refresh doesn't update the fields of stopped AWS instances

[fatih]

Hi,

I've search the issue tracker but couldn't find any related issue. Please feel free to close if this is a duplicate. Having a simple aws_instance resource (full version: https://gist.github.com/fatih/e93aa6f6e9a763ec5957) in the form of:

resource "aws_instance" "web" {
  instance_type = "t2.micro"
  ami = "ami-9e5cff9e"
}

Because it doesn't have an eip, the Public IP will change in every stop/start switch. So the weird thing is, when the instance is stopped, and I call terraform refresh, it still shows the old public IP:

aws_instance.web:
  ...
  public_ip = 54.65.84.208
  ...

If I start the instance manually and call terraform refresh again, it goes and picks up the IP (which changed because it wasn't using eip, as expected):

aws_instance.web:
  ...
  public_ip = 53.35.164.216
  ...

So my question is, why is the state not set to an empty value, if the instance is stopped and I call terraform refresh? I think this is a bug, but I'm not sure. So basically all I want is that terraform show to display the following when the instance is stopped and doesn't have any public IP anymore:

aws_instance.web:
  ...
  public_ip = 
  ...

Is this a wrong assumption?

[phinze]

Hi @fatih - This sounds like reasonable logic to me, but I'd imagine it would be difficult to implement if it diverges from the behavior of the AWS API. Does aws ec2 describe-instances yield an empty or a last-known public IP for stopped instances? If it's empty, then yeah definitely a bug. If it's populated, then I'm not sure if we want to special-case away from the API behavior.

[phinze]

Tagging as bug tentatively and we can see what we find out. 😀

[fatih]

I've tested it with the aws-cli and it doesn't return it, aka it's empty. Which makes sense because a stopped instance really doesn't have any IP at all. And terraform show shows the old IP, which theoretically is invalid because it's being released to the IP pool when you switch it. So there is the probability it's being used by someone else.

So I've dived into the code and found that the API call returns a null response, instead of an empty string. For Example the public_dns field returns an empty string, but for public_ip it returns a null. So because of that it doesn't update the state correctly.

I've tried to debugged it and found that we need to set it explicitly to an empty value. This is already the case for maps(https://github.com/hashicorp/terraform/blob/master/helper/schema/field_writer_map.go#L139) , but not for the primivite values. Here is the fix: #3257

[ghost]

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