Create new set of LB hosts on worker boot

As Rails 6.1 has automatic discard for all AR connection pools, we
need to create new connection pools.

https://gitlab.com/gitlab-org/gitlab/-/issues/332913

config/initializers/load_balancing.rb

@@ -11,6 +11,9 @@
 
   # This needs to be executed after fork of clustered processes
   Gitlab::Cluster::LifecycleEvents.on_worker_start do
+    # For Host-based LB, we need to re-connect as Rails discards connections on fork
+    Gitlab::Database::LoadBalancing.configure_proxy
+
     # Service discovery must be started after configuring the proxy, as service
     # discovery depends on this.
     Gitlab::Database::LoadBalancing.start_service_discovery