Terraform：为通过弹性豆茎生成的弹性负载平衡器添加cloudwatch警报

Question

我正在为设置ELB的Elastic Beanstalk应用程序设置Terraform配置。我们想要一个在ELB获得太多5XX错误时触发的云监视器警报。我正在尝试从EB环境中传递ELB ARN，但它失败并显示以下消息：

value of 'count' cannot be computed

我知道这是Terraform的一个常见问题，例如https://github.com/hashicorp/terraform/issues/10857我无法找到解决方法。我们正在努力使这款ELB云观察模块通用，因此我无法真正硬编码ELB的数量。

这是我正在使用的代码：

locals {
  elb_count = "${length(var.load_balancer_arns)}"
}

resource aws_cloudwatch_metric_alarm "panic_time" {
  count = "${local.elb_count}"
  alarm_name          = "${var.application_name}-panic-time"
  comparison_operator = "GreaterThanThreshold"
  evaluation_periods  = "1"
  metric_name         = "HTTPCode_ELB_5XX_Count"
  namespace           = "AWS/ELB"
  period              = "60"
  statistic           = "Sum"
  threshold           = "${var.max_5xx_errors}"

  dimensions {
    LoadBalancer = "${element(var.load_balancer_arns, count.index)}"
  }

  alarm_description = "SNS if we start getting a lot of 500 errors"

  alarm_actions = ["${aws_sns_topic.panic_time.arn}"]
}

resource aws_sns_topic "panic_time" {
  name = "${var.application_name}-panic-time"
}

resource aws_sns_topic_policy "panic_time" {
  arn    = "${aws_sns_topic.panic_time.arn}"
  policy = "${data.aws_iam_policy_document.panic_time_sns.json}"
}

data aws_iam_policy_document "panic_time_sns" {
  statement {
    actions = [
      "SNS:Publish",
    ]

    resources = [
      "${aws_sns_topic.panic_time.arn}",
    ]

    principals {
      type        = "Service"
      identifiers = ["events.amazonaws.com"]
    }
  }
}

我从main.tf中的环境传递负载均衡器：

load_balancer_arns = "${module.environment.load_balancers}"

（load_balancers输出看起来像这样:)

output load_balancers {
  value = "${aws_elastic_beanstalk_environment.main.load_balancers}"
}

Answer 1

没有得到每个环境有多少个ELB。我为每个环境使用了一个ELB的解决方法：

resource "aws_elastic_beanstalk_environment" "some-environment" {
 count = "${length(var.environments)}"
 ...
}

resource "aws_cloudwatch_metric_alarm" "alarm-unhealthy-host-count" {
 count = "${length(var.environments)}"
 ...

 dimensions {
  LoadBalancerName = "${element(aws_elastic_beanstalk_environment.some-environment.*.load_balancers[count.index], 0)}"
 }
}

这很有趣，但我可以将任何值传递给元素（...，val），并且每次我获得每个环境唯一正确的ELB名称。