ARM template for a web app with variable slots

webapp-with-variable-slots.json

{
    "$schema": "http://schema.management.azure.com/schemas/2014-04-01-preview/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
        "webAppName": {
            "type": "string"
        },
        "webAppSKU": {
            "type": "string",
            "defaultValue": "F1",
            "allowedValues": [
                "F1",
                "D1",
                "B1",
                "B2",
                "B3",
                "S1",
                "S2",
                "S3",
                "P1",
                "P2",
                "P3",
                "P1V2",
                "P2V2",
                "P3V2"
            ]
        },
        "location": {
            "type": "string",
            "defaultValue": "[resourceGroup().location]"
        },
        "hostingPlanName": {
            "type": "string",
            "defaultValue": "[concat(parameters('webAppName'),'-plan', uniqueString(resourceGroup().name))]"
        },
        "numberWorkers": {
            "type": "int",
            "defaultValue": 1
        },
        "slotNumberWorkers": {
            "type": "int",
            "defaultValue": 1
        },
        "alwaysOn": {
            "type": "bool",
            "defaultValue": true
        },
        "httpsOnly": {
            "type": "bool",
            "defaultValue": true
        },
        "slots": {
            "type": "array",
            "defaultValue": []
        }
    },
    "variables": {
        "internalSlots": "[if(equals(0, length(parameters('slots'))) , createArray('__dummy')  , parameters('slots') )]"

    },
    "resources": [
        {
            "name": "[parameters('webAppName')]",
            "type": "Microsoft.Web/sites",
            "apiVersion": "2018-02-01",
            "location": "[parameters('location')]",
            "properties": {
                "serverFarmId": "[resourceId('Microsoft.Web/serverfarms', parameters('hostingPlanName'))]",
                "numberWorkers": "[parameters('numberWorkers')]",
                "siteConfig": {
                    "httpsOnly": "[parameters('httpsOnly')]",
                    "appSettings": [],
                    "connectionStrings": []
                },
                "alwaysOn": "[parameters('alwaysOn')]"
            },
            "dependsOn": [
                "[parameters('hostingPlanName')]"
            ]
        },
        {
            "condition": "[not(equals('__dummy', variables('internalSlots')[copyIndex()]))]",
            "name": "[concat(parameters('webAppName'), '/', variables('internalSlots')[copyIndex()])]",
            "type": "Microsoft.Web/sites/slots",
            "apiVersion": "2018-02-01",
            "location": "[parameters('location')]",
            "properties": {
                "serverFarmId": "[resourceId('Microsoft.Web/serverfarms', parameters('hostingPlanName'))]",
                "numberWorkers": "[parameters('slotNumberWorkers')]",
                "siteConfig": {
                    "httpsOnly": "[parameters('httpsOnly')]",
                    "appSettings": [],
                    "connectionStrings": []
                },
                "alwaysOn": "[parameters('alwaysOn')]"
            },

            "copy": {
                "name": "slotIndex", 
                "count": "[length(variables('internalSlots'))]" 
            },

            "dependsOn": [
                "[parameters('hostingPlanName')]",
                "[parameters('webAppName')]"
            ]
        },
        {
            "type": "Microsoft.Web/serverfarms",
            "apiVersion": "2018-02-01",
            "name": "[parameters('hostingPlanName')]",
            "location": "[parameters('location')]",
            "sku": {
                "name": "[parameters('webAppSKU')]"
            }
        }
    ]
}