automation: move image operations to own functions

An upcoming commit will need this functionality with slightly different
values and it is enough code to not want to duplicate. Let's refactor
into standalone functions so it can be reused.

Differential Revision: https://phab.mercurial-scm.org/D6318

contrib/automation/hgautomation/aws.py

@@ -402,14 +402,14 b' def ensure_iam_state(iamclient, iamresou'
             profile.add_role(RoleName=role)
 
 
-def find_windows_server_2019_image(ec2resource):
-    """Find the Amazon published Windows Server 2019 base image."""
+def find_image(ec2resource, owner_id, name):
+    """Find an AMI by its owner ID and name."""
 
     images = ec2resource.images.filter(
         Filters=[
             {
-                'Name': 'owner-alias',
-                'Values': ['amazon'],
+                'Name': 'owner-id',
+                'Values': [owner_id],
             },
             {
                 'Name': 'state',
@@ -421,14 +421,14 b' def find_windows_server_2019_image(ec2re'
             },
             {
                 'Name': 'name',
-                'Values': ['Windows_Server-2019-English-Full-Base-2019.02.13'],
+                'Values': [name],
             },
         ])
 
     for image in images:
         return image
 
-    raise Exception('unable to find Windows Server 2019 image')
+    raise Exception('unable to find image for %s' % name)
 
 
 def ensure_security_groups(ec2resource, prefix='hg-'):
@@ -684,6 +684,84 b' def create_temp_windows_ec2_instances(c:'
         yield instances
 
 
+def resolve_fingerprint(fingerprint):
+    fingerprint = json.dumps(fingerprint, sort_keys=True)
+    return hashlib.sha256(fingerprint.encode('utf-8')).hexdigest()
+
+
+def find_and_reconcile_image(ec2resource, name, fingerprint):
+    """Attempt to find an existing EC2 AMI with a name and fingerprint.
+
+    If an image with the specified fingerprint is found, it is returned.
+    Otherwise None is returned.
+
+    Existing images for the specified name that don't have the specified
+    fingerprint or are missing required metadata or deleted.
+    """
+    # Find existing AMIs with this name and delete the ones that are invalid.
+    # Store a reference to a good image so it can be returned one the
+    # image state is reconciled.
+    images = ec2resource.images.filter(
+        Filters=[{'Name': 'name', 'Values': [name]}])
+
+    existing_image = None
+
+    for image in images:
+        if image.tags is None:
+            print('image %s for %s lacks required tags; removing' % (
+                image.id, image.name))
+            remove_ami(ec2resource, image)
+        else:
+            tags = {t['Key']: t['Value'] for t in image.tags}
+
+            if tags.get('HGIMAGEFINGERPRINT') == fingerprint:
+                existing_image = image
+            else:
+                print('image %s for %s has wrong fingerprint; removing' % (
+                      image.id, image.name))
+                remove_ami(ec2resource, image)
+
+    return existing_image
+
+
+def create_ami_from_instance(ec2client, instance, name, description,
+                             fingerprint):
+    """Create an AMI from a running instance.
+
+    Returns the ``ec2resource.Image`` representing the created AMI.
+    """
+    instance.stop()
+
+    ec2client.get_waiter('instance_stopped').wait(
+        InstanceIds=[instance.id],
+        WaiterConfig={
+            'Delay': 5,
+        })
+    print('%s is stopped' % instance.id)
+
+    image = instance.create_image(
+        Name=name,
+        Description=description,
+    )
+
+    image.create_tags(Tags=[
+        {
+            'Key': 'HGIMAGEFINGERPRINT',
+            'Value': fingerprint,
+        },
+    ])
+
+    print('waiting for image %s' % image.id)
+
+    ec2client.get_waiter('image_available').wait(
+        ImageIds=[image.id],
+    )
+
+    print('image %s available as %s' % (image.id, image.name))
+
+    return image
+
+
 def ensure_windows_dev_ami(c: AWSConnection, prefix='hg-'):
     """Ensure Windows Development AMI is available and up-to-date.
 
@@ -702,6 +780,10 b' def ensure_windows_dev_ami(c: AWSConnect'
 
     name = '%s%s' % (prefix, 'windows-dev')
 
+    image = find_image(ec2resource,
+                       '801119661308',
+                       'Windows_Server-2019-English-Full-Base-2019.02.13')
+
     config = {
         'BlockDeviceMappings': [
             {
@@ -713,7 +795,7 b' def ensure_windows_dev_ami(c: AWSConnect'
                 },
             }
         ],
-        'ImageId': find_windows_server_2019_image(ec2resource).id,
+        'ImageId': image.id,
         'InstanceInitiatedShutdownBehavior': 'stop',
         'InstanceType': 't3.medium',
         'KeyName': '%sautomation' % prefix,
@@ -748,38 +830,14 b' def ensure_windows_dev_ami(c: AWSConnect'
 
     # Compute a deterministic fingerprint to determine whether image needs
     # to be regenerated.
-    fingerprint = {
+    fingerprint = resolve_fingerprint({
         'instance_config': config,
         'user_data': WINDOWS_USER_DATA,
         'initial_bootstrap': WINDOWS_BOOTSTRAP_POWERSHELL,
         'bootstrap_commands': commands,
-    }
-
-    fingerprint = json.dumps(fingerprint, sort_keys=True)
-    fingerprint = hashlib.sha256(fingerprint.encode('utf-8')).hexdigest()
-
-    # Find existing AMIs with this name and delete the ones that are invalid.
-    # Store a reference to a good image so it can be returned one the
-    # image state is reconciled.
-    images = ec2resource.images.filter(
-        Filters=[{'Name': 'name', 'Values': [name]}])
-
-    existing_image = None
+    })
 
-    for image in images:
-        if image.tags is None:
-            print('image %s for %s lacks required tags; removing' % (
-                image.id, image.name))
-            remove_ami(ec2resource, image)
-        else:
-            tags = {t['Key']: t['Value'] for t in image.tags}
-
-            if tags.get('HGIMAGEFINGERPRINT') == fingerprint:
-                existing_image = image
-            else:
-                print('image %s for %s has wrong fingerprint; removing' % (
-                      image.id, image.name))
-                remove_ami(ec2resource, image)
+    existing_image = find_and_reconcile_image(ec2resource, name, fingerprint)
 
     if existing_image:
         return existing_image
@@ -839,36 +897,9 b' def ensure_windows_dev_ami(c: AWSConnect'
         run_powershell(instance.winrm_client, '\n'.join(commands))
 
         print('bootstrap completed; stopping %s to create image' % instance.id)
-        instance.stop()
-
-        ec2client.get_waiter('instance_stopped').wait(
-            InstanceIds=[instance.id],
-            WaiterConfig={
-                'Delay': 5,
-            })
-        print('%s is stopped' % instance.id)
-
-        image = instance.create_image(
-            Name=name,
-            Description='Mercurial Windows development environment',
-        )
-
-        image.create_tags(Tags=[
-            {
-                'Key': 'HGIMAGEFINGERPRINT',
-                'Value': fingerprint,
-            },
-        ])
-
-        print('waiting for image %s' % image.id)
-
-        ec2client.get_waiter('image_available').wait(
-            ImageIds=[image.id],
-        )
-
-        print('image %s available as %s' % (image.id, image.name))
-
-        return image
+        return create_ami_from_instance(ec2client, instance, name,
+                                        'Mercurial Windows development environment',
+                                        fingerprint)
 
 
 @contextlib.contextmanager