From 5cf8a0854050fad259de5c775cda9e62e35853b6 Mon Sep 17 00:00:00 2001
From: MHSanaei <ho3ein.sanaei@gmail.com>
Date: Fri, 15 May 2026 11:24:50 +0200
Subject: [PATCH] fix: disable balancer fallbackTag for random / roundRobin
 strategies

Xray-core's RandomStrategy and RoundRobinStrategy register a pending
dependency on the Observatory feature whenever fallbackTag is non-empty.
Since the panel only provisions observatory for leastPing / leastLoad
balancers, picking roundRobin with a fallbackTag caused xray to fail
boot with "not all dependencies are resolved". Disable the fallback
field for the two strategies that cannot resolve it, and strip
fallbackTag from the wire balancer as a defensive backstop for users
who edit the JSON template directly.
---
 frontend/src/pages/xray/BalancerFormModal.vue | 15 +++++++++++++--
 frontend/src/pages/xray/BalancersTab.vue      |  3 ++-
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/frontend/src/pages/xray/BalancerFormModal.vue b/frontend/src/pages/xray/BalancerFormModal.vue
index 47dd2d41..05aabfeb 100644
--- a/frontend/src/pages/xray/BalancerFormModal.vue
+++ b/frontend/src/pages/xray/BalancerFormModal.vue
@@ -61,6 +61,16 @@ const isValid = computed(
   () => !tagEmpty.value && !duplicateTag.value && !emptySelector.value,
 );
 
+const fallbackSupported = computed(
+  () => form.strategy === 'leastPing' || form.strategy === 'leastLoad',
+);
+
+watch(() => form.strategy, (next) => {
+  if (next !== 'leastPing' && next !== 'leastLoad') {
+    form.fallbackTag = '';
+  }
+});
+
 const tagValidateStatus = computed(() => {
   if (tagEmpty.value) return 'error';
   if (duplicateTag.value) return 'warning';
@@ -111,8 +121,9 @@ const okText = computed(() =>
         </a-select>
       </a-form-item>
 
-      <a-form-item label="Fallback">
-        <a-select v-model:value="form.fallbackTag" allow-clear>
+      <a-form-item label="Fallback"
+        :help="fallbackSupported ? '' : 'Available only with Least ping / Least load'">
+        <a-select v-model:value="form.fallbackTag" allow-clear :disabled="!fallbackSupported">
           <a-select-option v-for="tag in ['', ...outboundTags]" :key="tag || '__empty'" :value="tag">
             {{ tag || `(${t('none')})` }}
           </a-select-option>
diff --git a/frontend/src/pages/xray/BalancersTab.vue b/frontend/src/pages/xray/BalancersTab.vue
index 0cf5b602..255ed108 100644
--- a/frontend/src/pages/xray/BalancersTab.vue
+++ b/frontend/src/pages/xray/BalancersTab.vue
@@ -145,10 +145,11 @@ function syncObservatories() {
 }
 
 function buildWireBalancer(form) {
+  const supportsFallback = form.strategy === 'leastPing' || form.strategy === 'leastLoad';
   const out = {
     tag: form.tag,
     selector: [...form.selector],
-    fallbackTag: form.fallbackTag,
+    fallbackTag: supportsFallback ? form.fallbackTag : '',
   };
   if (form.strategy && form.strategy !== 'random') {
     out.strategy = { type: form.strategy };