在ADF自托管集成运行时中选择主节点的方法可以通过在ARM模板中指定节点类型来实现。以下是一个示例代码：

{
  "type": "Microsoft.DataFactory/factories",
  "name": "",
  "apiVersion": "2018-06-01",
  "location": "",
  "identity": {
    "type": "SystemAssigned"
  },
  "properties": {
    "publicNetworkAccess": "Enabled",
    "gitConfiguration": {
      "type": "FactoryVSTSConfiguration",
      "accountName": "",
      "repositoryName": "",
      "projectName": "",
      "collaborationBranch": ""
    },
    "dataFlowComputeType": "General",
    "dataFlowComputeLocation": "",
    "dataFlowCoreProperties": {
      "computeType": "General",
      "coreCount": 8,
      "timeToLive": "00:15:00"
    },
    "globalParameters": {},
    "publicIpAddresses": {},
    "integrationRuntime": {
      "type": "Managed",
      "description": "ADF Integration Runtime",
      "linkedInfo": {
        "type": "Managed",
        "resourceId": "/subscriptions//resourceGroups//providers/Microsoft.DataFactory/factories//integrationRuntimes/",
        "authorizationType": "RBAC",
        "isDefault": true
      },
      "typeProperties": {
        "computeType": "General",
        "coreCount": 8,
        "timeToLive": "00:15:00"
      },
      "type": "Managed",
      "typeProperties": {
        "computeType": "General",
        "coreCount": 8,
        "timeToLive": "00:15:00"
      }
    }
  },
  "dependsOn": []
}

在上面的示例中，可以通过设置"dataFlowComputeType"，"dataFlowComputeLocation"，"dataFlowCoreProperties"属性来选择主节点。

请注意替换示例代码中的占位符，如"data-factory-name"，"location"，"data-flow-compute-location"，"subscription-id"，"resource-group"，"integration-runtime-name"等，以适应您的实际环境。