如何在Terraform资源中实现可选的warning块？

错误原因 #

你之前的写法错在在count表达式里引用了count.index——count是用来计算资源实例数量的，此时count.index还未生成，自然会触发报错。

最优实现：用动态块（Dynamic Block） #

没必要拆成两个资源，Terraform的动态块能帮你根据warning_enabled的值决定要不要生成warning块，用单个资源就能搞定需求。

修改后的完整代码：

resource "newrelic_nrql_alert_condition" "additional_alerts_condition" {
  count = length(var.additional_alerts)

  account_id = var.newrelic_account_id
  policy_id  = newrelic_alert_policy.policy.id

  name        = format("%s-%s", local.container_name, var.additional_alerts[count.index].name_suffix)
  type        = "static"
  runbook_url = var.runbook_url
  enabled     = var.additional_alerts[count.index].enabled

  # 动态生成warning块：只有warning_enabled为true时才创建
  dynamic "warning" {
    for_each = var.additional_alerts[count.index].warning_enabled ? [1] : []
    content {
      operator              = var.additional_alerts[count.index].operator
      threshold             = var.additional_alerts[count.index].warning_threshold
      threshold_duration    = var.additional_alerts[count.index].duration
      threshold_occurrences = var.additional_alerts[count.index].occurrences # 注意：原代码里拼错了，是occurrences不是occurences
    }
  }

  critical {
    operator              = var.additional_alerts[count.index].operator
    threshold             = var.additional_alerts[count.index].critical_threshold
    threshold_duration    = var.additional_alerts[count.index].duration
    threshold_occurrences = var.additional_alerts[count.index].occurrences
  }

  nrql {
    query = var.additional_alerts[count.index].query
  }

  aggregation_window = 60
  aggregation_method = "event_flow"
  aggregation_delay  = 120

  slide_by                     = 30
  violation_time_limit_seconds = 3600
}

代码说明 #

• dynamic "warning" 用for_each控制生成逻辑：当warning_enabled为true时，传一个单元素列表[1]，就生成一个warning块；为false时传空列表，直接跳过该块。
• 顺便修正了原代码里的拼写错误：occurences改成occurrences，免得后续出现配置问题。

替代方案：拆分列表（不推荐） #

如果非要拆成两个资源，得先把原列表过滤成两个子列表，再用子列表长度作为count值：

# 先把原列表分成带warning和不带warning的两组
locals {
  alerts_with_warning    = [for alert in var.additional_alerts : alert if alert.warning_enabled]
  alerts_without_warning = [for alert in var.additional_alerts : alert if !alert.warning_enabled]
}

# 生成带warning的告警资源
resource "newrelic_nrql_alert_condition" "with_warning" {
  count = length(local.alerts_with_warning)

  account_id = var.newrelic_account_id
  policy_id  = newrelic_alert_policy.policy.id

  name        = format("%s-%s", local.container_name, local.alerts_with_warning[count.index].name_suffix)
  type        = "static"
  runbook_url = var.runbook_url
  enabled     = local.alerts_with_warning[count.index].enabled

  warning {
    operator              = local.alerts_with_warning[count.index].operator
    threshold             = local.alerts_with_warning[count.index].warning_threshold
    threshold_duration    = local.alerts_with_warning[count.index].duration
    threshold_occurrences = local.alerts_with_warning[count.index].occurrences
  }

  critical {
    operator              = local.alerts_with_warning[count.index].operator
    threshold             = local.alerts_with_warning[count.index].critical_threshold
    threshold_duration    = local.alerts_with_warning[count.index].duration
    threshold_occurrences = local.alerts_with_warning[count.index].occurrences
  }

  nrql {
    query = local.alerts_with_warning[count.index].query
  }

  aggregation_window = 60
  aggregation_method = "event_flow"
  aggregation_delay  = 120

  slide_by                     = 30
  violation_time_limit_seconds = 3600
}

# 生成不带warning的告警资源
resource "newrelic_nrql_alert_condition" "without_warning" {
  count = length(local.alerts_without_warning)

  account_id = var.newrelic_account_id
  policy_id  = newrelic_alert_policy.policy.id

  name        = format("%s-%s", local.container_name, local.alerts_without_warning[count.index].name_suffix)
  type        = "static"
  runbook_url = var.runbook_url
  enabled     = local.alerts_without_warning[count.index].enabled

  critical {
    operator              = local.alerts_without_warning[count.index].operator
    threshold             = local.alerts_without_warning[count.index].critical_threshold
    threshold_duration    = local.alerts_without_warning[count.index].duration
    threshold_occurrences = local.alerts_without_warning[count.index].occurrences
  }

  nrql {
    query = local.alerts_without_warning[count.index].query
  }

  aggregation_window = 60
  aggregation_method = "event_flow"
  aggregation_delay  = 120

  slide_by                     = 30
  violation_time_limit_seconds = 3600
}

但这种写法会导致大量代码重复，维护成本高，所以优先推荐动态块的实现方案。

内容的提问来源于stack exchange，提问作者Aleksey Kurkov