Deploy ACA with zero downtime

deploy-app-revision.ps1

<#
.DESCRIPTION
    deploy-app-revision Creates a new revision of the app, waits for it to be healthy and swaps traffic
#>
Param (
    [String] $Environment = "some-rg",
    [String] $AppName = "some-app",
    [String] $HealthcheckPath = "api/healthcheck",
    [String] $Subscription = "",
    [int] $TimeoutSeconds = 100,
    [int] $PollingIntervalSeconds = 5
)

Write-Host "Reading information from $appName..."

# Get revisions
$revisions = az containerapp revision list -n $appName -g $Environment --subscription $Subscription `
    | ConvertFrom-Json

# Get hostname info
$hostnames = az containerapp show -g $Environment -n $appName --subscription $Subscription `
    --query "properties.[latestRevisionFqdn,latestRevisionName]" `
    | ConvertFrom-Json

# i.e. somethingsomething-ff1921d9.centralus.azurecontainerapps.io
$hostSuffix = ($hostnames[0] -replace $hostnames[1], "").Substring(1)

# Define a health checking function
function Wait-Ready($Revision) {

    # Wait for revision to be ready
    $fqdn = "$Revision.$hostSuffix"
    Write-Host "Invoking https://$fqdn/$HealthcheckPath with $TimeoutSeconds seconds remaining..."

    # Start a stopwatch
    $stopwatch = [system.diagnostics.stopwatch]::StartNew()
    $remaining = $TimeoutSeconds
    $healthy   = $false
    $tries     = 0

    while (-not $healthy -and $remaining -gt 0) {
        $start = $stopwatch.Elapsed.TotalSeconds

        try {
            $timeoutFor = $remaining -gt $PollingIntervalSeconds ? $PollingIntervalSeconds : $remaining
            $response = Invoke-WebRequest -Uri "https://$fqdn/$HealthcheckPath" -UseBasicParsing -Timeout $timeoutFor
            $healthy = $response.StatusCode -eq 200
        }
        catch {
            $tries++
            $end = $stopwatch.Elapsed.TotalSeconds
            $remaining = $TimeoutSeconds - $end

            Write-Host "Revision not ready... (try $tries, $remaining seconds remaining)"
            if ($remaining -gt 0 -and $end - $start -lt $PollingIntervalSeconds) {
                $sleep = $PollingIntervalSeconds - ($end - $start)
                Start-Sleep -Seconds $sleep
            }

            $remaining = $TimeoutSeconds - $stopwatch.Elapsed.TotalSeconds
        }
    }

    return $healthy
}

# Step 1: Set traffic to currently active traffic revision
$active = $revisions | Where-Object { $_.properties.trafficWeight -gt 0 } | Select-Object -First 1
$activeRevName = $active.name

Write-Host "Setting $activeRevName to 100% traffic..."
az containerapp ingress traffic set -n $appName -g $Environment --subscription $Subscription --revision-weight "$activeRevName=100"

# Step 2: Clone latest revision with new suffix
$newId = [guid]::NewGuid().ToString("N").Substring(0, 8)
$revName = "$appName--$newId"

Write-Host "Creating a new revision $revName..."
az containerapp revision copy -n $appName -g $Environment --subscription $Subscription --revision-suffix $newId

# Step 3: Wait for newRevision to be ready
if (Wait-Ready -Revision $revName) {

    # Step 4: Update traffic weights to new revision
    Write-Host "Updating traffic weights..."
    az containerapp ingress traffic set -n $appName -g $Environment --subscription $Subscription --revision-weight "latest=100"

    # Step 5: Deactivate revisions with 0 traffic
    foreach ($rev in $revisions) {
        Write-Host "Deactivating " $rev.name
        az containerapp revision deactivate -n $appName -g $Environment --subscription $Subscription --revision $rev.name
    }
}
else {
    Write-Host "Revision failed to become ready" -ForegroundColor Red

    Exit 1
}