Subordinate charm config PoC

charms/worker/k8s/charmcraft.yaml

@@ -126,7 +126,7 @@ config:
       type: string
       description: |
         Labels can be used to organize and to select subsets of nodes in the
-        cluster. Declare node labels in key=value format, separated by spaces.      
+        cluster. Declare node labels in key=value format, separated by spaces.
     register-with-taints:
       type: string
       default: ""
@@ -178,6 +178,9 @@ provides:
     interface: containerd
   ceph-k8s-info:
     interface: kubernetes-info
+  feature:
+    interface: k8s-snap-feature
+    scope: container
 
 requires:
   etcd:

charms/worker/k8s/lib/charms/k8s/v0/k8sd_api_manager.py

@@ -35,7 +35,7 @@ class utilises different connection factories (UnixSocketConnectionFactory
 from typing import Any, Dict, Generator, List, Optional, Type, TypeVar
 
 import yaml
-from pydantic import AnyHttpUrl, BaseModel, Field, SecretStr, validator
+from pydantic import AnyHttpUrl, BaseModel, Field, SecretStr, validator, root_validator
 
 # The unique Charmhub library identifier, never change it
 LIBID = "6a5f235306864667a50437c08ba7e83f"
@@ -520,6 +520,27 @@ class KubeConfigMetadata(BaseModel):
 
     kubeconfig: str
 
+class FeatureRelationData(BaseModel):
+    """Model representing data for a feature relation.
+
+    Attributes:
+        name (str): The feature name.
+        version (str): The library version that was used to create the feature object.
+        attributes (str): The serialized Pydantic model representing the feature configuration.
+    """
+    name: str
+    version: str
+    attributes: str
+
+    @root_validator(pre=True)
+    def check_data(cls, values):
+        if 'name' not in values:
+            raise ValueError("The 'name' field must be provided")
+        if 'version' not in values:
+            raise ValueError("The 'version' field must be provided")
+        if 'attributes' not in values:
+            raise ValueError("The 'attributes' field must be provided")
+        return values
 
 class GetKubeConfigResponse(BaseRequestModel):
     """Response model for getting the kubeconfig from the cluster.

charms/worker/k8s/src/charm.py

@@ -21,6 +21,7 @@
 import socket
 import subprocess
 import uuid
+import json
 from functools import cached_property
 from pathlib import Path
 from time import sleep
@@ -38,6 +39,7 @@
 from charms.interface_external_cloud_provider import ExternalCloudProvider
 from charms.k8s.v0.k8sd_api_manager import (
     BootstrapConfig,
+    LoadBalancerConfig,
     ControlPlaneNodeJoinConfig,
     CreateClusterRequest,
     DNSConfig,
@@ -51,6 +53,7 @@
     UpdateClusterConfigRequest,
     UserFacingClusterConfig,
     UserFacingDatastoreConfig,
+    FeatureRelationData,
 )
 from charms.kubernetes_libs.v0.etcd import EtcdReactiveRequires
 from charms.node_base import LabelMaker
@@ -60,6 +63,7 @@
 from snap import version as snap_version
 from token_distributor import ClusterTokenType, TokenCollector, TokenDistributor, TokenStrategy
 from typing_extensions import Literal
+from pydantic import ValidationError
 
 # Log messages can be retrieved using juju debug-log
 log = logging.getLogger(__name__)
@@ -149,10 +153,48 @@ def __init__(self, *args):
         )
 
         self.framework.observe(self.on.update_status, self._on_update_status)
+
         if self.is_control_plane:
             self.etcd = EtcdReactiveRequires(self)
             self.framework.observe(self.on.get_kubeconfig_action, self._get_external_kubeconfig)
 
+    def _resolve_feature_relations(self, event: ops.EventBase):
+        log.info("Resolving feature relations as snap configuration")
+
+        for relation in self.model.relations["feature"]:
+            for unit in relation.units:
+                raw_relation_data = relation.data[unit]
+
+                if not raw_relation_data:
+                    log.warning("No relation data found for %s relation", relation.name)
+                    continue
+
+                try:
+                    parsed_relation_data = FeatureRelationData.parse_obj(raw_relation_data)
+                except ValidationError as e:
+                    log.warning("The relation data for %s relation is not valid: %s", relation.name, e)
+                    continue
+
+                feature_name = parsed_relation_data.name
+                feature_attributes = parsed_relation_data.attributes
+
+                feature_config_classes: Dict[str, type] = {
+                    "load-balancer": LoadBalancerConfig,
+                    "local-storage": LocalStorageConfig,
+                }
+                if not (config_class := feature_config_classes.get(feature_name)):
+                    status.add(ops.BlockedStatus(f"Unsupported feature {feature_name}"))
+                    continue
+
+                feature_config = config_class.parse_raw(feature_attributes)
+                log.info("Updating feature [%s] with config [%s]", feature_name, feature_config)
+
+                cluster_config = UserFacingClusterConfig(**{feature_name: feature_config})
+                update_request = UpdateClusterConfigRequest(config=cluster_config)
+                self.api_manager.update_cluster_config(update_request)
+
+                log.info("Feature [%s] updated", feature_name)
+
     def _k8s_info(self, event: ops.EventBase):
         """Send cluster information on the kubernetes-info relation.
 
@@ -700,6 +742,7 @@ def _reconcile(self, event: ops.EventBase):
             self._apply_cos_requirements()
             self._revoke_cluster_tokens(event)
             self._ensure_cluster_config()
+            self._resolve_feature_relations(event)
         self._join_cluster()
         self._config_containerd_registries()
         self._configure_cos_integration()