Handle inability to contact metrics server on forwarding

src/lib/mina_metrics/prometheus_metrics/dune

@@ -18,11 +18,12 @@
    base.base_internalhash_types
    uri
    async_unix
+   base.caml
    ;; local libraries
    logger
    o1trace
  )
  (preprocessor_deps ../../../config.mlh)
  (instrumentation (backend bisect_ppx))
- (preprocess (pps ppx_mina ppx_let ppx_version ppx_pipebang ppx_custom_printf ppx_optcomp))
+ (preprocess (pps ppx_mina ppx_let ppx_version ppx_pipebang ppx_custom_printf ppx_optcomp ppx_here))
  (implements mina_metrics))

src/lib/mina_metrics/prometheus_metrics/mina_metrics.ml

@@ -1665,20 +1665,33 @@ let generic_server ?forward_uri ~port ~logger ~registry () =
     | `GET, "/metrics" ->
         let%bind other_data =
           match forward_uri with
-          | Some uri ->
-              let%bind resp, body = Client.get uri in
-              let status = Response.status resp in
-              if Code.is_success (Code.code_of_status status) then
-                let%map body = Body.to_string body in
-                Some body
-              else (
-                [%log error] "Could not forward request to $url, got: $status"
-                  ~metadata:
-                    [ ("url", `String (Uri.to_string uri))
-                    ; ("status_code", `Int (Code.code_of_status status))
-                    ; ("status", `String (Code.string_of_status status))
-                    ] ;
-                return None )
+          | Some uri -> (
+              Monitor.try_with ~here:[%here] (fun () ->
+                  let%bind resp, body = Client.get uri in
+                  let status = Response.status resp in
+                  if Code.is_success (Code.code_of_status status) then
+                    let%map body = Body.to_string body in
+                    Some body
+                  else (
+                    [%log error]
+                      "Could not forward request to $url, got: $status"
+                      ~metadata:
+                        [ ("url", `String (Uri.to_string uri))
+                        ; ("status_code", `Int (Code.code_of_status status))
+                        ; ("status", `String (Code.string_of_status status))
+                        ] ;
+                    return None ) )
+              >>| function
+              | Ok a ->
+                  a
+              | Error e ->
+                  [%log error]
+                    "Could not forward request to $url, got error: $error"
+                    ~metadata:
+                      [ ("url", `String (Uri.to_string uri))
+                      ; ("error", `String (Exn.to_string_mach e))
+                      ] ;
+                  None )
           | None ->
               return None
         in