Q:

how to connect existing gateway in Data Factory V2 linked service

We have multiple pipelines in Data Factory V1 for each brand for our organization and We have common gateway named “SQLServerGateway” (Self-Hosted) for on-premises SQL Server for all these pipelines which are running well on a scheduled basis.  
Now, we are trying to create a single test pipeline in Data Factory V2 which is doing the same job in Data Factory V1. Hence we are creating Linked Services in Data Factory V2 and we are trying to link existing gateway “SQLServerGateway” in linked services in V2. But we are not able to fetch that gateway (SQLServerGateway) in dropdown while creating new linked service for on-premises SQL Server. 
Due to gateway not populating in the dropdown, we coded the below part in an advanced note.  But we still receive some error while testing the connection. 
Hence we would like to know how to connect the existing gateway in Data Factory V2 linked service. 
{
    "name": "SQLConn_RgTest",
    "properties": {
        "type": "SqlServer",
        "typeProperties": {
            "connectionString": {           
                "type": "SecureString",             
                "value": "Data Source=XXXX;Initial Catalog=XXXX;Integrated Security=False;user id=XXXX;password=XXXX;"
            }
        },
        "connectVia": {
            "referenceName": "SQLServerGateway",
            "type": "SelfHostedIntegrationRuntime"
        }
    }
}

A:

Currently you cannot reuse the V1 gateways in Data Factory V2.
For your scenario, you need to create a new self-hosted IR in Data Factory V2 and install it on another machine to run the test pipeline. You can follow this tutorial to setup the pipeline. And we will support sharing the self-hosted IR across V2 data factories soon.

