Add ControllerGetNodeInfo and NodeGetID RPCs (alpha)

This proposal adds two new RPCs to enable node registration without
requiring cloud API credentials on the node side:

- NodeGetID: Returns only the node identifier, which can be obtained
  locally (e.g., from instance metadata) without cloud API access.

- ControllerGetNodeInfo: Fetches node topology and max_volumes_per_node
  from the controller side, where cloud API credentials are available.

New capabilities:
- NodeServiceCapability.RPC.GET_ID
- ControllerServiceCapability.RPC.GET_NODE_INFO

Key design decisions:
- If SP supports GET_ID, it MUST also support GET_NODE_INFO
- published_volume_ids field allows accurate calculation of remaining
  attachable volumes by distinguishing CSI-managed vs non-CSI volumes
- Both RPCs are marked as alpha

This addresses security requirements where cloud API credentials should
not be distributed to node components.

Signed-off-by: 胡玮文 <huweiwen.hww@alibaba-inc.com>

Author: huww98

csi.proto

@@ -110,6 +110,11 @@ service Controller {
   rpc ControllerModifyVolume (ControllerModifyVolumeRequest)
     returns (ControllerModifyVolumeResponse) {
     }
+
+  rpc ControllerGetNodeInfo (ControllerGetNodeInfoRequest)
+    returns (ControllerGetNodeInfoResponse) {
+        option (alpha_method) = true;
+    }
 }
 
 service GroupController {
@@ -167,6 +172,11 @@ service Node {
 
   rpc NodeGetInfo (NodeGetInfoRequest)
     returns (NodeGetInfoResponse) {}
+
+  rpc NodeGetID (NodeGetIDRequest)
+    returns (NodeGetIDResponse) {
+        option (alpha_method) = true;
+    }
 }
 message GetPluginInfoRequest {
   // Intentionally empty.
@@ -1043,6 +1053,55 @@ message ControllerModifyVolumeRequest {
 message ControllerModifyVolumeResponse {
 }
 
+message ControllerGetNodeInfoRequest {
+  // The identifier of the node as understood by the SP.
+  // This field is REQUIRED.
+  // This field MUST match the node_id returned by `NodeGetInfo` or
+  // `NodeGetID`.
+  // This field overrides the general CSI size limit.
+  // The size of this field SHALL NOT exceed 256 bytes.
+  string node_id = 1;
+
+  // The volume IDs that the CO believes are currently published to this
+  // node. This field is OPTIONAL.
+  // This SHOULD include all volumes that the CO considers published,
+  // including those with uncertain status (e.g., publish RPC failed).
+  // The SP MAY use this information to calculate the maximum number
+  // of volumes that can be published to the node.
+  // For example, if the node has a maximum of 16 publishable volumes
+  // and 10 volumes are already published, but only 8 reported by the
+  // CO, then the SP SHOULD infer that the remaining 2 volumes are not
+  // managed by CSI and only report 14 max_volumes_per_node.
+  repeated string published_volume_ids = 2;
+}
+
+message ControllerGetNodeInfoResponse {
+  // Maximum number of volumes that controller can publish to the node.
+  // If value is not set or zero CO SHALL decide how many volumes of
+  // this type can be published by the controller to the node. The
+  // plugin MUST NOT set negative values here.
+  // This field is OPTIONAL.
+  int64 max_volumes_per_node = 1;
+
+  // Specifies where (regions, zones, racks, etc.) the node is
+  // accessible from.
+  // A plugin that returns this field MUST also set the
+  // VOLUME_ACCESSIBILITY_CONSTRAINTS plugin capability.
+  // COs MAY use this information along with the topology information
+  // returned in CreateVolumeResponse to ensure that a given volume is
+  // accessible from a given node when scheduling workloads.
+  // This field is OPTIONAL. If it is not specified, the CO MAY assume
+  // the node is not subject to any topological constraint, and MAY
+  // schedule workloads that reference any volume V, such that there are
+  // no topological constraints declared for V.
+  //
+  // Example 1:
+  //   accessible_topology =
+  //     {"region": "R1", "zone": "Z2"}
+  // Indicates the node exists within the "region" "R1" and the "zone"
+  // "Z2".
+  Topology accessible_topology = 2;
+}
 message GetCapacityRequest {
   // If specified, the Plugin SHALL report the capacity of the storage
   // that can be used to provision volumes that satisfy ALL of the
@@ -1190,6 +1249,12 @@ message ControllerServiceCapability {
       // Indicates the SP supports the GetSnapshot RPC.
       // This enables COs to fetch an existing snapshot.
       GET_SNAPSHOT = 15 [(alpha_enum_value) = true];
+
+      // Indicates the SP supports the ControllerGetNodeInfo RPC.
+      // This enables COs to fetch node topology and capacity
+      // information from the controller side, avoiding the need for
+      // cloud API credentials on the node side.
+      GET_NODE_INFO = 16 [(alpha_enum_value) = true];
     }
 
     Type type = 1;
@@ -1672,6 +1737,15 @@ message NodeServiceCapability {
       // with provided volume group identifier during node stage
       // or node publish RPC calls.
       VOLUME_MOUNT_GROUP = 6;
+
+      // Indicates the SP supports the NodeGetID RPC.
+      // This enables COs to fetch only the node identifier from
+      // the node side without requiring cloud API credentials.
+      // The topology and capacity information can then be fetched
+      // via ControllerGetNodeInfo.
+      // If the SP supports GET_ID, it MUST also support
+      // GET_NODE_INFO controller capability.
+      GET_ID = 7 [(alpha_enum_value) = true];
     }
 
     Type type = 1;
@@ -1726,6 +1800,26 @@ message NodeGetInfoResponse {
   // "Z2".
   Topology accessible_topology = 3;
 }
+message NodeGetIDRequest {
+  // Intentionally empty.
+}
+
+message NodeGetIDResponse {
+  // The identifier of the node as understood by the SP.
+  // This field is REQUIRED.
+  // This field MUST contain enough information to uniquely identify
+  // this specific node vs all other nodes supported by this plugin.
+  // This field SHALL be used by the CO in subsequent calls, including
+  // `ControllerPublishVolume` and `ControllerGetNodeInfo`, to refer to
+  // this node.
+  // The SP is NOT responsible for global uniqueness of node_id across
+  // multiple SPs.
+  // This field overrides the general CSI size limit.
+  // The size of this field SHALL NOT exceed 256 bytes. The general
+  // CSI size limit, 128 byte, is RECOMMENDED for best backwards
+  // compatibility.
+  string node_id = 1;
+}
 message NodeExpandVolumeRequest {
   // The ID of the volume. This field is REQUIRED.
   string volume_id = 1;