Support multiple EBS volumes attached and persisted to single node ASG.

[Magicloud]

This change contains multiple changes to modules, to support having multiple persisted EBS attached to single node ASG.

The problem is that, since this is a breaking change, many variables/outputs are different. I think we should make them new modules to avoid breaking current code.

[Magicloud]

@ketzacoatl The change works, but not the final code (filling up description and so) since I'd like to hear your idea. Is it better to make another few modules instead of making breaking changes to original modules?

[ketzacoatl]

@Magicloud do we also want to create a copy of the previous single-node-asg module to allow users access to the previous workflow?

[qrilka]

@Magicloud what's the status of this? Do you plan to add README as requested above and add a module to use with the previous workflow?

[Magicloud]

Please add a README and Makefile with the example, and include in the README notes on how to use the example and run the tests.

Done.

[qrilka]

I tried to create an ASG with no extra volumes (passing []) got an error during apply:

Error: Invalid index

  on .terraform/modules/asg-a/modules/init-snippet-attach-ebs-volume/main.tf line 19, in data "template_file" "init_snippet":
  19:     device_path   = var.device_paths[count.index]
    |----------------
    | count.index is 0
    | var.device_paths is empty list of string

The given key does not identify an element in this collection value.

[Magicloud]

I tried to create an ASG with no extra volumes (passing []) got an error during apply:

Error: Invalid index

  on .terraform/modules/asg-a/modules/init-snippet-attach-ebs-volume/main.tf line 19, in data "template_file" "init_snippet":
  19:     device_path   = var.device_paths[count.index]
    |----------------
    | count.index is 0
    | var.device_paths is empty list of string

The given key does not identify an element in this collection value.

@qrilka Does this happen on existing resources? I tried from beginning, no problem.

[qrilka]

@Magicloud yes, probably that was the reason - I switched from master version to this branch

[qrilka]

So probably it could be a problem when upgrading modules (and when this will get merged)

[Magicloud]

@qrilka I see. Since the logic is changed totally, it could break.

[qrilka]

@Magicloud while using this branch for A/B switching demo I have found that tags cause unnecessary updates like the following:

  # module.asg-magenta.module.service-data.aws_ebs_volume.main[0] will be updated in-place
  ~ resource "aws_ebs_volume" "main" {
        arn                  = "arn:aws:ec2:us-west-2:xxxxx:volume/vol-xxxxx"
        availability_zone    = "us-west-2a"
        encrypted            = true
        id                   = "vol-xxxx"
        iops                 = 100
        kms_key_id           = "arn:aws:kms:us-west-2:xxxx:key/xxxx-ae63-4278-bba4-xxxx"
        multi_attach_enabled = false
        size                 = 20
      ~ tags                 = {
            "Name"             = "switching-demo-magenta-us-west-2a-a"
          - "cldy-instance-id" = "i-0b4f3320df090f7ca" -> null
        }
        type                 = "gp2"
    }

[Magicloud]

@qrilka Where does that tag come from?

[qrilka]

That's a good question but I have not idea and not sure if I will have time to find it out...

[ketzacoatl]

That tag is unrelated and we should not have blocked this PR on that. Unless there's reason to hold back, I think we should merge this PR.