Try using SSD for root volumes.

buildman/manager/executor.py

@@ -113,6 +113,14 @@ class EC2Executor(BuilderExecutor):
     logger.debug('Generated cloud config: %s', user_data)
 
     ec2_conn = self._get_conn()
+
+    ssd_root_ebs = boto.ec2.blockdevicemapping.BlockDeviceType(
+        size=8,
+        volume_type='gp2',
+        delete_on_termination=True,
+    )
+    block_devices = boto.ec2.blockdevicemapping.BlockDeviceMapping()
+    block_devices['/dev/sda1'] = ssd_root_ebs
     reservation = yield From(ec2_conn.run_instances(
         coreos_ami,
         instance_type=self.executor_config['EC2_INSTANCE_TYPE'],
@@ -120,6 +128,7 @@ class EC2Executor(BuilderExecutor):
         key_name=self.executor_config.get('EC2_KEY_NAME', None),
         user_data=user_data,
         instance_initiated_shutdown_behavior='terminate',
+        block_device_map=block_devices,
     ))
 
     if not reservation.instances: