aws_elasticache_subnet_group normalizes name to lowercase.

builtin/providers/aws/resource_aws_elasticache_subnet_group.go

@@ -3,6 +3,7 @@ package aws
 import (
 	"fmt"
 	"log"
+	"strings"
 	"time"
 
 	"github.com/aws/aws-sdk-go/aws"
@@ -29,6 +30,12 @@ func resourceAwsElasticacheSubnetGroup() *schema.Resource {
 				Type:     schema.TypeString,
 				Required: true,
 				ForceNew: true,
+				StateFunc: func(val interface{}) string {
+					// Elasticache normalizes subnet names to lowercase,
+					// so we have to do this too or else we can end up
+					// with non-converging diffs.
+					return strings.ToLower(val.(string))
+				},
 			},
 			"subnet_ids": &schema.Schema{
 				Type:     schema.TypeSet,
@@ -66,7 +73,10 @@ func resourceAwsElasticacheSubnetGroupCreate(d *schema.ResourceData, meta interf
 	}
 
 	// Assign the group name as the resource ID
-	d.SetId(name)
+	// Elasticache always retains the name in lower case, so we have to
+	// mimic that or else we won't be able to refresh a resource whose
+	// name contained uppercase characters.
+	d.SetId(strings.ToLower(name))
 
 	return nil
 }

builtin/providers/aws/resource_aws_elasticache_subnet_group_test.go

@@ -150,7 +150,10 @@ resource "aws_subnet" "foo" {
 }
 
 resource "aws_elasticache_subnet_group" "bar" {
-    name = "tf-test-cache-subnet-%03d"
+    // Including uppercase letters in this name to ensure
+    // that we correctly handle the fact that the API
+    // normalizes names to lowercase.
+    name = "tf-TEST-cache-subnet-%03d"
     description = "tf-test-cache-subnet-group-descr"
     subnet_ids = ["${aws_subnet.foo.id}"]
 }

website/source/docs/providers/aws/r/elasticache_subnet_group.html.markdown

@@ -45,8 +45,8 @@ resource "aws_elasticache_subnet_group" "bar" {
 The following arguments are supported:
 
 * `description` – (Required) Description for the cache subnet group
-* `name` – (Required) Name for the cache subnet group. This value is stored as 
-a lowercase string
+* `name` – (Required) Name for the cache subnet group. Elasticache converts
+  this name to lowercase.
 * `subnet_ids` – (Required) List of VPC Subnet IDs for the cache subnet group
 
 ## Attributes Reference