在AWS CloudFormation模板中，可以通过定义适当的资源属性以及使用条件和参数来描述针对ElasticSearch节点的CloudWatch告警。以下是一个示例模板，演示如何通过ElasticSearch节点而不是整个ElasticSearch集群来描述告警：

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Parameters": {
    "ElasticSearchClusterName": {
      "Type": "String",
      "Description": "The name of the ElasticSearch cluster"
    },
    "ElasticSearchNodeName": {
      "Type": "String",
      "Description": "The name of the ElasticSearch node"
    }
  },
  "Conditions": {
    "CreateElasticSearchNodeAlarm": {
      "Fn::Not": [
        {
          "Fn::Equals": [
            {
              "Ref": "ElasticSearchNodeName"
            },
            ""
          ]
        }
      ]
    }
  },
  "Resources": {
    "ElasticSearchNodeAlarm": {
      "Type": "AWS::CloudWatch::Alarm",
      "Condition": "CreateElasticSearchNodeAlarm",
      "Properties": {
        "AlarmName": "ElasticSearchNodeAlarm",
        "AlarmDescription": "Alarm for ElasticSearch node",
        "ComparisonOperator": "GreaterThanThreshold",
        "EvaluationPeriods": "1",
        "MetricName": "NodeLevelMetricName",
        "Namespace": "AWS/ES",
        "Period": "60",
        "Threshold": "90",
        "Statistic": "SampleCount",
        "Dimensions": [
          {
            "Name": "ClusterName",
            "Value": {
              "Ref": "ElasticSearchClusterName"
            }
          },
          {
            "Name": "NodeId",
            "Value": {
              "Ref": "ElasticSearchNodeName"
            }
          }
        ]
      }
    }
  }
}

在这个模板中，有两个参数 ElasticSearchClusterName 和 ElasticSearchNodeName，分别用于指定ElasticSearch集群的名称和节点的名称。

然后，通过条件 CreateElasticSearchNodeAlarm 来判断是否创建ElasticSearch节点的CloudWatch告警。如果 ElasticSearchNodeName 参数不为空，则创建告警。

告警的资源类型是 AWS::CloudWatch::Alarm，其中的 Dimensions 属性指定了要监控的ElasticSearch节点。ClusterName 维度使用了 ElasticSearchClusterName 参数的值，NodeId 维度使用了 ElasticSearchNodeName 参数的值。

这样，根据模板中的值创建CloudFormation堆栈时，将会创建一个针对指定ElasticSearch节点的CloudWatch告警。