Fix empty DLQ replay; add chaos status banner to UI

whummer · claude · whummer · commit ef12588a4ce8 · 2026-04-18T16:56:02.000+02:00
- replay_dlq.py: handle empty stdout from receive-message (empty DLQ)
- index.html: poll /_localstack/chaos/faults every 5s, show warning
  banner with active fault details when chaos mode is enabled

Co-Authored-By: Claude Sonnet 4.6 &lt;noreply@anthropic.com&gt;
diff --git a/01-serverless-app/website/index.html b/01-serverless-app/website/index.html
@@ -145,6 +145,20 @@
 
     #api-bar { font-size: 0.78rem; color: #aaa; margin-bottom: 1rem; }
     #api-bar code { background: #f0f0f0; padding: 0.1rem 0.4rem; border-radius: 4px; }
+
+    #chaos-banner {
+      display: none;
+      background: #fff3cd;
+      border: 1px solid #ffc107;
+      border-radius: 8px;
+      padding: 0.75rem 1rem;
+      margin-bottom: 1.5rem;
+      font-size: 0.875rem;
+      color: #856404;
+    }
+    #chaos-banner.active { display: block; }
+    #chaos-banner strong { font-weight: 700; }
+    #chaos-faults { font-family: monospace; font-size: 0.8rem; margin-top: 0.4rem; white-space: pre-wrap; }
   </style>
 </head>
 <body>
@@ -157,6 +171,11 @@ <h1>Order Processing Pipeline</h1>
 <main>
   <p id="api-bar">API endpoint: <code id="api-url"></code></p>
 
+  <div id="chaos-banner">
+    <strong>⚠ Chaos mode active</strong> — fault injections are enabled, orders may fail or get stuck.
+    <div id="chaos-faults"></div>
+  </div>
+
   <div class="card">
     <h2>New Order</h2>
     <form id="order-form">
@@ -340,6 +359,22 @@ <h2>Orders</h2>
     return String(s).replace(/[&<>"']/g, c => ({"&":"&amp;","<":"&lt;",">":"&gt;",'"':"&quot;","'":"&#39;"}[c]));
   }
 
+  async function checkChaos() {
+    try {
+      const res = await fetch(`${window.location.origin}/_localstack/chaos/faults`);
+      const faults = await res.json();
+      const banner = document.getElementById("chaos-banner");
+      if (Array.isArray(faults) && faults.length > 0) {
+        banner.classList.add("active");
+        document.getElementById("chaos-faults").textContent = JSON.stringify(faults, null, 2);
+      } else {
+        banner.classList.remove("active");
+      }
+    } catch (e) { /* LocalStack not reachable, ignore */ }
+  }
+
+  checkChaos();
+  setInterval(checkChaos, 5000);
   loadOrders();
 </script>
 </body>
diff --git a/04-chaos-engineering/scripts/replay_dlq.py b/04-chaos-engineering/scripts/replay_dlq.py
@@ -15,7 +15,12 @@
     aws_secret_access_key="test",
 )
 
-data = json.load(sys.stdin)
+raw = sys.stdin.read().strip()
+if not raw:
+    print("DLQ is empty.")
+    sys.exit(0)
+
+data = json.loads(raw)
 messages = data.get("Messages", [])
 
 if not messages:
