CA-395174: Try to unarchive VM's metrics when they aren't running

Backport 71c3960

Non-running VMs' metrics are stored in the coordinator. When the coordinator is
asked about the metrics try to unarchive them instead of failing while trying
to fetch the coordinator's IP address.

This needs to force the HTTP method of the query to be POST

Also returns a Service Unavailable when the host is marked as Broken.

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

ocaml/xapi/rrdd_proxy.ml

@@ -77,17 +77,19 @@ let get_vm_rrd_forwarder (req : Http.Request.t) (s : Unix.file_descr) _ =
           Http_svr.headers s (Http.http_302_redirect url)
         in
         let unarchive () =
-          let req = {req with uri= Constants.rrd_unarchive_uri} in
+          let req = {req with m= Post; uri= Constants.rrd_unarchive_uri} in
           ignore
             (Xapi_services.hand_over_connection req s
                !Rrd_interface.forwarded_path
             )
         in
+        let unavailable () =
+          Http_svr.headers s (Http.http_503_service_unavailable ())
+        in
         (* List of conditions involved. *)
         let is_unarchive_request =
           List.mem_assoc Constants.rrd_unarchive query
         in
-        let is_master = Pool_role.is_master () in
         let is_owner_online owner = Db.is_valid_ref __context owner in
         let is_xapi_initialising = List.mem_assoc "dbsync" query in
         (* The logic. *)
@@ -99,15 +101,25 @@ let get_vm_rrd_forwarder (req : Http.Request.t) (s : Unix.file_descr) _ =
           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
-          if is_owner_localhost then
-            if is_master then
+          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. *)
               unarchive ()
-            else
+          | Slave _, true, _ | Slave _, _, false ->
+              (* Coordinator knows best *)
               unarchive_at_master ()
-          else if is_owner_online owner && not is_xapi_initialising then
-            read_at_owner owner
-          else
-            unarchive_at_master ()
+          | Broken, _, _ ->
+              info "%s: host is broken, VM's metrics are not available"
+                __FUNCTION__ ;
+              unavailable ()
     )
 
 (* Forward the request for host RRD data to the RRDD HTTP handler. If the host