CA-395174: rrdd_proxy: Use Option to encode where VMs might be availa…

…ble at

Backport 6bb7702

This makes the selection of the action obvious, previously the two booleans
made it hazy to understand the decision, and was part of the error why the
coordinator tried to get the coordinator address from the pool_role file (and
failed badly)

Signed-off-by: Pau Ruiz Safont <[email protected]>
Signed-off-by: Christian Lindig <[email protected]>

ocaml/xapi/rrdd_proxy.ml

@@ -51,6 +51,7 @@ let fail_req_with (s : Unix.file_descr) msg (http_err : unit -> string list) =
  *)
 let get_vm_rrd_forwarder (req : Http.Request.t) (s : Unix.file_descr) _ =
   debug "put_rrd_forwarder: start" ;
+  let __FUNCTION__ = "get_vm_rrd_forwarder" in
   let query = req.Http.Request.query in
   req.Http.Request.close <- true ;
   let vm_uuid = List.assoc "uuid" query in
@@ -65,8 +66,7 @@ let get_vm_rrd_forwarder (req : Http.Request.t) (s : Unix.file_descr) _ =
     Xapi_http.with_context ~dummy:true "Get VM RRD." req s (fun __context ->
         let open Http.Request in
         (* List of possible actions. *)
-        let read_at_owner owner =
-          let address = Db.Host.get_address ~__context ~self:owner in
+        let read_at address =
           let url = make_url ~address ~req in
           Http_svr.headers s (Http.http_302_redirect url)
         in
@@ -89,35 +89,40 @@ let get_vm_rrd_forwarder (req : Http.Request.t) (s : Unix.file_descr) _ =
         let is_unarchive_request =
           List.mem_assoc Constants.rrd_unarchive query
         in
-        let is_owner_online owner = Db.is_valid_ref __context owner in
-        let is_xapi_initialising = List.mem_assoc "dbsync" query in
+        let metrics_at () =
+          let ( let* ) = Option.bind in
+          let owner_of vm =
+            let owner = Db.VM.get_resident_on ~__context ~self:vm in
+            let is_xapi_initialising = List.mem_assoc "dbsync" query in
+            let is_available = not is_xapi_initialising in
+            if Db.is_valid_ref __context owner && is_available then
+              Some owner
+            else
+              None
+          in
+          let* owner = owner_of (Db.VM.get_by_uuid ~__context ~uuid:vm_uuid) in
+          let owner_uuid = Db.Host.get_uuid ~__context ~self:owner in
+          if owner_uuid = Helpers.get_localhost_uuid () then
+            (* VM is local but metrics aren't available *)
+            None
+          else
+            let address = Db.Host.get_address ~__context ~self:owner in
+            Some address
+        in
         (* The logic. *)
         if is_unarchive_request then
           unarchive ()
         else
-          let localhost_uuid = Helpers.get_localhost_uuid () in
-          let vm_ref = Db.VM.get_by_uuid ~__context ~uuid:vm_uuid in
-          let owner = Db.VM.get_resident_on ~__context ~self:vm_ref in
-          let owner_uuid = Ref.string_of owner in
-          let is_owner_localhost = owner_uuid = localhost_uuid in
-          let owner_is_available =
-            is_owner_online owner && not is_xapi_initialising
-          in
-          match
-            (Pool_role.get_role (), is_owner_localhost, owner_is_available)
-          with
-          | (Master | Slave _), false, true ->
-              (* VM is running elsewhere *)
-              read_at_owner owner
-          | Master, true, _ | Master, false, false ->
-              (* VM running on node, or not running at all. *)
+          match (Pool_role.get_role (), metrics_at ()) with
+          | (Master | Slave _), Some owner ->
+              read_at owner
+          | Master, None ->
               unarchive ()
-          | Slave coordinator, true, _ | Slave coordinator, _, false ->
-              (* Coordinator knows best *)
+          | Slave coordinator, None ->
               unarchive_at coordinator
-          | Broken, _, _ ->
+          | Broken, _ ->
               info "%s: host is broken, VM's metrics are not available"
-                "get_vm_rrd_forwarder" ;
+                __FUNCTION__ ;
               unavailable ()
     )