After several successful attempts using the exact same configuration and steps mentioned in early question here or here (with better preview)

I get stuck with no usable master

The master side

Jan 12 07:35:12 knot-master-1.novalocal knotd[12007]: info: [namadomain14.com.] zone file updated, serial 2018070410
Jan 12 07:35:12 knot-master-1.novalocal knotd[12007]: warning: [namadomain14.com.] notify, outgoing, remote slaveip@53, s...TAUTH'
Jan 12 07:37:18 knot-master-1.novalocal knotd[12007]: info: [namadomain14.com.] control, received command 'zone-begin'
Jan 12 07:37:32 knot-master-1.novalocal knotd[12007]: info: [namadomain14.com.] control, received command 'zone-set'
Jan 12 07:37:37 knot-master-1.novalocal knotd[12007]: info: [namadomain14.com.] control, received command 'zone-commit'
Jan 12 07:37:37 knot-master-1.novalocal knotd[12007]: info: [namadomain14.com.] zone file updated, serial 2018070410 -> 2018070412
Jan 12 07:37:37 knot-master-1.novalocal knotd[12007]: warning: [namadomain14.com.] notify, outgoing, remote slaveip@53, s...TAUTH'
Jan 12 07:37:41 knot-master-1.novalocal knotd[12007]: info: control, received command 'zone-read'
Jan 12 07:38:11 knot-master-1.novalocal knotd[12007]: info: [namadomain14.com.] control, received command 'zone-notify'
Jan 12 07:38:11 knot-master-1.novalocal knotd[12007]: warning: [namadomain14.com.] notify, outgoing, remote slaveip@53, s...TAUTH'

The slave side

Jan 12 07:34:54 knot-slave-1 knotd: info: control, received command 'conf-read'
Jan 12 07:35:19 knot-slave-1 systemd-logind: Removed session 2.
Jan 12 07:35:20 knot-slave-1 knotd: info: control, received command 'conf-begin'
Jan 12 07:35:20 knot-slave-1 knotd: notice: control, persistent configuration database not available
Jan 12 07:35:20 knot-slave-1 knotd: info: control, received command 'conf-set'
Jan 12 07:35:20 knot-slave-1 knotd: info: control, received command 'conf-set'
Jan 12 07:35:20 knot-slave-1 knotd: info: control, received command 'conf-set'
Jan 12 07:35:20 knot-slave-1 knotd: info: control, received command 'conf-commit'
Jan 12 07:35:20 knot-slave-1 knotd: info: [namadomain14.com.] zone will be loaded
Jan 12 07:35:20 knot-slave-1 knotd: info: [namadomain14.com.] failed to parse zone file (not exists)
Jan 12 07:35:21 knot-slave-1 knotd: warning: [namadomain14.com.] refresh, remote master1 not usable
Jan 12 07:35:21 knot-slave-1 knotd: error: [namadomain14.com.] refresh, failed (no usable master)
Jan 12 07:35:23 knot-slave-1 knotd: warning: [namadomain14.com.] refresh, remote master1 not usable
Jan 12 07:35:23 knot-slave-1 knotd: error: [namadomain14.com.] refresh, failed (no usable master)
Jan 12 07:35:27 knot-slave-1 knotd: info: control, received command 'zone-read'
Jan 12 07:35:29 knot-slave-1 knotd: info: control, received command 'zone-read'
Jan 12 07:35:34 knot-slave-1 knotd: warning: [namadomain14.com.] refresh, remote master1 not usable
Jan 12 07:35:34 knot-slave-1 knotd: error: [namadomain14.com.] refresh, failed (no usable master)
Jan 12 07:36:31 knot-slave-1 knotd: warning: [namadomain14.com.] refresh, remote master1 not usable
Jan 12 07:36:31 knot-slave-1 knotd: error: [namadomain14.com.] refresh, failed (no usable master)
Jan 12 07:37:14 knot-slave-1 knotd: info: [namadomain14.com.] control, received command 'zone-begin'
Jan 12 07:37:55 knot-slave-1 knotd: info: [namadomain14.com.] control, received command 'zone-abort'
Jan 12 07:38:19 knot-slave-1 knotd: info: control, received command 'zone-read'
Jan 12 07:39:12 knot-slave-1 knotd: warning: [namadomain14.com.] refresh, remote master1 not usable
Jan 12 07:39:12 knot-slave-1 knotd: error: [namadomain14.com.] refresh, failed (no usable master)

Problems

Previously, even though I have ‘NO AUTH’ in master side. The zone in slave still crated, because I don’t get no usable master.
But the sudden there is no usable master. I’ve tried:

• sudo service knot restart
• remove everything -> reinstall everything

Both give me no luck.

Thank you in advance.