feat: node excluder (#5964)

* feat: node excluder

* fix ci

* fix ci

src/meta-srv/src/lib.rs

@@ -31,6 +31,7 @@ pub mod metasrv;
 pub mod metrics;
 #[cfg(feature = "mock")]
 pub mod mocks;
+pub mod node_excluder;
 pub mod procedure;
 pub mod pubsub;
 pub mod region;

src/meta-srv/src/node_excluder.rs

@@ -0,0 +1,26 @@
+// Copyright 2023 Greptime Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::sync::Arc;
+
+use common_meta::DatanodeId;
+
+pub type NodeExcluderRef = Arc<dyn NodeExcluder>;
+
+/// [NodeExcluder] is used to help decide whether some nodes should be excluded (out of consideration)
+/// in certain situations. For example, in some node selectors.
+pub trait NodeExcluder: Send + Sync {
+    /// Returns the excluded datanode ids.
+    fn excluded_datanode_ids(&self) -> &Vec<DatanodeId>;
+}