Update app.py

app.py

@@ -4,7 +4,12 @@ import streamlit.components.v1 as components
 
 st.set_page_config(layout="wide")
 
-backend_url = os.getenv("backend", "https://www.bytedance.com/en/")  # 如果环境变量不存在，则使用默认 URL
+# List of backend URLs
+backends = ["backend1", "backend2", "backend3", "backend4"]
+
+# Randomly select a backend URL
+backend = random.choice(backends)
+backend_url = os.getenv(backend, "https://www.bytedance.com/en/")  # 如果环境变量不存在，则使用默认 URL
 
 iframe_html = f'<iframe src="{backend_url}" width="100%" height="800"></iframe>'