Terraform 循环依赖 [英] Terraform cyclic dependency

问题描述

我正在尝试通过 Terraform 实例化 3 个知道彼此 IP 地址的 aws_instance.这当然会导致循环依赖.我想知道克服这个问题的最佳方法是什么.我尝试了几种解决方案:

I'm trying to instantiate 3 aws_instances that are aware of each other ip address via Terraform. This of course results in a cyclic dependency. I was wondering what is the best way to overcome this problem. I've tried a couple of solutions:

1. 一起实例化 2 个实例，然后实例化 1 个依赖于这 2 个实例的实例.在第三个实例中，有一个 user_data 脚本，允许实例通过 ssh 连接到其他 2 个实例以设置必要的配置.

它有效，但我不喜欢它创建 2 个不同的资源组的事实，即使这 3 个实例在初始化后的所有意图和目的都是相同的.

It works, but I don't like the fact that it creates 2 distinct groups of resources even though the 3 instances are for all intent and purpose identical after init.

1. 同时实例化 3 个实例，然后实例化另一个实例，其唯一目的是 ssh 进入每个实例以设置必要的配置.初始化完成后，附加实例应自行终止.

它也可以，但是 terraform 会将第 4 个资源视为已终止的资源，并会在有更新时尝试重新创建它，因此这不是很干净.

It also works, but then terraform will see the 4th resource as a terminated resource and will try to recreate it whenever there is an update so this is not very clean.

有什么建议吗?谢谢.

这是一个不能与 remote-exec 一起工作的尝试来说明循环依赖:

Here is an attempt that doesn't work with remote-exec to illustrate the cyclic dependency:

resource "aws_instance" "etcd" {
  count           = 3

  ami             = data.aws_ami.ubuntu.id
  instance_type   = "t3.micro"
  subnet_id       = module.vpc.public_subnets[count.index].id

  provisioner "remote-exec" {
    inline = [
      "echo ${aws_instance.etcd[0].private_ip}",
      "echo ${aws_instance.etcd[1].private_ip}",
      "echo ${aws_instance.etcd[2].private_ip}"
    ]
  }
}

推荐答案

根据评论.

您可以使用 remote-exec 在您的三个实例，仅在全部配置完成后.你必须开发这样一个脚本来 ssh 到他们三个.

You could use remote-exec to run code on your three instance, only after all of them have been provisioned. You would have to develop such a script to ssh to the three of them.

但是，您只能在第三个实例启动后调用您的 remote-exec 脚本.这可以通过使用 null_resoruce 来实现，这取决于实例.

But, you would only invoke your remote-exec script after the third instance is up. This can be achieved by using null_resoruce which would depend on the instances.

无资源的供应商中描述了这种使用 null_resource 的方式.

This way of using null_resource is described in Provisioners Without a Resource.

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