I needed to do this recently when working with a team to automated releases of several websites.
The team have a fairly common setup. They’ve got more than one web server behind a load balancer, the load balancer calls a keep alive page to see if the servers are behaving and if they fail to respond stops sending them traffic until they’re healthy again.
What I wanted to do was rename the keep alive page, so the box stops getting new traffic, then wait for the existing sessions to complete and finally start updating it.
The second bit is key here, you don’t want customers using the site to get dropped mid-upload or form post.
I set about seeing what could be done with powershell and put together this little sample. It uses the IIS CmdLets to see how many sessions are still active and waits for them to complete before stopping IIS.
Thought it was a neat little sample worth sharing.
EDIT: I realized that the current script only looked at inflight http requests, I’ve put together a more complex script to interrogate the Active ASP Net sessions on a given IIS Website. See second file in the gist below, hopefully useful.
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| #Get the open requests being handled by IIS | |
| $req = Get-WebRequest | |
| while ($req.Count -gt 0) | |
| { | |
| #Wait if there are some | |
| Write-Host "Waiting for request, current inflight: " $req.Count | |
| Start-Sleep -Seconds 2 | |
| #Check again for sessions | |
| $req = Get-WebRequest | |
| } | |
| Write-Host "No Sessions on Box, lets update!" | |
| ## Do your stopping here, iisreset /stop etc |
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| #WaitForSessionsAspNet.ps1 | |
| $ErrorActionPreference = "Stop" | |
| #Used to get active sessions for a given set of app domains | |
| function Get-ActiveConnections | |
| { | |
| Param( | |
| [string[]]$instanceId | |
| ) | |
| if (-not $instanceId) | |
| { | |
| throw "Instance ID required" | |
| } | |
| $results = $instanceId ` | |
| | %{ Get-Counter -Counter "\asp.net applications($_)\sessions active" } ` | |
| | Select -First 1 -ExpandProperty CounterSamples ` | |
| | Measure-Object -Property CookedValue -Sum ` | |
| | Select -ExpandProperty Sum | |
| Write-Host "Aggregated value for active sessions: " $results | |
| return $results | |
| } | |
| #Use to get the InstanceName for App Domains hosted in a particular website. | |
| #N.B Relies on Get-Websites and Get-WebAppDomain commands which require the webadministration module to be installed. | |
| function Get-PerfCounterInstanceNameForSite | |
| { | |
| Param( | |
| [string]$siteName | |
| ) | |
| if (-not $siteName) | |
| { | |
| throw "siteName required" | |
| } | |
| $website = Get-Website | where { $_.Name -eq $siteName } | |
| if ($website.Length -ne 1) | |
| { | |
| throw "Failed to find site" | |
| } | |
| $appDomain = Get-WebAppDomain ` | |
| | where { $_.siteId -eq $website.id } ` | |
| | Select -ExpandProperty id ` | |
| | ForEach-Object { $_ -replace "/", "_" } ` | |
| if ($appDomain.Length -lt 1) | |
| { | |
| Write-Host "App Domain for the site is not running, probably hasn't been hit recently by a request" | |
| return $null | |
| } | |
| return $appDomain | |
| } | |
| #Script starts here | |
| #Get instance names contained in the website. This is an array as one site can contain multiple app domains | |
| $instanceIds = Get-PerfCounterInstanceNameForSite "Default Web Site" | |
| #If there are no app domains for the site stop | |
| if (-not $instanceIds) | |
| { | |
| Write-Host "App Domain isn't running for the site so there are no sessions" | |
| return | |
| } | |
| #Get the number of active sessions for those app domain instances | |
| $numberOfActiveSess = Get-ActiveConnections $instanceIds | |
| #Loop while still active | |
| while ($numberOfActiveSess -gt 0) | |
| { | |
| #Wait | |
| Write-Host "Waiting for request, current inflight: " $numberOfActiveSess | |
| Start-Sleep -Seconds 10 | |
| #Update to see if session count has dropped | |
| $numberOfActiveSess = Get-ActiveConnections $instanceIds | |
| } | |
| Write-Host "Requests Drained from Machine" |
GripDev 
One response to “Gracefully Drain Session from IIS Before Restarting/Stopping”
Great, thanks. Just what I needed to know to do a safe stop of IIS 🙂