To ensure the current repmgrd logfile (specified in repmgr.conf with the parameter log_file) does not grow indefinitely, configure your system's logrotate to regularly rotate it.

Sample configuration to rotate logfiles weekly with retention for up to 52 weeks and rotation forced if a file grows beyond 100Mb:

    /var/log/repmgr/repmgrd.log {
        missingok
        compress
        rotate 52
        maxsize 100M
        weekly
        create 0600 postgres postgres
        postrotate
            /usr/bin/killall -HUP repmgrd
        endscript
    }