policy

{
    "properties": {
        "policyType": "Custom",
        "mode": "All",
        "parameters": {
            "logAnalyticsEurope": {
                "type": "string",
                "metadata": {
                    "displayName": "Log Analyitcs workspace in Europe",
                    "description": "Select the Log Analytics workspace from dropdown list",
                    "strongType": "omsWorkspace"
                }
            },
            "logAnalyticsAmerica": {
                "type": "string",
                "metadata": {
                    "displayName": "Log Analytics workspace in America",
                    "description": "Select the Log Analytics workspace from dropdown list",
                    "strongType": "omsWorkspace"
                }
            }
        },
        "policyRule": {
            "if": {
                "field": "type",
                "equals": "Microsoft.Network/networkSecurityGroups"
            },
            "then": {
                "effect": "deployIfNotExists",
                "details": {
                    "type": "Microsoft.Insights/diagnosticSettings",
                    "name": "setByPolicy",
                    "existenceCondition": {
                        "allOf": [
                            {
                                "field": "Microsoft.Insights/diagnosticSettings/logs.enabled",
                                "equals": "true"
                            },
                            {
                                "field": "Microsoft.Insights/diagnosticSettings/workspaceId",
                                "in": [
                                    "[parameters('logAnalyticsEurope')]",
                                    "[parameters('logAnalyticsAmerica')]"
                                ]
                            }
                        ]
                    },
                    "deployment": {
                        "properties": {
                            "parameters": {
                                "logAnalyticsEurope": {
                                    "value": "[parameters('logAnalyticsEurope')]"
                                },
                                "logAnalyticsAmerica": {
                                    "value": "[parameters('logAnalyticsAmerica')]"
                                },
                                "location": {
                                    "value": "[field('location')]"
                                },
                                "nsgName": {
                                    "value": "[field('name')]"
                                }
                            },
                            "mode": "incremental",
                            "template": {
                                "$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
                                "contentVersion": "1.0.0.0",
                                "parameters": {
                                    "nsgName": {
                                        "type": "string"
                                    },
                                    "logAnalyticsEurope": {
                                        "type": "string"
                                    },
                                    "logAnalyticsAmerica": {
                                        "type": "string"
                                    },
                                    "location": {
                                        "type": "string"
                                    }
                                },
                                "variables": {},
                                "resources": [
                                    {
                                        "condition": "[equals(parameters('location'), 'northeurope')]",
                                        "type": "Microsoft.Network/networkSecurityGroups/providers/diagnosticSettings",
                                        "apiVersion": "2017-05-01-preview",
                                        "name": "[concat(parameters('nsgName'), '/', 'Microsoft.Insights/setByPolicyEU')]",
                                        "location": "[parameters('location')]",
                                        "dependsOn": [],
                                        "properties": {
                                            "workspaceId": "[parameters('logAnalyticsEurope')]",
                                            "logs": [
                                                {
                                                    "category": "NetworkSecurityGroupEvent",
                                                    "enabled": true
                                                },
                                                {
                                                    "category": "NetworkSecurityGroupRuleCounter",
                                                    "enabled": true
                                                }
                                            ]
                                        }
                                    },
                                    {
                                        "condition": "[equals(parameters('location'), 'eastus')]",
                                        "type": "Microsoft.Network/networkSecurityGroups/providers/diagnosticSettings",
                                        "apiVersion": "2017-05-01-preview",
                                        "name": "[concat(parameters('nsgName'), '/', 'Microsoft.Insights/setByPolicyUS')]",
                                        "location": "[parameters('location')]",
                                        "dependsOn": [],
                                        "properties": {
                                            "workspaceId": "[parameters('logAnalyticsAmerica')]",
                                            "logs": [
                                                {
                                                    "category": "NetworkSecurityGroupEvent",
                                                    "enabled": true
                                                },
                                                {
                                                    "category": "NetworkSecurityGroupRuleCounter",
                                                    "enabled": true
                                                }
                                            ]
                                        }
                                    }
                                ],
                                "outputs": {}
                            }
                        }
                    },
                    "roleDefinitionIds": [
                        "/providers/Microsoft.Authorization/roleDefinitions/b24988ac-6180-42a0-ab88-20f7382dd24c"
                    ]
                }
            }
        }
    }
}