Create TF Module that implements public/private subnet strategy in existing VPC

[s2504s]

What

• Create TF Module that implements a public & privatesubnet strategy using existing VPC

Why

• Encapsulate business logic of VPCs and Subnets in a module

[osterman]

@s2504s looks great! Just add README.md

[const-bon]

terraform plan has ended with errors.

Error running plan: 1 error(s) occurred:

* module.tf_subnets.aws_route_table_association.public: 2 error(s) occurred:

* module.tf_subnets.aws_route_table_association.public[0]: Resource 'aws_route_table.public' not found for variable 'aws_route_table.public.id'
* module.tf_subnets.aws_route_table_association.public[1]: Resource 'aws_route_table.public' not found for variable 'aws_route_table.public.id'

[const-bon]

There was an issue if we try to use existing AWS Internet Gateway and Default Route Table.

Even if we use code like this it doesn't work.

resource "aws_route_table_association" "public" {
  count = "${length(var.availability_zones)}"
  subnet_id      = "${element(aws_subnet.public.*.id, count.index)}"
  route_table_id = "${signum(length(var.vpc_default_route_table)) == 1 ? var.vpc_default_route_table : aws_route_table.public.id }"
}

Because if we do not create aws_route_table.public (when we use existing route table), Terraform is unable to resolve aws_route_table.public.id and we got an error.

Error running plan: 1 error(s) occurred:

* module.tf_subnets.aws_route_table_association.public: 2 error(s) occurred:

* module.tf_subnets.aws_route_table_association.public[0]: Resource 'aws_route_table.public' not found for variable 'aws_route_table.public.id'
* module.tf_subnets.aws_route_table_association.public[1]: Resource 'aws_route_table.public' not found for variable 'aws_route_table.public.id'

I've pinned igw_id as required value and added resources for two cases: use existing aws_route_table and create new aws_route_table.

resource "aws_route_table_association" "public_new" {
  count = "${signum(length(var.vpc_default_route_table)) == 1 ? 0 : length(var.availability_zones)}"
  subnet_id      = "${element(aws_subnet.public.*.id, count.index)}"
  route_table_id = "${aws_route_table.public.id}"
}

resource "aws_route_table_association" "public_exists" {
  count = "${signum(length(var.vpc_default_route_table)) == 1 ? length(var.availability_zones) : 0}"
  subnet_id      = "${element(aws_subnet.public.*.id, count.index)}"
  route_table_id = "${var.vpc_default_route_table}"
}

[const-bon]

I've tested terraform plan with two cases:

module "tf_subnets" {
  source = "git::https://github.com/cloudposse/tf_subnets.git?ref=init"

  availability_zones      = ["us-east-1a", "us-east-1b"]
  namespace               = "test"
  name                    = "test"
  stage                   = "test"
  region                  = "us-east-1"
  vpc_id                  = "vpc-aceb27ca"
  igw_id                  = "igw-9c26adfb"
  vpc_default_route_table = "rtb-f4f0ce92"
}

module "tf_subnets" {
  source = "git::https://github.com/cloudposse/tf_subnets.git?ref=init"

  availability_zones      = ["us-east-1a", "us-east-1b"]
  namespace               = "test"
  name                    = "test"
  stage                   = "test"
  region                  = "us-east-1"
  vpc_id                  = "vpc-aceb27ca"
  igw_id                  = "igw-9c26adfb"
}

Both are ok.

[const-bon]

@osterman please review

[osterman]

We should suffix with _id if it refers to an ID (for consistency).

[const-bon]

Added.

[osterman]

I think we should call this public_default

[const-bon]

Renamed.

[osterman]

Let's call this public so it's symetrical with aws_route_table.public

[const-bon]

Renamed.

[const-bon]

Added required fixes.
@osterman please approve.