add option to pass in anchors

paasta_tools/contrib/service_shard_update.py

@@ -2,6 +2,9 @@
 import logging
 import sys
 
+from ruamel.yaml.comments import CommentedMap
+from ruamel.yaml.comments import CommentedSeq
+
 from paasta_tools.cli.utils import trigger_deploys
 from paasta_tools.config_utils import AutoConfigUpdater
 from paasta_tools.utils import DEFAULT_SOA_CONFIGS_GIT_URL
@@ -164,6 +167,15 @@ def parse_args():
         type=int,
         dest="autotune_max_disk",
     )
+    parser.add_argument(
+        "--anchor",
+        dest="anchors",
+        help="Additional configuration to add to the service shard (YAML anchor names)",
+        action="append",
+        type=str,
+        default=[],
+        required=False,
+    )
     return parser.parse_args()
 
 
@@ -306,6 +318,19 @@ def main(args):
                     # Add the missing definition and write to the corresponding config
                     if args.shard_name not in config_file.keys():
                         config_file[args.shard_name] = instance_config
+
+                        # Finally, add any YAML anchors to the service shard configuration
+                        if len(args.anchors) > 0:
+                            configWithAnchor = CommentedMap({
+                                '<<': CommentedSeq(
+                                    [config_file[anchor] for anchor in args.anchors if anchor in config_file.keys()]
+                                )
+                            })
+                            # set the formatting to single line for readability
+                            configWithAnchor["<<"].fa.set_flow_style()
+                            configWithAnchor.update(config_file[args.shard_name])
+                            config_file[args.shard_name] = configWithAnchor
+
                         updater.write_configs(
                             args.service, f"{config_prefix}{config_path}", config_file
                         )