Azure synapse linked service for Azure Function in Terraform

I'm writing a terraform script to create a azure synapse workspace. I've created a linked service for Azure Function but I'm unable to use it in pipeline, where it gives me an error of missing function key.

This is what i'm using now. I'm sure the problem is in the type_properties_json parameter.

resource "azurerm_synapse_linked_service" "FunctionName" {
  name                 = "FunctionName"
  synapse_workspace_id = azurerm_synapse_workspace.synapse.id
  type                 = "AzureFunction"
  type_properties_json = <<JSON
    {
      "functionAppUrl": "https://${data.azurerm_function_app.FunctionName.default_hostname}",
      "authentication": "Anonymous",
      "functionKey": "${data.azurerm_function_app_host_keys.FunctionName.default_function_key}"
    }
  JSON
  depends_on = [
    azurerm_synapse_firewall_rule.allowAll,
    data.azurerm_function_app.FunctionName,
    data.azurerm_function_app_host_keys.FunctionName
  ]
}

And this does create a linked service but when i use it in a pipeline, the run fails with the error

Azure function activity missing function key.

It appears to me after checking the output for azurerm_function_app there is no export for connectionString.

I tried to reproduce the scenario in my environment.

Tried below code:

resource "azurerm_synapse_linked_service" "example" {
  name                 = "kavya-fnapplinked"
  synapse_workspace_id = azurerm_synapse_workspace.example.id
  type                 = "AzureFunction"
  type_properties_json = <<JSON
    {
      "functionAppUrl": "https://${data.azurerm_function_app.example.default_hostname}",
      "authentication": "Anonymous",
     "functionKey": "${data.azurerm_function_app_host_keys.example.default_function_key}"
}
JSON
depends_on = [
    azurerm_synapse_firewall_rule.allowAll,
    data.azurerm_function_app.example,
    data.azurerm_function_app_host_keys.example
  ]

}

Got errors due to the json property and function key not being generated as expected as they are not in correct format.

For this ,note two important points:

1. Function key is only generated after the function app is created first and is a sensitive value.
2. Json format for sensitive values must be in below format

"secret": 
                 {
                "type": "SecureString",
                "value":  “{value}"
               }

• I have first stored the function key in keyvalut , so that it takes time to generate and get stored in secret.

Code:

resource "azurerm_role_assignment" "role_assignment" {
  scope                = azurerm_storage_account.stfn.id
  role_definition_name = "Storage Blob Data Owner"
  principal_id         = data.azurerm_client_config.current.object_id
}

# used Sleep to wait for role assignment to take its time to propagate
resource "time_sleep" "role_assignment_sleep" {
  create_duration = "60s"

  triggers = {
    role_assignment = azurerm_role_assignment.role_assignment.id
  }
}


resource "azurerm_storage_data_lake_gen2_filesystem" "example" {
  name               = "kavdatalakexample123"
  storage_account_id = azurerm_storage_account.stfn.id
   depends_on         = [time_sleep.role_assignment_sleep]
}

resource "azurerm_synapse_workspace" "example" {
  name                = "exmple-workspace"
  resource_group_name = data.azurerm_resource_group.example.name
  location            = data.azurerm_storage_account.example.location
  storage_data_lake_gen2_filesystem_id = azurerm_storage_data_lake_gen2_filesystem.example.id
  sql_administrator_login              = "sqladminuser"
  sql_administrator_login_password     = "H@Sh1CoR3!"
  managed_virtual_network_enabled      = true
  identity {
    type = "SystemAssigned"
  }

}



resource "azurerm_synapse_firewall_rule" "allowAll" {
  name                 = "allowAll"
  synapse_workspace_id = azurerm_synapse_workspace.example.id
  start_ip_address     = "0.0.0.0"
  end_ip_address       = "255.255.255.255"
}


resource "azurerm_storage_account" "stfn" {
  name                     = "kaexpleaccforfunct"
   resource_group_name = data.azurerm_resource_group.example.name
  location            = data.azurerm_storage_account.example.location
  account_tier             = "Standard"
  account_replication_type = "LRS"
}


resource "azurerm_app_service_plan" "example" {
  name                = "exm-kavya-app-service-plan"
  resource_group_name = data.azurerm_resource_group.example.name
  location            =data.azurerm_storage_account.example.location
  kind                = "FunctionApp"
  sku {
    tier = "Dynamic"
    size = "Y1"
  }
}
resource "azurerm_function_app" "example" {
  name                      = "exm-kavya-function-app"
  resource_group_name = data.azurerm_resource_group.example.name
  location            = data.azurerm_resource_group.example.location
 // storage_connection_string = azurerm_storage_account.stfn.primary_connection_string
  storage_account_name       = azurerm_storage_account.stfn.name
  storage_account_access_key = azurerm_storage_account.stfn.primary_access_key
  app_service_plan_id       = azurerm_app_service_plan.example.id
}




data "azurerm_function_app_host_keys" "example" {
 resource_group_name = data.azurerm_resource_group.example.name
 name= azurerm_function_app.example.name
  
}

output "function_key" {
  value = data.azurerm_function_app_host_keys.example.default_function_key
   sensitive = true
}

output "function_appurl" {
  value = "https://${azurerm_function_app.example.default_hostname}"
}



resource "azurerm_key_vault" "example" {
  name                        = "kavyaexamplekeyvault"
  location                    = data.azurerm_resource_group.example.location
  resource_group_name         = data.azurerm_resource_group.example.name
  enabled_for_disk_encryption = true
  tenant_id                   = data.azurerm_client_config.current.tenant_id
  soft_delete_retention_days  = 7
  purge_protection_enabled    = false

  sku_name = "standard"

  access_policy {
    tenant_id = data.azurerm_client_config.current.tenant_id
    object_id = data.azurerm_client_config.current.object_id

   
    key_permissions = [
      "Create",
      "Get",
    ]

    secret_permissions = [
      "Set",
      "Get",
      "Delete",
      "Purge",
      "Recover",
      "List"
    ]

    storage_permissions = [
      "Get","Set"
    ]
  }
}

resource "azurerm_key_vault_secret" "example" {
  name         = "functionkey"
  value        = data.azurerm_function_app_host_keys.example.default_function_key
  key_vault_id = azurerm_key_vault.example.id
}

resource "azurerm_synapse_linked_service" "example" {
  name                 = "kav-fnapplinked"
  synapse_workspace_id = azurerm_synapse_workspace.example.id
  type                 = "AzureFunction"
  type_properties_json = <<JSON
    {
       
  "functionAppUrl": "https://${azurerm_function_app.example.default_hostname}",
  "authentication": "Anonymous",
  "functionKey": 
             {
            "type": "SecureString",
            "value":  "${azurerm_key_vault_secret.example.value}"
           }
      "authentication": "Anonymous",
      "functionKey": 
                 {
                "type": "SecureString",
                "value":  "${azurerm_key_vault_secret.example.value}"
               }
}
JSON

depends_on = [
    azurerm_synapse_firewall_rule.allowAll,
    azurerm_function_app.example,
    data.azurerm_function_app_host_keys.example
  ]

}

With abovecode I could successfully, create linked service.

Linked service for azure synapse workspace:

Reference: azure - Terraform issue creating the resource "azurerm_synapse_linked_service" specifically with the "type_properties_json" field - Stack Overflow