fix upstream does not contain a target when init

apps/api/src/services/nginx/info/upstream.rs

@@ -54,13 +54,13 @@ impl NginxConfigProvider for UpstreamInfo {
             .iter()
             .map(|target| target.to_nginx_config(Some(indent.unwrap_or(0) + INDENT_SIZE)))
             .collect();
-
-        format!(
-            "upstream {} {{\n{}\n}}",
-            self.name,
-            targets_config.join("\n".indent(indent.unwrap_or(0) + INDENT_SIZE).as_str())
-        )
-        .indent(indent.unwrap_or(0))
+        let targets_config_str = if targets_config.is_empty() {
+            "server 127.0.0.1:65535 down; # placeholder target".to_string()
+        } else {
+            targets_config.join("\n")
+        }
+        .indent(indent.unwrap_or(0) + INDENT_SIZE);
+        format!("upstream {} {{\n{}\n}}", self.name, targets_config_str).indent(indent.unwrap_or(0))
     }
 }