fix(CubeProxy): initialize random seed in worker phase (#138)

In OpenResty, all worker processes inherit the same state from the
master process. Without explicitly seeding the random number generator
in the init_worker phase, each worker starts with the same default
seed. This results in math.random() producing the exact same sequence
of numbers across all workers.

Seeding with (ngx.now() * 1000 + ngx.worker.id()) ensures that each
worker has a unique, time-varying seed. This is essential for features
like cache TTL jitter to work as intended and avoid synchronized
cache expiration stampedes.

Signed-off-by: novahe <heqianfly@gmail.com>

Author: novahe

CubeProxy/lua/init_worker_phase.lua

@@ -1,3 +1,10 @@
+-- In OpenResty, math.randomseed should be called in the init_worker phase.
+-- Without this, all worker processes would start with the same seed (typically 1),
+-- causing math.random() to return the same sequence of values across all workers.
+-- This is critical for cache TTL jitter and other randomized behaviors to ensure
+-- they are truly distributed and don't lead to synchronized stampedes.
+math.randomseed(ngx.now() * 1000 + ngx.worker.id())
+
 local function monitor_cache_usage()
     local cache_free_space = ngx.shared.local_cache:free_space()
     ngx.shared.local_cache:set("cache_free_space", cache_free_space)