repmgrd: ensure cascaded standby reconnects to primary

If the primary connection went away, and the upstream is not the
primary, attempt to reconnect if the monitoring update fails.

If the upstream is the primary, the reconnection will happen on
the next connection check.

repmgrd-physical.c

@@ -109,7 +109,7 @@ static bool do_primary_failover(void);
 static bool do_upstream_standby_failover(void);
 static bool do_witness_failover(void);
 
-static void update_monitoring_history(void);
+static bool update_monitoring_history(void);
 
 static void handle_sighup(PGconn **conn, t_server_type server_type);
 
@@ -1984,7 +1984,17 @@ loop:
 
 		if (PQstatus(primary_conn) == CONNECTION_OK && config_file_options.monitoring_history == true)
 		{
-			update_monitoring_history();
+			bool success = update_monitoring_history();
+
+			if (success == false && PQstatus(primary_conn) != CONNECTION_OK && upstream_node_info.type == STANDBY)
+			{
+				primary_conn = establish_primary_db_connection(local_conn, false);
+
+				if (PQstatus(primary_conn) == CONNECTION_OK)
+				{
+					(void)update_monitoring_history();
+				}
+			}
 		}
 		else
 		{
@@ -3111,7 +3121,7 @@ do_primary_failover(void)
 }
 
 
-static void
+static bool
 update_monitoring_history(void)
 {
 	ReplInfo	replication_info;
@@ -3124,13 +3134,13 @@ update_monitoring_history(void)
 	if (PQstatus(primary_conn) != CONNECTION_OK)
 	{
 		log_warning(_("primary connection is not available, unable to update monitoring history"));
-		return;
+		return false;
 	}
 
 	if (PQstatus(local_conn) != CONNECTION_OK)
 	{
 		log_warning(_("local connection is not available, unable to update monitoring history"));
-		return;
+		return false;
 	}
 
 	init_replication_info(&replication_info);
@@ -3138,7 +3148,7 @@ update_monitoring_history(void)
 	if (get_replication_info(local_conn, STANDBY, &replication_info) == false)
 	{
 		log_warning(_("unable to retrieve replication status information, unable to update monitoring history"));
-		return;
+		return false;
 	}
 
 	/*
@@ -3157,7 +3167,7 @@ update_monitoring_history(void)
 	if (primary_last_wal_location == InvalidXLogRecPtr)
 	{
 		log_warning(_("unable to retrieve primary's current LSN"));
-		return;
+		return false;
 	}
 
 	/* calculate apply lag in bytes */
@@ -3201,6 +3211,8 @@ update_monitoring_history(void)
 						  apply_lag_bytes);
 
 	INSTR_TIME_SET_CURRENT(last_monitoring_update);
+
+	return true;
 }