How can I update ASP.NET Core app over an existing/running site without stopping the web server?

Question

We have an ASP.NET Core site running on our test server that we would like to auto-deploy by XCopy to our IIS web server as we do our current apps, where I already have the site running. I've added a publish profile that packages the site to a "publish-local" directory within the solution. Whenever I try to copy over the existing site, all DLLs are being used by another process, presumably Kestrel, so I am forced to deploy to a sibling directory and re-map IIS to look at the sibling. How does one update a running ASP.NET Core site without having to manually intervene and stop either the Kestrel or IIS web servers?

Answer 1

When running with IIS you can drop a file called app_offline.htm (case sensitive) to your application folder. IIS will stop your application and will serve the contents of the app_offline.html file. Now you can copy your application. Once finished remove the app_offline.htm and IIS will start your app. This is described in the docs and also in my post on running Asp.NET Core apps with IIS.

Answer 2

a little cheat we use is to rename the old files first (something like my.dll.old ), then copy over the new dlls. Then you can either force or wait for an app pool restart.

Answer 3

Usually I take a backup of the existing version. Then I almost simultaneously recycle the app domain (if I'm using iis) and overwrite the entire contents of the root folder. This way the app restarts with the new version of the code. But it has to be super quick or else there can be issues. In case if anything fails backup can be used to restore to original state.

Answer 4

You can switch the physical path of your IIS site/application with PowerShell:

($curPath = Get-WebFilePath -PSPath "IIS:\Sites\www.example.com\MyApp")
if ($curPath -like "*Blue*") {
    Copy-Item -Path "D:\inetpub\wwwroot\MyAppPath\Staging\*" -Destination "D:\inetpub\wwwroot\MyAppPath\Green" -Recurse -Force
    Set-ItemProperty IIS:\Sites\www.example.com\MyApp -name physicalPath -value "D:\inetpub\wwwroot\MyAppPath\Green"
} else {
    Copy-Item -Path "D:\inetpub\wwwroot\MyAppPath\Staging\*" -Destination "D:\inetpub\wwwroot\MyAppPath\Blue" -Recurse -Force
    Set-ItemProperty IIS:\Sites\www.example.com\MyApp -name physicalPath -value "D:\inetpub\wwwroot\MyAppPath\Blue"
}

Use a staging folder to which you copy your new published files. Then, the above script switches between the green and blue folder. You don't have to stop or recycle your app.