connection with the ha-availability software 'repmgr' broke down for idle

Firstly, I fixed the connection close issue by activating 'keep-alive' configuration on postgresql.conf:
tcp_keepalives_idle = 20                # TCP_KEEPIDLE, in seconds;
                                        # 0 selects the system default
tcp_keepalives_interval = 10            # TCP_KEEPINTVL, in seconds;
                                        # 0 selects the system default
tcp_keepalives_count = 3                # TCP_KEEPCNT;

It basically echo's ping-pong heartbeat with the client to avoid a router in between them considers the tcp connection as idle and automatically closes it.

But unfortunately I encountered the loss of connections between a repmgr with local postgresql (primary) server

2023-11-01 06:11:41+0800: repmgrd_local_disconnect on node2, unable to connect to local node - happened
2023-11-01 06:11:57.750148+08: repmgrd_local_reconnect on node2, reconnected to local node after 16 seconds - happened

They left no record in the log of postgresql

It does not matter what type of alive checking in repmgr.conf I set:
connection_check_type=ping|connection|query

I found that after long time, the connection between repmgr and postgresql would be labeled as 'idle' from htop of ps -ef