We are preparing a Sitecore upgrade and looking into Azure Search for indexing.
Can anyone tell me if Azure Search can be comined with on premises hosting? Or do you need to host Sitecore in Azure to use Azure search?
Yes, you can use an external index provider by implementing a custom search provider to use in place of the standard Lucene or Solr indexes.
This is made possible by Sitecore providing a number of interfaces and base-classes that developers can extend if they want to create their own provider, allowing you in theory to create any kind of index you like.
This means you can use Azure Search regardless of the fact you are hosting on-premise.
Additionally, in the case of Azure Search, someone has already gone to the trouble of already creating a search provider for it that is compatible with Sitecore 8.1.
The code is hosted here - https://github.com/jscott1277/SitecoreAzureSearchProvider
It is also on the Sitecore Marketplace - https://marketplace.sitecore.net/Modules/S/Sitecore_Azure_Search_Provider.aspx?sc_lang=en
The developer has published two blog posts on the approach they took to creating this:
Future updates of Sitecore XP 8.2 will come with Azure Search provider out of the box and will bring support for content indexes such as