fix: improve least_conn balancer implementation

Author: coder2z

apisix/balancer/least_conn.lua

@@ -31,15 +31,14 @@ local _M = {}
 local CONN_COUNT_DICT_NAME = "balancer-least-conn"
 local conn_count_dict = ngx_shared[CONN_COUNT_DICT_NAME]
 
--- Initialize shared dictionary at module load time
-if not conn_count_dict then
+-- Check that the shared dictionary exists
+if ngx.shared and conn_count_dict == nil then
     core.log.error("shared dict '", CONN_COUNT_DICT_NAME, "' not found, ",
             "please add 'lua_shared_dict ", CONN_COUNT_DICT_NAME, " 10m;' ",
             "to your nginx configuration")
     error("shared dict '" .. CONN_COUNT_DICT_NAME .. "' not found")
 end
 
-
 local function least_score(a, b)
     return a.score < b.score
 end
@@ -132,6 +131,10 @@ end
 
 
 function _M.new(up_nodes, upstream)
+    if not conn_count_dict then
+        return nil, "dictionary not find"
+    end
+
     local servers_heap = binaryHeap.minUnique(least_score)
 
     -- Clean up stale connection counts for removed servers