provider/aws: Adding IPv6 address to instance causes perpetual diff

[stack72]

Fixes: #14032

When you are using an IPv6 address directly to an instance, it was
causing the ipv6_address_count to try and ForceNew resource. It wasn't
marked as computed

I was able to reproduce this:

-/+ aws_instance.test
    ami:                          "ami-c5eabbf5" => "ami-c5eabbf5"
    associate_public_ip_address:  "false" => "<computed>"
    availability_zone:            "us-west-2a" => "<computed>"
    ebs_block_device.#:           "0" => "<computed>"
    ephemeral_block_device.#:     "0" => "<computed>"
    instance_state:               "running" => "<computed>"
    instance_type:                "t2.micro" => "t2.micro"
    ipv6_address_count:           "1" => "0" (forces new resource)
    ipv6_addresses.#:             "1" => "1"
    ipv6_addresses.0:             "2600:1f14:bb2:e501::10" => "2600:1f14:bb2:e501::10"
    key_name:                     "" => "<computed>"
    network_interface.#:          "0" => "<computed>"
    network_interface_id:         "eni-d19115ec" => "<computed>"
    placement_group:              "" => "<computed>"
    primary_network_interface_id: "eni-d19115ec" => "<computed>"
    private_dns:                  "ip-10-20-1-252.us-west-2.compute.internal" => "<computed>"
    private_ip:                   "10.20.1.252" => "<computed>"
    public_dns:                   "" => "<computed>"
    public_ip:                    "" => "<computed>"
    root_block_device.#:          "1" => "<computed>"
    security_groups.#:            "0" => "<computed>"
    source_dest_check:            "true" => "true"
    subnet_id:                    "subnet-3fdfb476" => "subnet-3fdfb476"
    tags.%:                       "1" => "1"
    tags.Name:                    "stack72" => "stack72"
    tenancy:                      "default" => "<computed>"
    volume_tags.%:                "0" => "<computed>"
    vpc_security_group_ids.#:     "1" => "<computed>"

It now works as expected:

% terraform plan                                                                                 ✹ ✭
[WARN] /Users/stacko/Code/go/bin/terraform-provider-aws overrides an internal plugin for aws-provider.
  If you did not expect to see this message you will need to remove the old plugin.
  See https://www.terraform.io/docs/internals/internal-plugins.html
Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but will not be
persisted to local or remote state storage.

aws_vpc.foo: Refreshing state... (ID: vpc-fa61669d)
aws_subnet.foo: Refreshing state... (ID: subnet-3fdfb476)
aws_internet_gateway.foo: Refreshing state... (ID: igw-70629a17)
aws_route_table.test: Refreshing state... (ID: rtb-0a52e16c)
aws_instance.test: Refreshing state... (ID: i-0971755345296aca5)
aws_route_table_association.a: Refreshing state... (ID: rtbassoc-b12493c8)
No changes. Infrastructure is up-to-date.

This means that Terraform did not detect any differences between your
configuration and real physical resources that exist. As a result, Terraform
doesn't need to do anything.

[grubernaut]

LGTM

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.