ENH gets latest image if more than one (#472)

* enable getting the newest image if there are more than one with the same string contained in the name

* cleanup

* cleanup

* clean up

* typo

* update the tests

Author: maikia

ramp-engine/ramp_engine/aws/api.py

@@ -251,26 +251,25 @@ def launch_ec2_instances(config, nb=1):
 def _get_image_id(config, image_name):
     sess = _get_boto_session(config)
     client = sess.client('ec2')
+
+    # get all the images with the given image_name in the name
     result = client.describe_images(Filters=[
         {
             'Name': 'name',
-            'Values': [
-                image_name
-            ]
+            'Values': [f'{image_name}*'
+                       ],
         }
     ])
+
     images = result['Images']
     if len(images) == 0:
         raise ValueError(
             'No image corresponding to the name "{}"'.format(image_name))
-    elif len(images) > 1:
-        raise ValueError(
-            'Multiple images corresponding to the name "{}".'
-            ' Please fix that'.format(image_name))
-    else:
-        image = images[0]
-        image_id = image['ImageId']
-        return image_id
+
+    # get only the newest image if there are more than one
+    image = sorted(images, key=lambda x: x['CreationDate'],
+                   reverse=True)[0]
+    return image['ImageId']
 
 
 def terminate_ec2_instance(config, instance_id):

ramp-engine/ramp_engine/tests/test_aws.py

@@ -191,7 +191,7 @@ def test_launch_ec2_instances(boto_session_cls, use_spot_instance):
     session = boto_session_cls.return_value
     client = session.client.return_value
     describe_images = client.describe_images
-    images = {"Images": [{"ImageId": 1}]}
+    images = {"Images": [{"ImageId": 1, "CreationDate": 123}]}
     describe_images.return_value = images
     config = read_config(os.path.join(HERE, '_aws_config.yml'))
 
@@ -218,7 +218,7 @@ def test_creating_instances(boto_session_cls, caplog,
     session = boto_session_cls.return_value
     client = session.client.return_value
     describe_images = client.describe_images
-    images = {"Images": [{"ImageId": 1}]}
+    images = {"Images": [{"ImageId": 1, "CreationDate": 123}]}
     describe_images.return_value = images
 
     error = {