Each Power BI dataset is associated with a single gateway cluster, which is composed of one or many gateway instances. For example, if a Power BI dataset (.pbix) imports data from both a SQL Server database and an Excel file, the same gateway cluster will be responsible for the import from both sources. Likewise, if hundreds of business users interact with reports based on the same DirectQuery dataset or a Live connection to an on-premises SSAS instance, these user interactions will generate query requests to the same gateway cluster.
Gateway clusters representing multiple gateways (for example, primary and secondary), each of which must be installed on separate machines as per the Hardware and network requirements section, provide both high availability and load balancing. From an availability standpoint, if an individual gateway instance within a cluster is not running, due to a server failure, for example, the data refresh and user query requests from the Power BI service will be routed to the other gateway instance(s) within the cluster. In terms of query performance and scalability, the Power BI service will distribute (load balance) the query requests across the multiple gateway instances within the cluster.
In the following image from the gateway installer application, a new gateway is added to an existing gateway cluster:
In this example, the new gateway (Frontline Gateway Backup) is added to the Frontline Gateway cluster as per the checkbox and Available gateway clusters selection. Note that the Recovery key for the primary gateway instance, which was created when the first gateway instance of the cluster was installed, is required to add a gateway to a cluster. Additionally, be aware that the gateway management portal in the Power BI service only displays the gateway clusters, not the individual gateways within each cluster. Both the gateway clusters and the individual gateways within each cluster can be accessed and managed via PowerShell scripts as per the Managing gateway clusters section.
Before adding a gateway to a cluster, ensure that the new gateway instance will be able to connect to the same data sources configured for the cluster. As described in the Top gateway planning tasks section, the additional gateways added to gateway clusters should also be installed in locations that minimize the distance between the gateway server, the Power BI service tenant, and the data source(s).