provider/aws: aws_main_route_table_association

[phinze]

This resource allows an existing Route Table to be assigned as the
"main" Route Table of a VPC. This means that the Route Table will be
used for any subnets within the VPC without an explicit Route Table
assigned [1].

This is particularly useful in getting an Internet Gateway in place as
the default for a VPC, since the automatically created Main Route Table
does not have one [2].

Note that this resource is an abstraction over an association and does not
map directly to a CRUD-able object in AWS. In order to retain a coherent
"Delete" operation for this resource, we remember the ID of the AWS-created
Route Table and reset the VPC's main Route Table to it when this
resource is deleted.

refs #843, #748

[1] http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Route_Tables.html#RouteTableDetails
[2] http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Internet_Gateway.html#Add_IGW_Routing

[phinze]

Ok paging @mitchellh for review. Happy to walk you through it synchronously if that would be helpful.

Working on docs now.

[phinze]

@mitchellh ^^ this limitation of the current terraform graph is worth noting. AFAICT there's currently no way of expressing the required order of operations to make this possible

[mitchellh]

I think this relates back to that same issue of implicit deps...

[phinze]

Yep exactly. Will be an interesting problem to solve! 💭

[mitchellh]

This is actually perfect. Great job 👍 MERGE.

[phinze]

[ptrkdy]

I was stuck on topic this and found the solution in this PR before I found the documentation (which is my own fault admittedly), but I would like to leave a bread crumb for the next person who might be searching for this.

https://www.terraform.io/docs/providers/aws/r/main_route_table_assoc.html
together with
https://www.terraform.io/docs/providers/aws/r/route_table.html

Yields something along the lines of the below (as of version 0.9.2):

---

resource "aws_route_table" "main_dev" {
vpc_id = "${aws_vpc.main.id}"
route {
cidr_block = "0.0.0.0/0"
gateway_id = "${aws_internet_gateway.dev_igw.id}"
}
tags {
Name = "main"
}
}

resource "aws_main_route_table_association" "main_dev" {
vpc_id = "${aws_vpc.main.id}"
route_table_id = "${aws_route_table.main_dev.id}"
}

---

When the main route column in the AWS console updated to 'Yes' it gave me a smile!

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