Add Prometheus Service Discovery for online devices (#3788)

esphome/dashboard/dashboard.py

@@ -644,6 +644,33 @@ def _ping_func(filename, address):
     return filename, rc == 0
 
 
+class PrometheusServiceDiscoveryHandler(BaseHandler):
+    @authenticated
+    def get(self):
+        entries = _list_dashboard_entries()
+        self.set_header("content-type", "application/json")
+        sd = []
+        for entry in entries:
+            if entry.web_port is None:
+                continue
+            labels = {
+                "__meta_name": entry.name,
+                "__meta_esp_platform": entry.target_platform,
+                "__meta_esphome_version": entry.storage.esphome_version,
+            }
+            for integration in entry.storage.loaded_integrations:
+                labels[f"__meta_integration_{integration}"] = "true"
+            sd.append(
+                {
+                    "targets": [
+                        f"{entry.address}:{entry.web_port}",
+                    ],
+                    "labels": labels,
+                }
+            )
+        self.write(json.dumps(sd))
+
+
 class MDNSStatusThread(threading.Thread):
     def run(self):
         global IMPORT_RESULT
@@ -993,6 +1020,7 @@ def make_app(debug=get_bool_env(ENV_DEV)):
             (f"{rel}import", ImportRequestHandler),
             (f"{rel}secret_keys", SecretKeysRequestHandler),
             (f"{rel}rename", EsphomeRenameHandler),
+            (f"{rel}prometheus-sd", PrometheusServiceDiscoveryHandler),
         ],
         **app_settings,
     )