updated the server so that you can set a preferred llm server. It will

attempt to utilze that server for every request unless its not online
then it will fallback to any other online serer.

src/main.rs

@@ -26,7 +26,7 @@ use std::{
 #[command(
     name = "llm-router",
     version,
-    about = "LLM Router Proxy with System Tray and Systemd Integration"
+    about = "LLM Router Proxy with System Tray, Systemd Integration, and Preferred Backend"
 )]
 struct Args {
     /// Run the proxy service in daemon mode (non-interactive, used by systemd)
@@ -46,6 +46,8 @@ struct Args {
 struct Config {
     listen_port: u16,
     backend_urls: Vec<String>,
+    #[serde(default)]
+    preferred_backend: Option<String>,
 }
 
 #[derive(Clone)]
@@ -57,12 +59,15 @@ struct Backend {
 #[derive(Clone)]
 struct AppState {
     backends: Vec<Backend>,
+    preferred_backend: Option<String>,
     client: reqwest::Client,
     counter: Arc<AtomicUsize>,
 }
+
 #[derive(Debug)]
 struct LLMRouterTray {
     backend_data: Vec<(String, bool)>,
+    preferred_url: Option<String>,
 }
 
 impl Tray for LLMRouterTray {
@@ -87,7 +92,9 @@ impl Tray for LLMRouterTray {
             } else {
                 "🔴 Offline"
             };
-            desc.push_str(&format!("• {}: {}\n", url, status));
+            let is_pref = self.preferred_url.as_ref() == Some(url);
+            let pref_tag = if is_pref { " [Preferred]" } else { "" };
+            desc.push_str(&format!("• {}{}: {}\n", url, pref_tag, status));
         }
         ksni::ToolTip {
             title: "LLM Router Status".into(),
@@ -114,9 +121,15 @@ impl Tray for LLMRouterTray {
             } else {
                 "🔴 Offline"
             };
+            let is_pref = self.preferred_url.as_ref() == Some(url);
+            let label = if is_pref {
+                format!("★ {} [{}] (Preferred)", url, status_str)
+            } else {
+                format!("{} [{}]", url, status_str)
+            };
             items.push(
                 StandardItem {
-                    label: format!("{} [{}]", url, status_str),
+                    label,
                     enabled: false,
                     ..Default::default()
                 }
@@ -295,9 +308,26 @@ fn load_config(is_daemon: bool) -> Config {
             backend_urls.push(url);
         }
 
+        let mut preferred_backend = None;
+        if backend_urls.len() > 1 {
+            print!("Enter a preferred backend URL from the list above (leave blank for none): ");
+            io::stdout().flush().unwrap();
+            let mut pref = String::new();
+            io::stdin().read_line(&mut pref).unwrap();
+            let pref = pref.trim().to_string();
+            if !pref.is_empty() {
+                if backend_urls.contains(&pref) {
+                    preferred_backend = Some(pref);
+                } else {
+                    println!("Warning: Provided preferred URL was not in the backend list. Ignoring preference.");
+                }
+            }
+        }
+
         let config = Config {
             listen_port,
             backend_urls,
+            preferred_backend,
         };
 
         let toml_content = toml::to_string_pretty(&config).expect("Failed to serialize config");
@@ -343,17 +373,23 @@ async fn main() {
     }
     let tray = LLMRouterTray {
         backend_data: initial_backend_data,
+        preferred_url: config.preferred_backend.clone(),
     };
     let tray_handle = tray.spawn().await.expect("Failed to start system tray");
 
     let state = AppState {
         backends: backends.clone(),
+        preferred_backend: config.preferred_backend.clone(),
         client: client.clone(),
         counter: Arc::new(AtomicUsize::new(0)),
     };
+
+    let tray_handle_clone = tray_handle.clone();
+    let pref_url_for_health = config.preferred_backend.clone();
     tokio::spawn(async move {
-        health_check_loop(backends, client, tray_handle).await;
+        health_check_loop(backends, pref_url_for_health, client, tray_handle_clone).await;
     });
+
     let app = Router::new()
         .route("/*path", any(proxy_handler))
         .fallback(any(proxy_handler))
@@ -370,6 +406,7 @@ async fn main() {
 
 async fn health_check_loop(
     backends: Vec<Backend>,
+    preferred_url: Option<String>,
     client: reqwest::Client,
     tray_handle: ksni::Handle<LLMRouterTray>,
 ) {
@@ -397,20 +434,33 @@ async fn health_check_loop(
             .iter()
             .map(|b| (b.url.clone(), b.healthy.load(Ordering::Relaxed)))
             .collect();
+        let pref_url_clone = preferred_url.clone();
         tray_handle
             .update(move |tray: &mut LLMRouterTray| {
                 tray.backend_data = snapshot;
+                tray.preferred_url = pref_url_clone;
             })
             .await;
         tokio::time::sleep(Duration::from_secs(5)).await;
     }
 }
 
-fn select_backend(backends: &[Backend], counter: &AtomicUsize) -> Option<String> {
+fn select_backend(
+    backends: &[Backend],
+    preferred_backend: &Option<String>,
+    counter: &AtomicUsize,
+) -> Option<String> {
     let len = backends.len();
     if len == 0 {
         return None;
     }
+    if let Some(pref) = preferred_backend {
+        if let Some(backend) = backends.iter().find(|b| &b.url == pref) {
+            if backend.healthy.load(Ordering::Relaxed) {
+                return Some(backend.url.clone());
+            }
+        }
+    }
     let start_idx = counter.fetch_add(1, Ordering::Relaxed);
     for i in 0..len {
         let idx = (start_idx + i) % len;
@@ -422,7 +472,8 @@ fn select_backend(backends: &[Backend], counter: &AtomicUsize) -> Option<String>
 }
 
 async fn proxy_handler(State(state): State<AppState>, req: Request<Body>) -> Response {
-    let backend_url = match select_backend(&state.backends, &state.counter) {
+    let backend_url =
+        match select_backend(&state.backends, &state.preferred_backend, &state.counter) {
             Some(url) => url,
             None => {
                 return (