使用Terraform配置Azure App Service Plan自动缩放时无法切换为规则模式

使用Terraform的azurerm_monitor_autoscale_setting资源为Azure App Service Plan创建横向扩展自动缩放规则后，规则已成功创建，但无法通过代码将App Service Plan的缩放模式从「Automatic」切换为「Rule Based」。手动在Azure门户切换后规则可正常生效，但生产环境不允许手动操作，需完全通过Terraform实现该切换。

代码片段如下：

// autoscaling rules:
resource "azurerm_monitor_autoscale_setting" "autoscaling" {
  name = "${var.azurerm_webapp_service_plan}-autoscale"
  resource_group_name = var.rg_name
  location = var.location
  target_resource_id = var.plan_type == "web_app" ? azurerm_service_plan.webapp_svcplan[0].id : azurerm_service_plan.fa_svcplan[0].id
  
  # Autoscaling Profile: Default
  profile {
    // scaling values for lower envs, change these values for Uat & Prod
    name = "defaultProfile"
    capacity {
      default = 1
      minimum = 1
      maximum = 5
    }

    # Scale out when CPU, Memory, or SocketOutboundAll exceed thresholds
    rule {
      metric_trigger {
        metric_name = "CpuPercentage"
        metric_resource_id = var.plan_type == "web_app" ? azurerm_service_plan.webapp_svcplan[0].id : azurerm_service_plan.fa_svcplan[0].id
        operator = "GreaterThan"
        statistic = "Average"
        threshold = 85
        time_grain = "PT1M"
        time_window = "PT5M"
        time_aggregation = "Average"
      }

要通过Terraform将App Service Plan的缩放模式切换为「Rule Based」，需确保azurerm_monitor_autoscale_setting配置完整且正确，关键注意点如下：

• 显式启用自动缩放设置：添加enabled = true配置，确保自动缩放规则处于激活状态
• 补全规则的动作部分：每个rule块必须包含metric_trigger和scale_action，否则规则不完整，无法触发模式切换
• 确保唯一关联：确认目标App Service Plan没有关联其他自动缩放设置（一个资源仅能绑定一个自动缩放设置）

修改后的完整代码示例（补全关键部分）：

resource "azurerm_monitor_autoscale_setting" "autoscaling" {
  name                = "${var.azurerm_webapp_service_plan}-autoscale"
  resource_group_name = var.rg_name
  location            = var.location
  target_resource_id  = var.plan_type == "web_app" ? azurerm_service_plan.webapp_svcplan[0].id : azurerm_service_plan.fa_svcplan[0].id
  enabled             = true // 显式启用自动缩放

  # Autoscaling Profile: Default
  profile {
    name = "defaultProfile"
    capacity {
      default = 1
      minimum = 1
      maximum = 5
    }

    # 扩展规则：CPU超过85%时增加实例
    rule {
      metric_trigger {
        metric_name        = "CpuPercentage"
        metric_resource_id = var.plan_type == "web_app" ? azurerm_service_plan.webapp_svcplan[0].id : azurerm_service_plan.fa_svcplan[0].id
        operator           = "GreaterThan"
        statistic          = "Average"
        threshold          = 85
        time_grain         = "PT1M"
        time_window        = "PT5M"
        time_aggregation   = "Average"
      }

      scale_action {
        direction = "Increase"
        type      = "ChangeCount"
        value     = "1"
        cooldown  = "PT5M"
      }
    }

    # 可添加更多规则（如内存阈值）
    rule {
      metric_trigger {
        metric_name        = "MemoryPercentage"
        metric_resource_id = var.plan_type == "web_app" ? azurerm_service_plan.webapp_svcplan[0].id : azurerm_service_plan.fa_svcplan[0].id
        operator           = "GreaterThan"
        statistic          = "Average"
        threshold          = 80
        time_grain         = "PT1M"
        time_window        = "PT5M"
        time_aggregation   = "Average"
      }

      scale_action {
        direction = "Increase"
        type      = "ChangeCount"
        value     = "1"
        cooldown  = "PT5M"
      }
    }

    # 收缩规则：CPU低于20%时减少实例
    rule {
      metric_trigger {
        metric_name        = "CpuPercentage"
        metric_resource_id = var.plan_type == "web_app" ? azurerm_service_plan.webapp_svcplan[0].id : azurerm_service_plan.fa_svcplan[0].id
        operator           = "LessThan"
        statistic          = "Average"
        threshold          = 20
        time_grain         = "PT1M"
        time_window        = "PT10M"
        time_aggregation   = "Average"
      }

      scale_action {
        direction = "Decrease"
        type      = "ChangeCount"
        value     = "1"
        cooldown  = "PT10M"
      }
    }
  }
}

执行terraform apply后，Terraform会自动将目标App Service Plan的缩放模式切换为「Rule Based」，无需手动操作。

内容的提问来源于stack exchange，提问作者JKP