A Linked Service in Azure Data Factory (ADF) is a reference to a data store or a compute service. Think of it as a connection string that ADF uses to securely connect to external resources. Linked Services are essential for specifying how ADF should connect to various sources and destinations of data, as well as computing environments for data processing.

What is ADF Linked Service?

Definition: Linked service defines the connection information to a data store or Azure compute service.

• ADF primarily is an ETL (Extract, Transform, Load) tool (Extract, Transform and Load). So obviously, we need to connect to data sources to work on it.
• The activities in the ADF pipeline are the actions to be performed on your data. But the question is how do we connect to the data source from the ADF pipeline? The answer is using ADF Linked Service.
• A few examples:
  • Example 1: You want to copy some files from SharePoint to Azure BLOB storage. In this case you will require two separate Linked Services. One to connect with SharePoint database (Your Source) and one to connect to Azure BLOB Storage (your destination).
  • Example 2: You want to execute a stored procedure on Azure SQL Database. To connect to Azure SQL DB, you need to create an ADF Linked Service.

How to implement parameterized Linked Service in ADF?

• You can have parameters in the linked service so that when you use them in your dataset, you can use dynamic values.
• It is recommended not to parameterize the username, password or any other such sensitive information.
• There is an open bug to use "-" in parameter names, it is recommended to use names without "-" until the bug is resolved.
• Example:
  • Here, we have created an HTTP Linked Service for SharePoint connection. Using this we are trying to get to the file residing in a SharePoint document library.
  • Now we are going to pass two parameters here. As you can see in the screenshot, we can also provide the default values.
    • FileName
    • FilePath
      
    • We will now open the dataset where we have used this Linked Service. In the connection tab, you can expand the parameters option. As shown in the screenshot, the two parameters’ values are provided dynamically using the pipeline variables.
      

Example 1: How to create an ADF Linked service to Azure SQL?

• Go to Azure Portal
• Go to your ADF resource.
• From the top left section, click on Manage.
  
• Now, click on New and then search for Azure SQL Database. Select the Data store and click on continue
  
• Configure the connection details.
  
  • Name: Give a meaningful name to your Linked Service.
  • Description: Describe your Linked service in a few understandable words.
  • Connect via integration runtime: The Integration Runtime (IR) is the compute infrastructure used by the Data Factory to provide data integration capabilities across different network environments. Azure Integration Runtime can be used to connect to data stores and compute services in public networks with publicly accessible endpoints. Use a self-hosted Integration Runtime for private/on-premises networks.

There are two options to connect now.

1. Connection String: In connection string also, there are two options for account selection method
   1. Account Selection method: Select from a list of available Azure SQL servers and databases in your Azure subscriptions or enter server name and database name manually.
      1. From Azure Subscription: Enter the details manually.
         
         1. Azure Subscription: All the subscription will be listed in the dropdown; you need to choose the appropriate one.
         2. Server name: Enter your server name.
         3. Database name: find this out from the Azure SQL DB connection string.
         4. Authentication type: there are four types of authentication types, choose one and accordingly enter the details.
            1. SQL Authentication: If you know the ID and Password, you can choose SQL Authentication.
            2. System Assigned Managed Identity: Grant Data Factory service managed identity access to your Azure SQL Database
            3. Service Principal: For this authentication, along with general properties you need to specify a few things like, ServicePrincipalId, ServicePrincipalKey, tenant. For more details, refer this.
            4. User Assigned Managed Identity: You need to provide credentials for this type of identity. Reference.
            
            
            5. Enter Manually: Enter all the details below manually.
               
            6. Fully qualified domain name: You can see this value from your Azure SQL Database connection string.
            7. Database name: Again, refer the connection string
            8. Authentication type: There are a few options here.
            9. SQL Authentication: If you know the ID and Password, you can choose SQL Authentication.
            10. System Assigned Managed Identity: Grant Data Factory service managed identity access to your Azure SQL Database
            11. Service Principal: For this authentication, along with general properties you need to specify a few things like, ServicePrincipalId, ServicePrincipalKey, tenant. For more details, refer this.
            12. User Assigned Managed Identity: You need to provide credentials for this type of identity. Reference.
2. After all the details are added you can test the connection from the bottom right corner of the screen.
   .

Example 2: How to create an ADF Linked service to SharePoint Library?

• Now search for SharePoint from the list of databases.
  
• Enter all the required details.
  
  • Name: Enter meaningful name to the Linked service.
  • Description: Describe your linked service in an understandable manner.
  • Site URL: Put the SharePoint Site URL here.
  • Tenant: The tenant ID under which your application resides. You can find it from Azure portal Active Directory overview page.
  • Service Principal ID: The application (client) ID of your application registered in Azure Active Directory. Make sure to grant SharePoint site permission to this application.
  • Service principal key: The client secret of your application registered in Azure Active Directory.