VPC IP不正确

我试图得到VPC实例IP的输出和IP不正确这里是我的配置

resource "aws_vpc" "default" {
    cidr_block = "${var.vpc_cidr}"
    enable_dns_hostnames = true
    tags {
        Name = "terraform-aws-vpc"
    }
}

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

/*
  NAT Instance
*/
resource "aws_security_group" "nat" {
    name = "vpc_nat"
    description = "Allow traffic to pass from the private subnet to the internet"

    ingress {
        from_port = 80
        to_port = 80
        protocol = "tcp"
        cidr_blocks = ["${var.private_subnet_cidr}"]
    }
    ingress {
        from_port = 443
        to_port = 443
        protocol = "tcp"
        cidr_blocks = ["${var.private_subnet_cidr}"]
    }
    ingress {
        from_port = 22
        to_port = 22
        protocol = "tcp"
        cidr_blocks = ["0.0.0.0/0"]
    }
    ingress {
        from_port = -1
        to_port = -1
        protocol = "icmp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    egress {
        from_port = 80
        to_port = 80
        protocol = "tcp"
        cidr_blocks = ["0.0.0.0/0"]
    }
    egress {
        from_port = 443
        to_port = 443
        protocol = "tcp"
        cidr_blocks = ["0.0.0.0/0"]
    }
    egress {
        from_port = 22
        to_port = 22
        protocol = "tcp"
        cidr_blocks = ["${var.vpc_cidr}"]
    }
    egress {
        from_port = -1
        to_port = -1
        protocol = "icmp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    vpc_id = "${aws_vpc.default.id}"

    tags {
        Name = "NAT"
    }
}

resource "aws_instance" "nat" {
    ami = "ami-30913f47" # this is a special ami preconfigured to do NAT
    availability_zone = "eu-west-1a"
    instance_type = "m1.small"
    key_name = "admin_key"
    vpc_security_group_ids = ["${aws_security_group.nat.id}"]
    subnet_id = "${aws_subnet.eu-west-1a-public.id}"
    associate_public_ip_address = true
    source_dest_check = false

    tags {
        Name = "VPC NAT"
    }
}

resource "aws_eip" "nat" {
    instance = "${aws_instance.nat.id}"
    vpc = true
}

/*
  Public Subnet
*/
resource "aws_subnet" "eu-west-1a-public" {
    vpc_id = "${aws_vpc.default.id}"

    cidr_block = "${var.public_subnet_cidr}"
    availability_zone = "eu-west-1a"

    tags {
        Name = "Public Subnet"
    }
}

resource "aws_route_table" "eu-west-1a-public" {
    vpc_id = "${aws_vpc.default.id}"

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

    tags {
        Name = "Public Subnet"
    }
}

resource "aws_route_table_association" "eu-west-1a-public" {
    subnet_id = "${aws_subnet.eu-west-1a-public.id}"
    route_table_id = "${aws_route_table.eu-west-1a-public.id}"
}

/*
  Private Subnet
*/
resource "aws_subnet" "eu-west-1a-private" {
    vpc_id = "${aws_vpc.default.id}"

    cidr_block = "${var.private_subnet_cidr}"
    availability_zone = "eu-west-1a"

    tags {
        Name = "Private Subnet"
    }
}

resource "aws_route_table" "eu-west-1a-private" {
    vpc_id = "${aws_vpc.default.id}"

    route {
        cidr_block = "0.0.0.0/0"
        instance_id = "${aws_instance.nat.id}"
    }

    tags {
        Name = "Private Subnet"
    }
}

resource "aws_route_table_association" "eu-west-1a-private" {
    subnet_id = "${aws_subnet.eu-west-1a-private.id}"
    route_table_id = "${aws_route_table.eu-west-1a-private.id}"
}


output "NAT_Private_IP" {
  value = "${aws_instance.nat.private_ip}"
}

我测试了以下内容

aws_instance.nat.public_ip

和

aws_eip.nat.public_ip

但是当使用aws_instance.nat.public_ip时没有机会这样做它给出了不正确的ip，这个代码基于terraform AWS而我正在尝试制作VPC堡垒主机