prometheus nginx告警规则如何编写

问题：
目前我搭了一个监控是promethus 根据网上提供的文档，目前监控了nginx 不知道如何进行告警，以及告警规则文件是如何写的
prometheus nginx告警规则如何编写
有没有相关的案例

ALERT NginxHighConnections
  IF nginx_http_connections > 1000
  FOR 5m
  LABELS { severity = "warning" }
  ANNOTATIONS {
    summary = "Nginx has high connections",
    description = "Nginx has more than 1000 connections"
  }