rabbit_khepri: Send a command instead of query for awaiting leadership

Author: the-mikedavis

deps/rabbit/src/rabbit_khepri.erl

@@ -294,10 +294,15 @@ wait_for_leader(_Timeout, 0) ->
 wait_for_leader(Timeout, Retries) ->
     rabbit_log:info("Waiting for Khepri leader for ~tp ms, ~tp retries left",
                     [Timeout, Retries - 1]),
-    Options = #{timeout => Timeout,
-                favor => low_latency},
-    case khepri:exists(?STORE_ID, [], Options) of
-        Exists when is_boolean(Exists) ->
+    %% We use a command (delete) rather than a query to check that a leader
+    %% has been elected. Khepri defaults to running queries against the local
+    %% member and local queries do not require an elected leader. In order to
+    %% apply a command though, the cluster must have a leader. So to await
+    %% leadership we send a command that should no-op: a delete of some node
+    %% that we will never use.
+    Options = ?DEFAULT_COMMAND_OPTIONS#{timeout => Timeout},
+    case khepri:delete(?STORE_ID, [does_not_exist], Options) of
+        ok ->
             rabbit_log:info("Khepri leader elected"),
             ok;
         {error, timeout} -> %% Khepri >= 0.14.0