Allow filtering of aws_subnet_ids by tags

This is the minimal amount of work needed to be able to create a list of a subset of subnet IDs in a VPC, allowing people to loop through them easily when creating EC2 instances or provide a list straight to an ELB.

builtin/providers/aws/data_source_aws_subnet_ids.go

@@ -12,10 +12,14 @@ func dataSourceAwsSubnetIDs() *schema.Resource {
 	return &schema.Resource{
 		Read: dataSourceAwsSubnetIDsRead,
 		Schema: map[string]*schema.Schema{
+
+			"tags": tagsSchemaComputed(),
+
 			"vpc_id": &schema.Schema{
 				Type:     schema.TypeString,
 				Required: true,
 			},
+
 			"ids": &schema.Schema{
 				Type:     schema.TypeSet,
 				Computed: true,
@@ -37,6 +41,10 @@ func dataSourceAwsSubnetIDsRead(d *schema.ResourceData, meta interface{}) error
 		},
 	)
 
+	req.Filters = append(req.Filters, buildEC2TagFilterList(
+		tagsFromMap(d.Get("tags").(map[string]interface{})),
+	)...)
+
 	log.Printf("[DEBUG] DescribeSubnets %s\n", req)
 	resp, err := conn.DescribeSubnets(req)
 	if err != nil {

builtin/providers/aws/data_source_aws_subnet_ids_test.go

@@ -21,7 +21,8 @@ func TestAccDataSourceAwsSubnetIDs(t *testing.T) {
 			{
 				Config: testAccDataSourceAwsSubnetIDsConfigWithDataSource(rInt),
 				Check: resource.ComposeTestCheckFunc(
-					resource.TestCheckResourceAttr("data.aws_subnet_ids.selected", "ids.#", "1"),
+					resource.TestCheckResourceAttr("data.aws_subnet_ids.selected", "ids.#", "3"),
+					resource.TestCheckResourceAttr("data.aws_subnet_ids.private", "ids.#", "2"),
 				),
 			},
 		},
@@ -39,20 +40,50 @@ func testAccDataSourceAwsSubnetIDsConfigWithDataSource(rInt int) string {
 	  }
 	}
 
-	resource "aws_subnet" "test" {
+	resource "aws_subnet" "test_public_a" {
 	  vpc_id            = "${aws_vpc.test.id}"
 	  cidr_block        = "172.%d.123.0/24"
 	  availability_zone = "us-west-2a"
 
 	  tags {
-	    Name = "terraform-testacc-subnet-ids-data-source"
+	    Name = "terraform-testacc-subnet-ids-data-source-public-a"
+			Tier = "Public"
+	  }
+	}
+
+	resource "aws_subnet" "test_private_a" {
+	  vpc_id            = "${aws_vpc.test.id}"
+	  cidr_block        = "172.%d.125.0/24"
+	  availability_zone = "us-west-2a"
+
+	  tags {
+	    Name = "terraform-testacc-subnet-ids-data-source-private-a"
+			Tier = "Private"
+	  }
+	}
+
+	resource "aws_subnet" "test_private_b" {
+	  vpc_id            = "${aws_vpc.test.id}"
+	  cidr_block        = "172.%d.126.0/24"
+	  availability_zone = "us-west-2b"
+
+	  tags {
+	    Name = "terraform-testacc-subnet-ids-data-source-private-b"
+			Tier = "Private"
 	  }
 	}
 
 	data "aws_subnet_ids" "selected" {
 	  vpc_id = "${aws_vpc.test.id}"
 	}
-	`, rInt, rInt)
+
+	data "aws_subnet_ids" "private" {
+		vpc_id = "${aws_vpc.test.id}"
+		tags {
+			Tier = "Private"
+		}
+	}
+	`, rInt, rInt, rInt, rInt)
 }
 
 func testAccDataSourceAwsSubnetIDsConfig(rInt int) string {
@@ -65,14 +96,37 @@ func testAccDataSourceAwsSubnetIDsConfig(rInt int) string {
 		  }
 		}
 
-		resource "aws_subnet" "test" {
+		resource "aws_subnet" "test_public_a" {
 		  vpc_id            = "${aws_vpc.test.id}"
 		  cidr_block        = "172.%d.123.0/24"
 		  availability_zone = "us-west-2a"
 
 		  tags {
-		    Name = "terraform-testacc-subnet-ids-data-source"
+		    Name = "terraform-testacc-subnet-ids-data-source-public-a"
+				Tier = "Public"
 		  }
 		}
-		`, rInt, rInt)
+
+		resource "aws_subnet" "test_private_a" {
+		  vpc_id            = "${aws_vpc.test.id}"
+		  cidr_block        = "172.%d.125.0/24"
+		  availability_zone = "us-west-2a"
+
+		  tags {
+		    Name = "terraform-testacc-subnet-ids-data-source-private-a"
+				Tier = "Private"
+		  }
+		}
+
+		resource "aws_subnet" "test_private_b" {
+		  vpc_id            = "${aws_vpc.test.id}"
+		  cidr_block        = "172.%d.126.0/24"
+		  availability_zone = "us-west-2b"
+
+		  tags {
+		    Name = "terraform-testacc-subnet-ids-data-source-private-b"
+				Tier = "Private"
+		  }
+		}
+		`, rInt, rInt, rInt, rInt)
 }

website/source/docs/providers/aws/d/subnet_ids.html.markdown

@@ -31,10 +31,33 @@ output "subnet_cidr_blocks" {
 }
 ```
 
+The following example retrieves a list of all subnets in a VPC with a custom
+tag of `Tier` set to a value of "Private" so that the `aws_instance` resource
+can loop through the subnets, putting instances across availability zones.
+
+```hcl
+data "aws_subnet_ids" "private" {
+  vpc_id = "${var.vpc_id}"
+  tags {
+    Tier = "Private"
+  }
+}
+
+resource "aws_instance" "app" {
+  count         = "3"
+  ami           = "${var.ami}"
+  instance_type = "t2.micro"
+  subnet_id     = "${element(data.aws_subnet_ids.private.ids, count.index)}"
+}
+```
+
 ## Argument Reference
 
 * `vpc_id` - (Required) The VPC ID that you want to filter from.
 
+* `tags` - (Optional) A mapping of tags, each pair of which must exactly match
+  a pair on the desired subnets.
+
 ## Attributes Reference
 
 * `ids` - Is a list of all the subnet ids found. If none found. This data source will fail out.