vmui: fix the display of the link to vmalert (#7380)

### Describe Your Changes

Fix the issue mentioned in
https://github.com/VictoriaMetrics/VictoriaMetrics/pull/7088#issuecomment-2391360368

### Checklist

The following checks are **mandatory**:

- [ ] My change adheres [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).

(cherry picked from commit bfb55d5f2f)

app/vmui/packages/vmui/src/hooks/useFetchFlags.ts

@@ -1,7 +1,6 @@
 import { useAppDispatch, useAppState } from "../state/common/StateContext";
 import { useEffect, useState } from "preact/compat";
 import { ErrorTypes } from "../types";
-import { getUrlWithoutTenant } from "../utils/tenants";
 
 const useFetchFlags = () => {
   const { serverUrl } = useAppState();
@@ -17,7 +16,7 @@ const useFetchFlags = () => {
       setIsLoading(true);
 
       try {
-        const url = getUrlWithoutTenant(serverUrl);
+        const url = new URL(serverUrl).origin;
         const response = await fetch(`${url}/flags`);
         const data = await response.text();
         const flags = data.split("\n").filter(flag => flag.trim() !== "")

app/vmui/packages/vmui/src/router/navigation.ts

@@ -1,4 +1,5 @@
 import router, { routerOptions } from "./index";
+import { getTenantIdFromUrl } from "../utils/tenants";
 
 export enum NavigationItemType {
   internalLink,
@@ -24,10 +25,12 @@ interface NavigationConfig {
  * Special case for alert link
  */
 const getAlertLink = (url: string, showAlertLink: boolean) => {
-  // see more https://docs.victoriametrics.com/cluster-victoriametrics/?highlight=vmalertproxyurl#vmalert
+  // see more https://docs.victoriametrics.com/cluster-victoriametrics/#vmalert
+  const isCluster = !!getTenantIdFromUrl(url);
+  const value = isCluster ? `${url}/vmalert` : url.replace(/\/prometheus$/, "/vmalert");
   return {
     label: "Alerts",
-    value: `${url}/vmalert`,
+    value,
     type: NavigationItemType.externalLink,
     hide: !showAlertLink,
   };

docs/changelog/CHANGELOG.md

@@ -28,6 +28,7 @@ See also [LTS releases](https://docs.victoriametrics.com/lts-releases/).
 * BUGFIX: [vmalert](https://docs.victoriametrics.com/vmalert): properly set `group_name` and `file` fields for recording rules in `/api/v1/rules`.
 * BUGFIX: [Single-node VictoriaMetrics](https://docs.victoriametrics.com/) and `vmstorage` in [VictoriaMetrics cluster](https://docs.victoriametrics.com/cluster-victoriametrics/): prevent panic when ingesting samples which are outisde of configured [retention filters](https://docs.victoriametrics.com/#retention-filters). This could happen when backfilling data with retention filters which exclude samples from the backfill range.
 * BUGFIX: [vmctl](https://docs.victoriametrics.com/vmctl/): fix issue with series matching for `vmctl vm-native` with `--vm-native-disable-per-metric-migration` flag enabled. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/7309).
+* BUGFIX: [vmui](https://docs.victoriametrics.com/#vmui): fix the display of the link to vmalert. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5924).
 
 ## [v1.105.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.105.0)