fix(clustering/rpc): dont start too many timers for sync (#14089)

KAG-6114

kong/clustering/services/sync/rpc.lua

@@ -369,7 +369,7 @@ local sync_once_impl
 
 
 local function start_sync_once_timer(retry_count)
-  local ok, err = ngx.timer.at(0, sync_once_impl, retry_count or 0)
+  local ok, err = kong.timer:at(0, sync_once_impl, retry_count or 0)
   if not ok then
     return nil, err
   end
@@ -385,6 +385,8 @@ function sync_once_impl(premature, retry_count)
 
   sync_handler()
 
+  -- check if "kong.sync.v2.notify_new_version" updates the latest version
+
   local latest_notified_version = ngx.shared.kong:get(CLUSTERING_DATA_PLANES_LATEST_VERSION_KEY)
   if not latest_notified_version then
     ngx_log(ngx_DEBUG, "no version notified yet")
@@ -409,7 +411,15 @@ end
 
 
 function _M:sync_once(delay)
-  return ngx.timer.at(delay or 0, sync_once_impl, 0)
+  local name = "rpc_sync_v2_once"
+  local is_managed = kong.timer:is_managed(name)
+
+  -- we are running a sync handler
+  if is_managed then
+    return true
+  end
+
+  return kong.timer:named_at(name, delay or 0, sync_once_impl, 0)
 end