There are two available hybrid search solutions: cloud hybrid search (inbound) and hybrid federated search (outbound). Deciding which hybrid scenario to implement can be determined by looking at which deployment users are primarily working in, what content they'll need, how secure the content needs to be and where the content is stored. The biggest decision driver you should keep in mind, outside of regulatory or legal or geopolitical constraints, is your users' experience in viewing the results.
Cloud hybrid search is our first option, where you set up Office 365 to index all of your SharePoint Online content, as well as information and documents in your on-premise SharePoint. When users enter a query in either search center, they receive results from the Office 365 search index, which contains results from both Office 365 content and the on-premise SharePoint, ranked together.
Hybrid federated search for on-premise SharePoint is our other choice and is where our platforms combine results from the search index in SharePoint Server 2013 and the search index in Office 365. When users enter a query in either search center, they receive results from the Office 365 search index and from the SharePoint Server 2013 search index, getting results from both on-premise SharePoint documents and Office 365 content, but separately.
While both options ensure you see the latest search results of your indexed content, they vary as to where the index data is stored and, more importantly, how it's presented to your users.
Using cloud hybrid search allows the results to come back from the Office 365 search index, which displays and ranks results in a single result block. This allows it to calculate relevance ranking and refiners for all results together, regardless of whether the results come from on-premise or Office 365 content.
When using hybrid federated search, a search center query in either platform returns results from both the on-premiseand Office 365 indexes separately, displaying and ranking results in two separate blocks, with order and ranking determined by their original source.
Although a decision on which hybrid choice to make may be driven by security or regulations, you’ll want to ensure you deliver the best end-user experience that meets their needs. For the convenience of users, it may be best to set up hybrid search in the deployment where most users are working. This can possibly prevent them from having to go to the remote deployment to search for content that may have longer query latency, or waiting longer than normal for documents to open that are stored remotely.
Taking all of this into account, for the best user experience in viewing search results, a cloud hybrid search implementation would be the best option for most organizations. This gives your end users unified search results, search relevance ranking and refiners all together, as well as enabling cloud capabilities such as Office Delve across your on-premise content.
Finally, the best reason your IT will like this option is that none of your existing installations of SharePoint have to be upgraded to have enterprise search in the cloud.