Feat: Auto-resolve backend API base URL so Swarm redeploys no longer break proxied requests (fetch failed)

src/app/api/[...route]/route.ts

@@ -1,4 +1,5 @@
 import { NextRequest, NextResponse } from 'next/server';
+import { getApiBase, resetApiBase } from '@/lib/api-base';
 
 export async function GET(req: NextRequest, props: { params: Promise<{ route: string[] }> }) {
   return handleProxy(req, props);
@@ -27,9 +28,10 @@ async function handleProxy(req: NextRequest, { params }: { params: Promise<{ rou
     
     const url = new URL(req.url);
     
-    // INTERNAL_API_URL is read at RUNTIME (not baked at build time like NEXT_PUBLIC_*)
-    // This allows Docker Swarm / Portainer to set the backend URL dynamically
-    const localBase = process.env.INTERNAL_API_URL || process.env.NEXT_PUBLIC_API_URL || 'http://127.0.0.1:3001';
+    // INTERNAL_API_URL is read at RUNTIME (not baked at build time like NEXT_PUBLIC_*).
+    // getApiBase() probes configured URLs and transparently falls back to the stable
+    // Swarm service alias if the configured one (e.g. task hostname ...-0) is unreachable.
+    const localBase = await getApiBase();
     const destinationUrl = `${localBase}/api/${route}${url.search}`;
     
     // Prepare headers
@@ -67,7 +69,7 @@ async function handleProxy(req: NextRequest, { params }: { params: Promise<{ rou
       headers,
       body: body,
       cache: 'no-store', // Prevent Next.js from aggressively caching the backend response
-      // @ts-ignore
+      // @ts-expect-error - `duplex` is required for streaming bodies in older fetch typings
       duplex: hasBody ? 'half' : undefined,
     });
     
@@ -93,8 +95,11 @@ async function handleProxy(req: NextRequest, { params }: { params: Promise<{ rou
     }
 
     return nextResponse;
-  } catch (error: any) {
+  } catch (error) {
+    // Backend may have been redeployed (task hostname changed) — re-resolve next request.
+    resetApiBase();
     console.error('[Proxy Error]', error);
-    return NextResponse.json({ ok: false, message: error.message }, { status: 500 });
+    const message = error instanceof Error ? error.message : 'Unknown proxy error';
+    return NextResponse.json({ ok: false, message }, { status: 500 });
   }
 }

src/lib/api-base.ts

@@ -0,0 +1,75 @@
+// src/lib/api-base.ts
+// Server-only helper: resolve the backend API base URL at runtime.
+//
+// Why:
+//   The frontend proxies /api/* to the backend via NEXT_PUBLIC_API_URL /
+//   INTERNAL_API_URL. In Docker Swarm deployments these may point to a
+//   task-instance hostname like `backone-inspect-backend-bun-0:3001`. When the
+//   Swarm service is redeployed the task index can change (`-0` -> `-1`), orphaning
+//   the configured URL and breaking every proxied request ("fetch failed").
+//
+// Solution:
+//   Probe candidates in order and cache the first healthy one. Also auto-derive
+//   the stable service alias by stripping a trailing `-<digits>` suffix, so a
+//   stale `-0` URL transparently recovers to the plain service DNS name.
+
+let cachedBase: string | null = null;
+
+function pushUnique(list: string[], value?: string | null) {
+  if (!value) return;
+  const clean = value.replace(/\/+$/, '');
+  if (clean && !list.includes(clean)) list.push(clean);
+}
+
+function buildCandidates(): string[] {
+  const list: string[] = [];
+  pushUnique(list, process.env.INTERNAL_API_URL);
+  pushUnique(list, process.env.NEXT_PUBLIC_API_URL);
+
+  // Derive stable Swarm service alias (strip task index: ...-0 -> ...)
+  for (const base of [...list]) {
+    try {
+      const u = new URL(base);
+      const strippedHost = u.host.replace(/-\d+$/, '');
+      if (strippedHost && strippedHost !== u.host) {
+        pushUnique(list, `${u.protocol}//${strippedHost}`);
+      }
+    } catch {
+      // ignore malformed URLs
+    }
+  }
+
+  pushUnique(list, 'http://127.0.0.1:3001');
+  return list;
+}
+
+async function isHealthy(base: string): Promise<boolean> {
+  try {
+    const ctrl = new AbortController();
+    const timer = setTimeout(() => ctrl.abort(), 2500);
+    const res = await fetch(`${base}/api/health`, { signal: ctrl.signal });
+    clearTimeout(timer);
+    return res.ok;
+  } catch {
+    return false;
+  }
+}
+
+export async function getApiBase(): Promise<string> {
+  if (cachedBase) return cachedBase;
+
+  for (const base of buildCandidates()) {
+    if (await isHealthy(base)) {
+      cachedBase = base;
+      return base;
+    }
+  }
+
+  // Fallback: use the first configured candidate even if the probe failed.
+  cachedBase = buildCandidates()[0] || 'http://127.0.0.1:3001';
+  return cachedBase;
+}
+
+export function resetApiBase() {
+  cachedBase = null;
+}