--- /tmp/orig	2017-08-23 16:19:40.759487634 +0200
+++ /usr/share/foreman/app/models/compute_resources/foreman/model/ec2.rb	2017-08-23 16:20:53.095359813 +0200
@@ -48,6 +48,7 @@
       args[:security_group_ids].reject!(&:empty?) if args.has_key?(:security_group_ids)
       args[:associate_public_ip] = subnet_implies_is_vpc?(args) && args[:managed_ip] == 'public'
       args[:private_ip_address] = args[:interfaces_attributes][:"0"][:ip]
+      args[:block_device_mapping] = [ {:DeviceName => 'xvda', 'Ebs.VolumeSize' => 20 } ]
       super(args)
     rescue Fog::Errors::Error => e
       Foreman::Logging.exception("Unhandled EC2 error", e)