Hybrid search is important for SharePoint Online customers. Migration to the cloud is not an overnight exercise and, in fact, many enterprise customers might not move 100 percent of their infrastructure and content to the cloud; instead, they might opt for a perpetual hybrid state. Here are some key objectives of hybrid deployment:
- Reduce operation cost
- Use hybrid to take advantage of advanced cloud functionalities
- Use hybrid as short- and mid-term migration to cloud strategy
Migration from SharePoint on-premises will typically take a long time for enterprise customers. No one will migrate everything to cloud in one shot. Therefore, during migration, some content will definitely live on-premises and some will be migrated to the cloud. If a company is going to be in the “mid” state for an extended period of time, there is a risk that end users will become confused about what content resides where. That is when hybrid comes in to play; users can search for content and get search results irrespective of where the content resides.
The power of search in enhancing the user experience in hybrid scenarios cannot be stressed too highly. It is the key workload that unifies both the on-premises deployment and the Microsoft Office 365 SharePoint Online environment, making it possible for users to discover and access content in either environment, regardless of the location of the end user. As you will see, the experience of the end user depends largely on what is known as the Authentication Topology and the choice of hybrid implementation.
There are four possible deployment strategies for hybrid search:
- Outbound search (most common) - Outbound from the customer’s network (SharePoint onpremises) to SharePoint Online. A user in the corporate network searches from on-premises. There is an outbound request to SharePoint Online to return results. Results from both verticals are shown on the results page.
- Inbound search - Inbound from SharePoint Online to a customer’s network (SharePoint onpremises). A user who is not on the corporate network but signed into SharePoint Online carries out a search. There is an inbound request to the SharePoint on-premises located on the corporate network to return results. Results from both verticals are shown on the results page.
- Two-way search - Search is set up both inbound and outbound, as just described. Both scenarios are supported in that case—whether the user is on-premises on the corporate network, or signed in only to SharePoint Online.
- Cloud Search Service Application - The on-premises Search Service Application is configured to feed the Office 365 search index to provide a true unified search experience for end users. Outbound search is commonly used alongside the Cloud Search Service Application to provide search results to on-premises users.
The first three of these scenarios are based on the Query model, whereby the search results presented to the user are generated by a federation model at query time and displayed as separate “blocks” of results controlled by query rules. Each block contains search results from different search indexes. This type of hybrid search experience is often referred to as classic hybrid search.
The last scenario represents a very different approach, and in this case the user hybrid experience is driven by a Crawl model, whereby all the results presented to the user are generated from a single search index.
To support these hybrid solutions, SharePoint on-premises and Sharepoint Online need to be configured to support Server-to-Server (S2S) authentication. This provides the ability to support identity delegation across environments such as SharePoint on-premises and SharePoint Online, utilizing the OAuth authentication protocol.
In the same way that SharePoint add-ins use OAuth to access SharePoint data, so hybrid search works based on an OAuth layer. The primary goal of hybrid search experiences is for users to be able to find items regardless of where SharePoint, or indeed the user resides; that is, on-premises or online. Hybrid search gives the ability to run a query and get the most relevant results from SharePoint Online and SharePoint on-premises. In the query federation hybrid scenarios in SharePoint Server 2013 and 2016, we use OAuth and Remote SharePoint Index to give a user in one farm the ability to submit a query to another SharePoint farm. Of primary concern when searching for content is that the permissions on crawled objects or Access Control Lists (ACLs) are respected so that the user gets search results that are appropriately security trimmed. To do this, the user identity needs to be refreshed in the remote SharePoint farm. S2S authentication and related communication is a prime requirement for hybrid search to work.
Source: Configuring Microsoft SharePoint Hybrid Capabilities, Jeremy Taylor, Neil Hodgkinson, Manas Biswas