Fix nginx site monitoring to properly detect errors

- Return error status for HTTP 502/5xx responses instead of success
- Show 'error' description for sites with connectivity but wrong status codes
- Show 'unreachable' description for complete connection failures
- Each nginx site now has independent status based on actual health
- Sites with timeouts or server errors will trigger notifications

agent/src/collectors/service.rs

@@ -832,7 +832,8 @@ impl ServiceCollector {
         std::env::var("UID").unwrap_or_default() == "0"
     }
 
-    async fn measure_site_latency(&self, site_name: &str) -> Option<f32> {
+    async fn measure_site_latency(&self, site_name: &str) -> (Option<f32>, bool) {
+        // Returns (latency, is_healthy)
         // Construct URL from site name
         let url = if site_name.contains("localhost") || site_name.contains("127.0.0.1") {
             format!("http://{}", site_name)
@@ -841,10 +842,13 @@ impl ServiceCollector {
         };
         
         // Create HTTP client with short timeout
-        let client = reqwest::Client::builder()
+        let client = match reqwest::Client::builder()
             .timeout(Duration::from_secs(5))
             .build()
-            .ok()?;
+        {
+            Ok(client) => client,
+            Err(_) => return (None, false),
+        };
         
         let start = Instant::now();
         
@@ -852,16 +856,12 @@ impl ServiceCollector {
         match client.head(&url).send().await {
             Ok(response) => {
                 let latency = start.elapsed().as_millis() as f32;
-                if response.status().is_success() || response.status().is_redirection() {
-                    Some(latency)
-                } else {
-                    // Site is reachable but returned error, still measure latency
-                    Some(latency)
-                }
+                let is_healthy = response.status().is_success() || response.status().is_redirection();
+                (Some(latency), is_healthy)
             }
             Err(_) => {
-                // Connection failed, no latency measurement
-                None
+                // Connection failed, no latency measurement, not healthy
+                (None, false)
             }
         }
     }
@@ -1355,13 +1355,14 @@ impl Collector for ServiceCollector {
                         // Add nginx sites as individual sub-services
                         if let Some(sites) = self.get_nginx_sites().await {
                             for site in sites.iter() {
-                                // Measure latency for this site
-                                let latency = self.measure_site_latency(site).await;
+                                // Measure latency and health for this site
+                                let (latency, is_healthy) = self.measure_site_latency(site).await;
                                 
-                                // Determine status and description based on latency measurement
-                                let (site_status, site_description) = match latency {
-                                    Some(_ms) => (ServiceStatus::Running, None),
-                                    None => (ServiceStatus::Stopped, Some(vec!["unreachable".to_string()])),
+                                // Determine status and description based on latency and health
+                                let (site_status, site_description) = match (latency, is_healthy) {
+                                    (Some(_ms), true) => (ServiceStatus::Running, None),
+                                    (Some(_ms), false) => (ServiceStatus::Stopped, Some(vec!["error".to_string()])),
+                                    (None, _) => (ServiceStatus::Stopped, Some(vec!["unreachable".to_string()])),
                                 };
                                 
                                 // Update counters based on site status