The runtime
$port = $env:PORT ?? 9070
$starttime = Get-Date
$invocationcount = 0

# Not using the exporter's built-in exporter runtime
# $exp = New-PrometheusExporter -Port $port
# Register-Collector -Exporter $exp -Collector $Function:collector
# $exp.Collect()

New-PolarisGetRoute -Path "/hello" -Scriptblock {
    $Response.Send('hello')
}

New-PolarisGetRoute -Path "/metrics" -Scriptblock {
    $body = Render-Collector $Function:collector
    $Response.ContentType = "text/plain; version=0.0.4; charset=utf-8"
    $Response.Send($body)
}

$Polaris = Start-Polaris -Port $port

while ($Polaris.Listener.IsListening) {
    Wait-Event callbackeventbridge.callbackcomplete
}