Azure Function ARM template with Staging and Production slots.

azure-function-arm-template-with-staging-slot.json

{
  "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "azureSubscriptionId": {
        "type": "string",
        "metadata": {
          "description": "The azure subscription Id. Something like 12345678-abcd-abcd-abcd-1234567890ab."
        }
    },
    "appName": {
      "type": "string",
      "metadata": {
        "description": "The name of the Function app to be created / modified"
      }
    },
    "appServicePlanName": {
      "type": "string",
      "metadata": {
        "description": "The name of the App Service plan that will host the Function app - this must exist already."
      }
    },
    "functionsStorageAccountName": {
      "type": "string",
      "metadata": {
        "description": "The name of the storage account to be created / modified that will be used to power the new Function app.  More details in the comment of the resource."
      }
    },
    "websiteStorageAccountName": {
      "type": "string",
      "metadata": {
        "description": "The name of the existing storage account that the website uses as it's primary storage account (e.g. for queues and table storage)."
      }
    },
    "applicationInsightsName": {
      "type": "string",
      "metadata": {
        "description": "The name of the existing application insight to log information."
      }
    },
    "applicationInsightsLocation": {
      "type": "string",
      "metadata": {
        "description": "The name of the existing application insight to log information."
      }
    }
  },
  "variables": {
    "functionsStorageAccountid": "[concat('/subscriptions/', parameters('subscriptionId'), '/resourceGroups/', resourceGroup().name, '/providers/Microsoft.Storage/storageAccounts/', parameters('functionsStorageAccountName'))]",
    "websiteStorageAccountid": "[concat('/subscriptions/', parameters('subscriptionId'), '/resourceGroups/', resourceGroup().name, '/providers/Microsoft.Storage/storageAccounts/', parameters('websiteStorageAccountName'))]",
    "slotName": "[concat(parameters('appName'), '/staging')]"
  },
  "resources": [
    {
      "type": "Microsoft.Storage/storageAccounts",
      "name": "[parameters('functionsStorageAccountName')]",
      "apiVersion": "2016-12-01",
      "location": "[resourceGroup().location]",
      "kind": "Storage",
      "sku": {
        "name": "Standard_LRS"
      },
      "properties": {
        "supportsHttpsTrafficOnly": false,
        "encryption": {
          "keySource": "Microsoft.Storage",
          "services": {
            "blob": {
              "enabled": true
            },
            "file": {
              "enabled": true
            }
          }
        },
        "dependsOn": [],
        "comments": "This storage account is used to log to Azure Table storage and power the Monitor tab in the portal. We explicity use a seperate account, in case we want to change the SKU of websiteStorageAcccount parameter."
      }
    },
    {
      "name": "[parameters('applicationInsightsName')]",
      "apiVersion": "2014-04-01",
      "type": "Microsoft.Insights/components",
      "kind": "other",
      "location": "[parameters('applicationInsightsLocation')]",
      "properties": { "applicationId": "[parameters('applicationInsightsName')]" }
    },
    {
      "name": "[parameters('appName')]",
      "apiVersion": "2015-08-01",
      "type": "Microsoft.Web/sites",
      "kind": "functionapp",
      "location": "[resourceGroup().location]",
      "identity": {
        "type": "SystemAssigned"
      },
      "properties": {
        "serverFarmId": "[resourceId('Microsoft.Web/serverfarms', parameters('appServicePlanName'))]",
        "siteConfig": {
          "phpVersion": "off",
          "use32BitWorkerProcess": "false",
          "alwaysOn": "true",
          "remoteDebuggingEnabled": "false",
          "remoteDebuggingVersion": "",
          "webSocketsEnabled": true,
          "http20Enabled": true,
          "ftpsState": "Disabled",
          "appSettings": [
            {
              "name": "FUNCTIONS_EXTENSION_VERSION",
              "value": "~1"
            },
            {
              "name": "Project",
              "value": "src"
            }
          ]
        },
        "dependsOn": [
          "[resourceId('Microsoft.Web/Sites', parameters('appName'))]",
          "[resourceId('Microsoft.Storage/storageAccounts', parameters('functionsStorageAccountName'))]",
          "[resourceId('Microsoft.Insights/components', parameters('applicationInsightsName'))]"
        ],
        "comments": "This Function App will host all Azure functions."
      },
      "resources": [
        {
          "name": "slotConfigNames",
          "type": "config",
          "apiVersion": "2015-08-01",
          "dependsOn": [
            "[resourceId('Microsoft.Web/Sites', parameters('appName'))]"
          ],
          "tags": {
            "displayName": "slotConfigNames"
          },
          "properties": {
            "appSettingNames": [
              "DisableAllFunctions"
            ]
          }
        },
        {
          "apiVersion": "2015-08-01",
          "name": "appsettings",
          "type": "config",
          "dependsOn": [
            "[resourceId('Microsoft.Web/Sites', parameters('appName'))]",
            "[resourceId('Microsoft.Storage/storageAccounts', parameters('functionsStorageAccountName'))]"
          ],
          "properties": {
            //Important: when adding new App Setting, you need to add them to the staging slot
            "DisableAllFunctions": "false", //note this setting is slot specific
            "AzureWebJobsStorage": "[concat('DefaultEndpointsProtocol=https;AccountName=', parameters('websiteStorageAccountName'), ';AccountKey=', listKeys(variables('websiteStorageAccountid'),'2015-05-01-preview').key1)]",
            "AzureWebJobsDashboard": "[concat('DefaultEndpointsProtocol=https;AccountName=', parameters('functionsStorageAccountName'), ';AccountKey=', listKeys(variables('functionsStorageAccountid'),'2015-05-01-preview').key1)]",
            "FUNCTIONS_EXTENSION_VERSION": "~1",
            "APPINSIGHTS_INSTRUMENTATIONKEY": "[reference(resourceId('Microsoft.Insights/components', parameters('applicationInsightsName')), '2014-04-01').InstrumentationKey]"
          }
        }
      ]
    },
    {
      "apiVersion": "2016-08-01",
      "dependsOn": [
        "[resourceId('Microsoft.Web/sites', parameters('appName'))]"
      ],
      "kind": "functionapp",
      "location": "[resourceGroup().location]",
      "name": "[variables('slotName')]",
      "properties": {
        "enabled": true,
        "serverFarmId": "[resourceId('Microsoft.Web/serverfarms', parameters('appServicePlanName'))]"
      },
      "type": "Microsoft.Web/sites/slots",
      "resources": [
        {
          "name": "appsettings",
          "type": "config",
          "apiVersion": "2015-08-01",
          "dependsOn": [
            "[resourceId('Microsoft.Web/sites/slots', variables('slotName'))]"
          ],
          "tags": {
            "displayName": "AppSettings"
          },
          "properties": {
            //Important: when adding new App Setting, you need to add them to the production slot
            "DisableAllFunctions": "true", //note this setting is slot specifc
            "AzureWebJobsStorage": "[concat('DefaultEndpointsProtocol=https;AccountName=', parameters('websiteStorageAccountName'), ';AccountKey=', listKeys(variables('websiteStorageAccountid'),'2015-05-01-preview').key1)]",
            "AzureWebJobsDashboard": "[concat('DefaultEndpointsProtocol=https;AccountName=', parameters('functionsStorageAccountName'), ';AccountKey=', listKeys(variables('functionsStorageAccountid'),'2015-05-01-preview').key1)]",
            "FUNCTIONS_EXTENSION_VERSION": "~1",
            "APPINSIGHTS_INSTRUMENTATIONKEY": "[reference(resourceId('Microsoft.Insights/components', parameters('applicationInsightsName')), '2014-04-01').InstrumentationKey]"
          }
        }
      ]
    }
  ]
}

From line 89-161 it appears that you're deploying a function app with two resources. One of those resource has the type "config" and name "slotConfigNames", on lines 127-142. Lines 143-159 appear to already configure the properties. What is the purpose of this resource being defined?

I'm not sure if I fully understand your question, but here is what each each groups of line objective:
Line 89-96 is the Function App (a type of App Service).
Line 97-118 are the Function App's properties
Lines 128-142 is the Function Apps slot configuration
Lines 143-159 is the Function App's app settings

Lines 162-196 deploy the staging slot for the function app. This resource deployment doesn't have the same resource defined like in the production slot on lines 127-142.

Yes - the point is to keep the production slot online.. This is explained in my related blog post https://andypalmer.dev/posts/automated-deployment-of-azure-functions-arm-templates/

Another question...couldn't you just embed the resource defined on lines 162-196 under the existing "resources" array in the production app? According to the schema documentation for the Sites template, you can provide a "slot" resource in the Microsoft.Web/sites object.

This sounds like it could work.