Unchanged aws_vpc resource recreated due to assign_generated_ipv6_cidr_block

[dominics]

I've noticed a regression on master (which I'm running to get the fix for an unrelated issue)

Terraform Version

v0.9.2-dev - rough bisect, strongly suspect any commit after bed23ff

Affected Resource(s)

• aws_vpc

Terraform Configuration Files

resource "aws_vpc" "vpc" {
  cidr_block           = "172.20.0.0/16"
  enable_dns_support   = true
  enable_dns_hostnames = true

  tags {
    Name = "default"
  }

  lifecycle {
    create_before_destroy = true
  }
}

Expected Behavior

No changes on terraform plan after 0.9.2-dev/master upgrade

Actual Behavior

Plan attempts to force-recreate the VPC, showing a "" => "false" difference on assign_generated_ipv6_cidr_block:

-/+ module.vpc.aws_vpc.vpc
    assign_generated_ipv6_cidr_block: "" => "false" (forces new resource)
    cidr_block:                       "172.20.0.0/16" => "172.20.0.0/16"
    default_network_acl_id:           "acl-abcdef01" => "<computed>"
    default_route_table_id:           "rtb-abcdef01" => "<computed>"
    default_security_group_id:        "sg-abcdef01" => "<computed>"
    dhcp_options_id:                  "dopt-abcdef01" => "<computed>"
    enable_classiclink:               "false" => "<computed>"
    enable_dns_hostnames:             "true" => "true"
    enable_dns_support:               "true" => "true"
    instance_tenancy:                 "default" => "<computed>"
    ipv6_association_id:              "" => "<computed>"
    ipv6_cidr_block:                  "" => "<computed>"
    main_route_table_id:              "rtb-abcdef01" => "<computed>"
    tags.%:                           "1" => "1"
    tags.Name:                        "default" => "default"

I added assign_generated_ipv6_cidr_block = false explicitly, to attempt to work around the problem, and it worked at least some of the time. But I still (in some environments?!) saw plans that attempted to recreate the VPC.

Steps to Reproduce

• Create this resource using a stable version, like 0.9.1
• Upgrade to latest master version
• terraform plan

References

• provider/aws: Set aws_vpc ipv6 for associated only #12899

[stack72]

Hi @dominics

You are indeed correct - I am sorry for this issue - I am opening a PR right now that will migrate the state for you and take care of it

Paul

[brianwallace]

Pretty sure I am still seeing this behavior in terraform v0.9.2:

The following snippet is from a terraform plan on pre-0.9.2 configuration:

-/+ module.template.aws_vpc.main
    assign_generated_ipv6_cidr_block: "" => "false" (forces new resource)
    cidr_block:                       "10.0.0.0/16" => "10.0.0.0/16"
    default_network_acl_id:           "acl-8f9602ea" => "<computed>"
    default_route_table_id:           "rtb-5b16843e" => "<computed>"
    default_security_group_id:        "sg-0e45a36a" => "<computed>"
    dhcp_options_id:                  "dopt-15776477" => "<computed>"
    enable_classiclink:               "false" => "<computed>"
    enable_dns_hostnames:             "true" => "true"
    enable_dns_support:               "true" => "true"
    instance_tenancy:                 "default" => "<computed>"
    ipv6_association_id:              "" => "<computed>"
    ipv6_cidr_block:                  "" => "<computed>"
    main_route_table_id:              "rtb-5b16843e" => "<computed>"
    tags.%:                           "3" => "3"
    tags.Environment:                 "staging" => "staging"
    tags.KubernetesCluster:           "midgard" => "midgard"
    tags.Name:                        "staging" => "staging"

I attempted to add assign_generated_ipv6_cidr_block = false to the vpc resource, but it did not seem to make a difference.

UPDATE 4/5/2017: I think this is the same issue identified and fixed in Issue #13197. Looks like it will be in v0.9.3.

[ghost]

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