如何将S3桶通知列表合并为桶名作为键的映射（Terraform）

需要将多组S3桶通知的列表转换为以桶名为唯一键、对应值为该桶所有通知条目数组的映射结构，以此通过dynamic块遍历生成S3桶通知资源。

现有通知列表 #

buckets_with_events = [
  {
    "bucket" = "bucket1"
    "events" = [
      "s3:ObjectCreated:*",
    ]
    "filter_prefix" = tostring(null)
    "filter_suffix" = ".xml"
    "function" = "lambda1"
  },
  {
    "bucket" = "bucket1"
    "events" = [
      "s3:ObjectCreated:*",
    ]
    "filter_prefix" = tostring(null)
    "filter_suffix" = ".csv"
    "function" = "lambda1"
  },
  {
    "bucket" = "bucket2"
    "events" = [
      "s3:ObjectCreated:*",
    ]
    "filter_prefix" = tostring(null)
    "filter_suffix" = ".csv"
    "function" = "lambda1"
  }
]

尝试的错误代码 #

之前的写法无法正确将条目分组到对应桶名的键下：

bucket_events = flatten([
  for parent_obj in local.buckets_with_events:
      parent_obj.bucket => [
        for obj in local.buckets_with_events:
          {events = obj.events
           filter_suffix = obj.filter_suffix} if parent_obj.bucket == obj.bucket
  ]
])

期望输出格式 #

bucket_events = {
  "bucket1" = [
    {
      "events" = [
        "s3:ObjectCreated:*",
      ]
      "filter_prefix" = tostring(null)
      "filter_suffix" = ".xml"
      "function" = "lambda1"
    },
    {
      "events" = [
        "s3:ObjectCreated:*",
      ]
      "filter_prefix" = tostring(null)
      "filter_suffix" = ".csv"
      "function" = "lambda1"
    }
  ]
  "bucket2" = [
    {
      "events" = [
        "s3:ObjectCreated:*",
      ]
      "filter_prefix" = tostring(null)
      "filter_suffix" = ".csv"
      "function" = "lambda1"
    }
  ]
}

正确实现代码 #

通过先提取唯一桶名，再为每个桶名收集对应通知条目的方式，生成目标映射：

bucket_events = {
  for bucket_name in distinct(local.buckets_with_events[*].bucket) :
  bucket_name => [
    for item in local.buckets_with_events :
    item if item.bucket == bucket_name
  ]
}

代码说明 #

1. distinct(local.buckets_with_events[*].bucket)：提取列表中所有唯一的桶名，避免重复处理
2. 外层for表达式：以每个唯一桶名为键，生成对应的条目数组
3. 内层for表达式：遍历原始列表，筛选出当前桶名下的所有通知条目

资源生成示例（修正后） #

使用生成的映射遍历创建S3桶通知资源，修正dynamic块中的变量引用错误：

resource "aws_s3_bucket_notification" "dynamic_s3_triggers" {
  for_each = local.bucket_events
  bucket   = each.key

  dynamic "lambda_function" {
    for_each = lambda_function.value
    content {
      lambda_function_arn = aws_lambda_function.functions[lambda_function.value.function].arn
      events              = lambda_function.value.events
      filter_prefix       = lambda_function.value.filter_prefix
      filter_suffix       = lambda_function.value.filter_suffix
    }
  }
}

内容的提问来源于stack exchange，提问作者Robin Tanner