feat(ctl): define initial structure for load balancer

ctl/src/balancer/mod.rs

@@ -0,0 +1,44 @@
+#![allow(dead_code)]
+
+use std::{
+    collections::HashMap,
+    net::SocketAddr
+};
+
+use axum::extract::Request;
+use proto::common::instance::InstanceId;
+use proto::common::service::ServiceId;
+
+struct Balancer<S> {
+    strategy: S,
+    addrs: HashMap<ServiceId, Vec<(InstanceId, SocketAddr)>>
+}
+
+trait Strategy {
+    async fn get_server(&self, _req: &Request) -> (InstanceId, SocketAddr);
+}
+
+impl<S> Balancer<S>
+where
+    S: Strategy
+{
+    pub async fn run() {
+        todo!();
+    }
+
+    async fn next_server(&self, _req: &Request) -> (InstanceId, SocketAddr) {
+        todo!();
+    }
+
+    pub async fn drop_instance(&self, _id: InstanceId) {
+        todo!();
+    }
+
+    pub async fn add_instance(&self, _id: InstanceId, _at: SocketAddr) {
+        todo!();
+    }
+
+    pub async fn swap_instance(_old_id: InstanceId, _new_id: InstanceId, _new_at: SocketAddr) {
+        todo!();
+    }
+}

ctl/src/main.rs

@@ -4,6 +4,7 @@ use crate::{discovery::Discovery, http::HttpState};
 
 mod discovery;
 mod http;
+mod balancer;
 
 #[tokio::main]
 async fn main() {