Hi Bil
Octopus does not natively support this (AFAIK), it's an IIS
feature for taking ASP.NET applications offline just by the
presence of the app_offline.htm file in the root directory. There
are is an Octopus Deploy Library template here
https://library.octopusdeploy.com/step-template/actiontemplate-iis-...
if that's what you're referring to?
Or else you could use custom powershell to do this (which is how
I do it), by deploying an app_offline.htm to the current IIS
directory, then Octopus deploys to the new directory and switches
IIS over then your app comes back online.
Gavin