Terraform EC2 实例导入 - 用户数据不同

Question

I am attempting to import an existing EC2 instance into Terraform. I have taken the EC2 instance User Data, and added it to my TF config file eg

    user_data               = <<EOF
<powershell>
& $env:SystemRoot\System32\control.exe "intl.cpl,,/f:`"UKRegion.xml`""
& tzutil /s "GMT Standard Time" 
Set-Culture en-GB
</powershell>
EOF

The resource imports OK, but when I run terraform plan I get TF wanting to destroy and recreate the instance, as a 'change' in user_data 'forces new resource'.

user_data: "946f756af0df239b19f86a72653e58dcc04c4b27" => "811599030dc713b18c3e35437a82b35095190a81" (forces new resource)

I have tried copy and pasting the user data from EC2 console into the TF file, but this is not working. Is this at all possible?

Answer 1

Per this github issue , it looks like this is an issue with how terraform interprets the user_data as a "computed" value. There appears to be a work around.

• First run a plan/apply cycle with your plan command including the extra argument on your command line:
  -target=template_file.userdata-consul. This will tell Terraform to do the minimal work it needs to update the template file, which should
  leave your launch configuration untouched.
• Now run plan again, and since the template_file has now already been recreated it should interpolate the resolved template as expected into the user_data, and there should then be no diff because the "new" template rendering should be the same as the "old" one.

Answer 2

You can't copy the user_data value from the state, as it is an encoded string and if you copy it into the resource configuration, it'll get encoded again before it is compared to the current state, and it won't match.

But you can copy the current user data value from the Instance settings in the EC2 Console, and paste it into the user_data attribute of the resoure in the .tf file.

If there are multiple lines of data, you will need to replace each new-line with a \\n in the file, as you can't use a multi-line string.

For example:

resource "aws_instance" "instance1" {
  ami = "ami-0123456789abcdef0"
  instance_type = "t4.medium"
  user_data = "setting1=value\nsetting2=value\nsetting3=value"
}

Note: there is a 16KB size limit on the user data in EC2, but if you're copying from EC2 to your Terraform configuration, this won't be an issue. (But it will make it difficult to read and manage, so you may want to consider storing the config in a custom image instead.)

Or, as you suggested already, if your setup supports this and you can afford to shut the instance down temporarily, remove the user data from the instance settings altogether.