Terraform中的for_each和count
通过Terraform创建云主机时，在某些业务场景下，一个机器需要挂载多个云盘，一般云厂商都是单独创建云主机和云硬盘然后通过attachment的资源去挂载，因此我们的模板大致如下：resource "tencentcloud_instance" "basic" {
instance_name = var.instance_name
password = "xxx"
}
resource "tencentcloud_cbs_storage" "storage" {
for_each = var.data_disks
storage_name = each.key
storage_type = each.value.disk_type
storage_size = each.value.size
}
resource "tencentcloud_cbs_storage_attachment" "attachment" {
count = length(tencentcloud_cbs_storage.storage)
storage_id= element(values(tencentcloud_cbs_storage.storage)[*].id, count.index)
instance_id = tencentcloud_instance.basic.id
}
variable "data_disks" {
type = map(object({
disk_type = string
size = number
}))
description = "Instance Data Disks"
default = {}
}这个模板我们不停用了很久，完全满足多盘的需求，也具有一定机动性，但是随着全方位降本的需求，在服务优化等措施下，业务方评估可以考虑减少云盘数量，因为机型的特殊性，机器也不能回收重新创建。
因为之前不停没有减盘的场景，所以不停没关注，直到最近业务方评估需要减盘，发现在减盘时盘的attachment会销毁重新创建，腾讯云这个资源的操作会伴随unmount动作，导致减盘之后盘没有被挂载上
这个征象是不在我的预期当中的，分析Terraform的日记：
# tencentcloud_cbs_storage_attachment.attachment must be replaced
-/+ resource "tencentcloud_cbs_storage_attachment" "attachment" {
~ id = "disk-mcklmp5z" -> (known after apply)
~ storage_id= "disk-mcklmp5z" -> "disk-rspjpenh" # forces replacement
# (1 unchanged attribute hidden)
}
# tencentcloud_cbs_storage_attachment.attachment must be replaced
-/+ resource "tencentcloud_cbs_storage_attachment" "attachment" {
~ id = "disk-rspjpenh" -> (known after apply)
~ storage_id= "disk-rspjpenh" -> "disk-k9c5lg1v" # forces replacement
# (1 unchanged attribute hidden)
}
# tencentcloud_cbs_storage_attachment.attachment must be replaced
-/+ resource "tencentcloud_cbs_storage_attachment" "attachment" {
~ id = "disk-k9c5lg1v" -> (known after apply)
~ storage_id= "disk-k9c5lg1v" -> "disk-jl5g1u7f" # forces replacement
# (1 unchanged attribute hidden)
}
# tencentcloud_cbs_storage_attachment.attachment must be replaced
-/+ resource "tencentcloud_cbs_storage_attachment" "attachment" {
~ id = "disk-jl5g1u7f" -> (known after apply)
~ storage_id= "disk-jl5g1u7f" -> "disk-mytvnnif" # forces replacement
# (1 unchanged attribute hidden)
}发现attachment的索引是index，减盘的时候索引会重新计算，这就是attachment资源被销毁重建，导致云盘被卸载的原因。
原因明确了，那就好解决了，可以用for_each来解决这个问题，如下：
resource "tencentcloud_cbs_storage_attachment" "attachment" {
for_each = toset(values(tencentcloud_cbs_storage.storage)[*].id)
storage_id= each.key
instance_id = tencentcloud_instance.foo.id
}事情每每没那么顺遂：
│ Error: Invalid for_each argument
│
│ on main.tf line 61, in resource "tencentcloud_cbs_storage_attachment" "attachment":
│ 61: for_each = toset(values(tencentcloud_cbs_storage.storage)[*].id)
│ ├────────────────
│ │ tencentcloud_cbs_storage.storage is object with 6 attributes
│
│ The "for_each" value depends on resource attributes that cannot be
│ determined until apply, so Terraform cannot predict how many instances will
│ be created. To work around this, use the -target argument to first apply
│ only the resources that the for_each depends on.好吧，在Terraform论坛发现一个issue：
https://discuss.hashicorp.com/t/the-for-each-value-depends-on-resource-attributes-that-cannot-be-determined-until-apply/25016
https://img2024.cnblogs.com/other/3300446/202408/3300446-20240822200928693-786655883.png
简而言之，就是foreach要求他的map key必须是已知明确的值，不能是依赖其他资源的值，所以会有如上错误。知道限制了调整下模板：
resource "tencentcloud_cbs_storage_attachment" "attachment" {
for_each = var.data_disks
storage_id= tencentcloud_cbs_storage.storage.id
instance_id = tencentcloud_instance.basic.id
}圆满解决，新创建的实例用上新的模板，但是存量的实例无法调整还是得忍受下盘重新挂载的问题。
免责声明：如果侵犯了您的权益，请联系站长，我们会及时删除侵权内容，谢谢合作！更多信息从访问主页：qidao123.com:ToB企服之家，中国第一个企服评测及商务社交产业平台。
页:
[1]