Gist for https://github.com/hashicorp/terraform/issues/3429

main.tf

provider "aws" {
  region = "us-west-2"
}

variable "server_count" {
  default = 4
}

resource "aws_eip" "ip" {
  count    = "${var.server_count}"
  instance = "${element(aws_instance.example.*.id, count.index)}"
  vpc      = true
}

resource "aws_instance" "example" {
  count                       = "${var.server_count}"
  ami                         = "ami-dfc39aef"
  instance_type               = "t2.nano"
  associate_public_ip_address = true
  subnet_id                   = "${aws_subnet.us-west-2b-public.id}"
  availability_zone           = "${aws_subnet.us-west-2b-public.availability_zone}"

  tags {
    Name = "tf-issue-3429-repro"
  }

  lifecycle {
    create_before_destroy = true
  }
}

resource "aws_route53_record" "ec2_instance_fqdn" {
  count   = "${var.server_count}"
  zone_id = "${var.hosted_zone_id}"
  name    = "${format("%v-%02d.%v", var.role, count.index+1, var.domain)}"
  type    = "CNAME"
  ttl     = "60"
  records = ["${element(aws_instance.example.*.private_dns, count.index)}"]
}

variable "role" {
  default = "example"
}

variable "domain" {
  default = "exmaple.com"
}

variable "hosted_zone_id" {
  default = "XXXXXXXXXXXXX"
}

resource "aws_vpc" "example" {
	cidr_block = "10.0.0.0/16"
}

resource "aws_internet_gateway" "example" {
	vpc_id = "${aws_vpc.example.id}"
}

resource "aws_subnet" "us-west-2b-public" {
	vpc_id = "${aws_vpc.example.id}"

	cidr_block = "10.0.0.0/24"
	availability_zone = "us-west-2b"
}

resource "aws_route_table" "us-west-2-public" {
	vpc_id = "${aws_vpc.example.id}"

	route {
		cidr_block = "0.0.0.0/0"
		gateway_id = "${aws_internet_gateway.example.id}"
	}
}

resource "aws_route_table_association" "us-west-2b-public" {
	subnet_id = "${aws_subnet.us-west-2b-public.id}"
	route_table_id = "${aws_route_table.us-west-2-public.id}"
}

output.log

> awsu exec terraform taint aws_instance.example.0
The resource aws_instance.example.0 in the module root has been marked as tainted!

> awsu exec terraform apply
aws_vpc.example: Refreshing state... (ID: vpc-4ed29a29)
aws_internet_gateway.example: Refreshing state... (ID: igw-fbcadf9f)
aws_subnet.us-west-2b-public: Refreshing state... (ID: subnet-8dc0a6ea)
aws_route_table.us-west-2-public: Refreshing state... (ID: rtb-46b14220)
aws_instance.example.0: Refreshing state... (ID: i-0f26591f4be67e722)
aws_instance.example.2: Refreshing state... (ID: i-00cf35593dd0980e6)
aws_instance.example.1: Refreshing state... (ID: i-053728ba715cc1e69)
aws_instance.example.3: Refreshing state... (ID: i-0e98782b96477aca5)
aws_route_table_association.us-west-2b-public: Refreshing state... (ID: rtbassoc-6f9c8709)
aws_eip.ip.1: Refreshing state... (ID: eipalloc-e6e21080)
aws_route53_record.ec2_instance_fqdn.3: Refreshing state... (ID: XXXXXXXXXXXXX_example-04.example.com_CNAME)
aws_eip.ip.3: Refreshing state... (ID: eipalloc-6be0120d)
aws_eip.ip.0: Refreshing state... (ID: eipalloc-3dff0d5b)
aws_eip.ip.2: Refreshing state... (ID: eipalloc-57e61431)
aws_route53_record.ec2_instance_fqdn.2: Refreshing state... (ID: XXXXXXXXXXXXX_example-03.example.com_CNAME)
aws_route53_record.ec2_instance_fqdn.1: Refreshing state... (ID: XXXXXXXXXXXXX_example-02.example.com_CNAME)
aws_route53_record.ec2_instance_fqdn.0: Refreshing state... (ID: XXXXXXXXXXXXX_example-01.example.com_CNAME)
aws_instance.example.0: Creating...
  ami:                         "" => "ami-dfc39aef"
  associate_public_ip_address: "" => "true"
  availability_zone:           "" => "us-west-2b"
  ebs_block_device.#:          "" => "<computed>"
  ephemeral_block_device.#:    "" => "<computed>"
  instance_state:              "" => "<computed>"
  instance_type:               "" => "t2.nano"
  key_name:                    "" => "<computed>"
  network_interface_id:        "" => "<computed>"
  placement_group:             "" => "<computed>"
  private_dns:                 "" => "<computed>"
  private_ip:                  "" => "<computed>"
  public_dns:                  "" => "<computed>"
  public_ip:                   "" => "<computed>"
  root_block_device.#:         "" => "<computed>"
  security_groups.#:           "" => "<computed>"
  source_dest_check:           "" => "true"
  subnet_id:                   "" => "subnet-8dc0a6ea"
  tags.%:                      "" => "1"
  tags.Name:                   "" => "tf-issue-3429-repro"
  tenancy:                     "" => "<computed>"
  vpc_security_group_ids.#:    "" => "<computed>"
aws_instance.example.0: Still creating... (10s elapsed)
aws_instance.example.0: Creation complete
aws_eip.ip.0: Modifying...
  instance: "i-0f26591f4be67e722" => "i-020a1925c3e7e60d9"
aws_route53_record.ec2_instance_fqdn.0: Modifying...
  records.2781236304: "" => "ip-10-0-0-90.us-west-2.compute.internal"
  records.320270958:  "ip-10-0-0-205.us-west-2.compute.internal" => ""
aws_route53_record.ec2_instance_fqdn.0: Still modifying... (10s elapsed)
aws_route53_record.ec2_instance_fqdn.0: Still modifying... (20s elapsed)
aws_route53_record.ec2_instance_fqdn.0: Still modifying... (30s elapsed)
aws_route53_record.ec2_instance_fqdn.0: Still modifying... (40s elapsed)
aws_route53_record.ec2_instance_fqdn.0: Modifications complete
Error applying plan:

1 error(s) occurred:

* aws_eip.ip.0: Failure associating EIP: Resource.AlreadyAssociated: resource eipalloc-3dff0d5b is already associated with associate-id eipassoc-dfb259a2
	status code: 400, request id: a2762deb-18a5-4dea-ace5-94045976dc64

Terraform does not automatically rollback in the face of errors.
Instead, your Terraform state file has been partially updated with
any resources that successfully completed. Please address the error
above and apply again to incrementally change your infrastructure.