Using count.index within a value to lookup resources already created

[Paul Schooss]

Hello 

I am trying to use the count.index variable within a resource to use resources already created. I am using  "${concat("aws_subnet.public." , count.index, ".id}")}" as the subnet_id for a resource. However it doesn't really work very well. Since the interpolation of that is a string and not a reference to the resource's real id.

resource "aws_subnet" "public" {

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

cidr_block = "${concat(var.vpc_cidr_block_base, ".", count.index ,".0/24")}"

availability_zone = "${concat(var.region, lookup(var.vpc_availability_zone, concat("zone_", count.index)))}"

count = "${var.zone_count}"

depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}

# Routing table for public subnets

resource "aws_route_table" "public" {

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

route {

cidr_block = "0.0.0.0/0"

gateway_id = "${aws_internet_gateway.default.id}"

}

    depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}

resource "aws_route_table_association" "public" {

subnet_id = "${concat("aws_subnet.public." , count.index, ".id}")}"

route_table_id = "${aws_route_table.public.id}"

count = "${var.zone_count}"

    depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}

[Paul Schooss]

Answered my own question, was using the incorrect way of interpolation.

resource "aws_subnet" "public" {

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

cidr_block = "${concat(var.vpc_cidr_block_base, ".", count.index ,".0/24")}"

availability_zone = "${concat(var.region, lookup(var.vpc_availability_zone, concat("zone_", count.index)))}"

count = "${var.zone_count}"

depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}

# Routing table for public subnets

resource "aws_route_table" "public" {

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

route {

cidr_block = "0.0.0.0/0"

gateway_id = "${aws_internet_gateway.default.id}"

}

    depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}

resource "aws_route_table_association" "public" {

subnet_id = "${aws_subnet.public.${count.index}.id}"

route_table_id = "${aws_route_table.public.id}"

count = "${var.zone_count}"

    depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}

[Paul Schooss]

Ugh still not working....

module.vpc.aws_route_table_association.public.1: Creating...

  route_table_id: "" => "rtb-0668bf63"

  subnet_id:      "" => "${aws_subnet.public.1.id}"

module.vpc.aws_route_table_association.public.0: Creating...

  route_table_id: "" => "rtb-0668bf63"

  subnet_id:      "" => "${aws_subnet.public.0.id}"

module.vpc.aws_route_table_association.public.0: Error: The subnet ID '${aws_subnet.public.0.id}' does not exist (InvalidSubnetID.NotFound)

I think I am going to try this out, https://github.com/hashicorp/terraform/pull/554

[Paul Schooss]

Was able to compile a new version but ran into another issue. 

Error running plan: Resource 'aws_subnet.public' not found for variable 'aws_subnet.public.*.id'

using

resource "aws_subnet" "public" {

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

cidr_block = "${concat(var.vpc_cidr_block_base, ".", count.index ,".0/24")}"

availability_zone = "${concat(var.region, lookup(var.vpc_availability_zone, concat("zone_", count.index)))}"

count = "${var.zone_count}"

depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}

# Routing table for public subnets

resource "aws_route_table" "public" {

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

route {

cidr_block = "0.0.0.0/0"

gateway_id = "${aws_internet_gateway.default.id}"

}

    depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}

resource "aws_route_table_association" "public" {

subnet_id = "${element(aws_subnet.public.*.id,  count.index)}"

route_table_id = "${aws_route_table.public.id}"

count = "${var.zone_count}"

    depends_on = ["aws_vpc.default", "aws_internet_gateway.default"]

}