Terraform创建多ALB CloudWatch仪表盘遇for循环重复键错误

尝试为多个ALB（应用负载均衡器）和目标组创建CloudWatch仪表盘时，Terraform的for_each循环因传入重复键值"AWS/ApplicationELB"报错，需要解决重复键问题。

data.tf 配置 #

dashboards = [
  {
    my-dashboard-name = "Cloudwatch-Dashboard-ALB-test3"
    aws-region        = "us-east-1"
    targets           = ["app/test3/e8586bb7d49cf35b"]
    target_groups     = ["targetgroup/test-tg-2/f2e0260797ce83e8","targetgroup/test4/2dd3e8ae3bf2cb94"]
    metrics           = ["RequestCountPerTarget", "NewConnectionCount", "TargetResponseTime", "HTTPCode_Target_2XX_Count","RuleEvaluations", "HTTPCode_ELB_4XX_Count", "HTTPCode_Target_3XX_Count", "HTTP_Redirect_Count", "ActiveConnectionCount", "ProcessedBytes", "HTTPCode_ELB_3XX_Count", "RequestCount", "HTTPCode_ELB_5XX_Count", "HTTPCode_ELB_504_Count", "ConsumedLCUs", "HTTPCode_ELB_503_Count", "HTTPCode_ELB_502_Count", "HTTP_Fixed_Response_Count", "HTTPCode_Target_4XX_Count", "UnHealthyHostCount", "HealthyHostCount"]
    aws-namespace     = "AWS/ApplicationELB"
    dim               = "LoadBalancer"
    service_names      = ""
    stat              = "Average"
    period            = 300
  },
  {
     my-dashboard-name = "Cloudwatch-Dashboard-ALB-test"
     aws-region        = "us-east-1"
     targets           = ["app/test2/eb397187e673ccc3"]
     target_groups     = ["targetgroup/test-tg/62fdb81766299e0e"]
     metrics           = ["RequestCountPerTarget", "NewConnectionCount", "TargetResponseTime", "HTTPCode_Target_2XX_Count","RuleEvaluations", "HTTPCode_ELB_4XX_Count", "HTTPCode_Target_3XX_Count", "HTTP_Redirect_Count", "ActiveConnectionCount", "ProcessedBytes", "HTTPCode_ELB_3XX_Count", "RequestCount", "HTTPCode_ELB_5XX_Count", "HTTPCode_ELB_504_Count", "ConsumedLCUs", "HTTPCode_ELB_503_Count", "HTTPCode_ELB_502_Count", "HTTP_Fixed_Response_Count", "HTTPCode_Target_4XX_Count", "UnHealthyHostCount", "HealthyHostCount"]
     aws-namespace     = "AWS/ApplicationELB"
     dim               = "LoadBalancer"
     service_names      = ""
     stat              = "Average"
     period            = 300
   },
 ]
}

cloudwatch.tf 配置 #

module "create-dashboard" {
  source = "../"
  for_each       = { for service in local.dashboards : service.aws-namespace  => service}
  dashboard-name = each.value.my-dashboard-name
  aws-region     = each.value.aws-region
  targets        = each.value.targets
  metrics        = each.value.metrics
  aws-namespace  = each.value.aws-namespace
  dim            = each.value.dim
  service_names  = each.value.service_names
  target_groups  = each.value.target_groups
  cluster_name   = ["a-cluster"]
  stat           = each.value.stat
  period         = each.value.period
}

错误信息 #

╷
│ Error: Duplicate object key
│
│   on cloudwatch-v1.tf line 10, in module "create-dashboard":
│   10:   for_each       = { for idx, service in local.dashboards : service.aws-namespace  => service}
│     ├────────────────
│     │ service.aws-namespace is "AWS/ApplicationELB"
│
│ Two different items produced the key "AWS/ApplicationELB" in this 'for' expression. If duplicates are expected, use the ellipsis (...) after the value
│ expression to enable grouping by key

报错核心原因是for_each要求映射的键必须唯一，你当前用service.aws-namespace作为键，两个仪表盘的命名空间完全相同，导致键重复。以下是两种可行的解决方法：

方法1：使用仪表盘名称作为唯一键（推荐） #

每个仪表盘的名称本身就是唯一标识，直接用它作为for_each的键：

module "create-dashboard" {
  source = "../"
  for_each       = { for service in local.dashboards : service.my-dashboard-name => service}
  dashboard-name = each.value.my-dashboard-name
  aws-region     = each.value.aws-region
  targets        = each.value.targets
  metrics        = each.value.metrics
  aws-namespace  = each.value.aws-namespace
  dim            = each.value.dim
  service_names  = each.value.service_names
  target_groups  = each.value.target_groups
  cluster_name   = ["a-cluster"]
  stat           = each.value.stat
  period         = each.value.period
}

这种方式直观且符合业务逻辑，每个模块实例对应一个独立的仪表盘。

方法2：使用索引+命名空间组合键 #

如果不想用仪表盘名称，也可以结合列表索引和命名空间生成唯一键：

module "create-dashboard" {
  source = "../"
  for_each       = { for idx, service in local.dashboards : "${service.aws-namespace}-${idx}" => service}
  dashboard-name = each.value.my-dashboard-name
  aws-region     = each.value.aws-region
  targets        = each.value.targets
  metrics        = each.value.metrics
  aws-namespace  = each.value.aws-namespace
  dim            = each.value.dim
  service_names  = each.value.service_names
  target_groups  = each.value.target_groups
  cluster_name   = ["a-cluster"]
  stat           = each.value.stat
  period         = each.value.period
}

索引从0开始，生成的键类似AWS/ApplicationELB-0、AWS/ApplicationELB-1，确保每个键唯一。

注意事项 #

错误提示中提到的...语法是用来将重复键的多个值分组到同一个键下，比如{ for service in local.dashboards : service.aws-namespace => service... }，但这会把两个仪表盘的配置合并到一个模块实例中，不符合你创建多个独立仪表盘的需求，因此不适用。

内容的提问来源于stack exchange，提问作者DineshS