provider/aws: Add support for restoring from Redis backup stored in S3

Fixes #2377

builtin/providers/aws/resource_aws_elasticache_cluster.go

@@ -105,6 +105,22 @@ func resourceAwsElasticacheCluster() *schema.Resource {
 				},
 			},
 
+			// A single-element string list containing an Amazon Resource Name (ARN) that
+			// uniquely identifies a Redis RDB snapshot file stored in Amazon S3. The snapshot
+			// file will be used to populate the node group.
+			//
+			// See also:
+			// https://github.com/aws/aws-sdk-go/blob/4862a174f7fc92fb523fc39e68f00b87d91d2c3d/service/elasticache/api.go#L2079
+			"snapshot_arns": &schema.Schema{
+				Type:     schema.TypeSet,
+				Optional: true,
+				ForceNew: true,
+				Elem:     &schema.Schema{Type: schema.TypeString},
+				Set: func(v interface{}) int {
+					return hashcode.String(v.(string))
+				},
+			},
+
 			"tags": tagsSchema(),
 
 			// apply_immediately is used to determine when the update modifications
@@ -154,6 +170,13 @@ func resourceAwsElasticacheClusterCreate(d *schema.ResourceData, meta interface{
 		req.CacheParameterGroupName = aws.String(v.(string))
 	}
 
+	snaps := d.Get("snapshot_arns").(*schema.Set).List()
+	if len(snaps) > 0 {
+		s := expandStringList(snaps)
+		req.SnapshotARNs = s
+		log.Printf("[DEBUG] Restoring Redis cluster from S3 snapshot: %#v", s)
+	}
+
 	_, err := conn.CreateCacheCluster(req)
 	if err != nil {
 		return fmt.Errorf("Error creating Elasticache: %s", err)

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

@@ -65,6 +65,10 @@ names to associate with this cache cluster
      `false`. See [Amazon ElastiCache Documentation for more information.][1]
      (Available since v0.6.0)
 
+* `snapshot_arns` – (Optional) A single-element string list containing an 
+Amazon Resource Name (ARN) of a Redis RDB snapshot file stored in Amazon S3. 
+Example: `arn:aws:s3:::my_bucket/snapshot1.rdb`
+
 * `tags` - (Optional) A mapping of tags to assign to the resource.