How to assign unique names to EC2 instances

[mak...@hotpads.com]

Hello everyone!

I'm building an infrastructure where we need to use unique "Name" tag for each EC2 instance, as we have other script dependending on that.

My original idea was based on this page and it looked like:

resource "aws_instance" "server" {

  tags = {

    "Name" = SERVERNAME-"${self.private_ip_address}"


  }

}

However, after digging through Terraform documentation and PRs I found that it is not possible to use ${self.ATTRIBUTE} (like seld.id or seld.private_ip_address) while provisioning instance. 

PR 1033 states that it cannot be used within the "resource" itself.

On other hand it is not possible to use random number as well, because those nodes would be reprovisioned every time we run Terraform.

Would someone please recommend on how to generate  and use unique instance name.

Thank you,

Maxim

[David Adams]

I believe this sort of thing is what https://www.terraform.io/docs/providers/random/r/id.html is designed for.

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[Paddy Foran]

Hi Maxim,

I could be wrong about this, as I'm relatively new to Terraform, but if you're looking for a unique value in the tag, I think you should be able to use the built-in random provider to generate a random ID that will only change when the resource is created. https://www.terraform.io/docs/providers/random/

Hope that helps!

Thanks,

Paddy

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[Maxim Fedchyshyn]

Thank you David and Paddy for your answers!

I was trying to use random ID with the same code as shown on example page but it was in fact generating two instances with the same random part in the name. That was weird. :)

After asking this question I played with different options and now I'm using  ${count.index}  and thinking about migrating to autoscaling group and using name_prefix option.

Thanks,

Maxim

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[ben.mi...@scrippsnetworks.com]

I'm running into the same issue. I'm writing a stack template for Azure where developers will spin up a couple of VMs (and associated resources) using this same TF Template (from Jenkins) and I need a way to make the resource names unique (since they will deploy to the same Resource Group and Storage Container).  I though I could do this with the "random_id" resource - but i'm struggling to understand it's syntax. When I spin up the two VMs it is giving them the same name (though they include random characters).   

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[Maxim Fedchyshyn]

Ben,

I was thinking about similar use case. In my opinion it might worth to pass required name as Jenkins input parameter. You could configure Jenkins to define an input before running provisioning task, and configure TF scripts to use that parameter.

Hope that helps!     

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[Martin Atkins]

Hi Maxim,

It sounded like you found a different solution here, but to clarify on the random_id resource: you would need to have a separate random_id instance for each random id you want to generate. The random_id resource exists to create and retain a random id, so it is by design that once a given resource has been created it will return the same id until it is recreated.

To get multiple ids you can either have multiple separate random_id configuration blocks in your config or you can use the count attribute on a single block to generate multiple ids with the same settings.

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