Use snapshot size if you don't specify a VolumeSize

builder/amazon/common/block_device.go

@@ -32,7 +32,6 @@ func buildBlockDevices(b []BlockDevice) []*ec2.BlockDeviceMapping {
 	for _, blockDevice := range b {
 		ebsBlockDevice := &ec2.EBSBlockDevice{
 			VolumeType:          aws.String(blockDevice.VolumeType),
-			VolumeSize:          aws.Long(blockDevice.VolumeSize),
 			DeleteOnTermination: aws.Boolean(blockDevice.DeleteOnTermination),
 		}
 
@@ -48,6 +47,11 @@ func buildBlockDevices(b []BlockDevice) []*ec2.BlockDeviceMapping {
 			ebsBlockDevice.Encrypted = aws.Boolean(blockDevice.Encrypted)
 		}
 
+		// Use snapshot size if you don't specify a VolumeSize
+		if blockDevice.VolumeSize != 0 {
+			ebsBlockDevice.VolumeSize = aws.Long(blockDevice.VolumeSize)
+		}
+
 		mapping := &ec2.BlockDeviceMapping{
 			DeviceName:  aws.String(blockDevice.DeviceName),
 			VirtualName: aws.String(blockDevice.VirtualName),

builder/amazon/common/block_device_test.go

@@ -81,6 +81,22 @@ func TestBlockDevice(t *testing.T) {
 				VirtualName: aws.String("ephemeral0"),
 			},
 		},
+		{
+			Config: &BlockDevice{
+				DeviceName:          "/dev/sdb",
+				VolumeType:          "standard",
+				DeleteOnTermination: true,
+			},
+
+			Result: &ec2.BlockDeviceMapping{
+				DeviceName:  aws.String("/dev/sdb"),
+				VirtualName: aws.String(""),
+				EBS: &ec2.EBSBlockDevice{
+					VolumeType:          aws.String("standard"),
+					DeleteOnTermination: aws.Boolean(true),
+				},
+			},
+		},
 	}
 
 	for _, tc := range cases {