PLAY [nfs_servers] ERROR about acs-jupyterhub HOT 1 OPEN

Note that i tried to reproduce the error by connecting manually to the master and then running the following command:

datahub@k8s-master-30868763-0:~$ sudo bash bootstrap/setup.bash k8s-es5-3
gpg: keyring /tmp/tmpvqce26ad/secring.gpg' created gpg: keyring /tmp/tmpvqce26ad/pubring.gpg' created
gpg: requesting key 7BB9C367 from hkp server keyserver.ubuntu.com
gpg: /tmp/tmpvqce26ad/trustdb.gpg: trustdb created
gpg: key 7BB9C367: public key "Launchpad PPA for Ansible, Inc." imported
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)

PLAY [nfs_servers] ***************************************************************************************************************

TASK [Gathering Facts] ***********************************************************************************************************
The authenticity of host 'nfsserver (10.240.0.7)' can't be established.
ECDSA key fingerprint is SHA256:DV0o72nVqF1v5P3QSQgapbf2anEXxFt2kDZOr8pPr6c.
Are you sure you want to continue connecting (yes/no)? yes
ok: [nfsserver]

TASK [install zfsutils-linux] ****************************************************************************************************
ok: [nfsserver]

TASK [install nfs server packages] ***********************************************************************************************
changed: [nfsserver]

TASK [add mount path to /etc/exports] ********************************************************************************************
changed: [nfsserver]

TASK [create zfs filesystem] *****************************************************************************************************
changed: [nfsserver]

TASK [gather zfs facts] **********************************************************************************************************
ok: [nfsserver]

TASK [check if zfs dataset is mounted] *******************************************************************************************
skipping: [nfsserver] => (item={u'setuid': u'on', u'relatime': u'off', u'referenced': u'96K', u'logicalused': u'40K', u'zoned': u'off', u'primarycache': u'all', u'logbias': u'latency', u'creation': u'Mon Aug 28 14:32 2017', u'sync': u'standard', u'snapdev': u'hidden', u'dedup': u'off', u'sharenfs': u'off', u'acltype': u'off', u'sharesmb': u'off', u'canmount': u'on', u'mountpoint': u'/export/pool0/homes', u'casesensitivity': u'sensitive', u'utf8only': u'off', u'usedbysnapshots': u'0', u'defcontext': u'none', u'rootcontext': u'none', u'mounted': u'yes', u'compression': u'off', u'snapdir': u'hidden', u'overlay': u'off', u'xattr': u'on', u'exec': u'on', u'copies': u'1', u'snapshot_limit': u'none', u'aclinherit': u'restricted', u'compressratio': u'1.00x', u'readonly': u'off', u'version': u'5', u'recordsize': u'128K', u'filesystem_limit': u'none', u'type': u'filesystem', u'secondarycache': u'all', u'refreservation': u'none', u'available': u'129G', u'used': u'96K', u'written': u'96K', u'refquota': u'none', u'refcompressratio': u'1.00x', u'quota': u'none', u'snapshot_count': u'none', u'fscontext': u'none', u'vscan': u'off', u'reservation': u'none', u'usedbyrefreservation': u'0', u'atime': u'on', u'normalization': u'none', u'usedbychildren': u'0', u'usedbydataset': u'96K', u'name': u'pool0/homes', u'mlslabel': u'none', u'redundant_metadata': u'all', u'filesystem_count': u'none', u'devices': u'on', u'logicalreferenced': u'40K', u'context': u'none', u'checksum': u'on', u'nbmand': u'off'})

TASK [create mount path directory] ***********************************************************************************************
ok: [nfsserver]

TASK [set permissions on /export] ************************************************************************************************
changed: [nfsserver]

TASK [export filesystem] *********************************************************************************************************
changed: [nfsserver]

PLAY [nfs_clients] ***************************************************************************************************************

TASK [Gathering Facts] ***********************************************************************************************************
The authenticity of host 'k8s-master-30868763-0 (10.240.255.5)' can't be established.
ECDSA key fingerprint is SHA256:ZGQYbw8c+2HaVXZkEGjPnA/ZqWHo3F/GL8wv5wh9LtE.
Are you sure you want to continue connecting (yes/no)? The authenticity of host 'k8s-master-30868763-1 (10.240.255.6)' can't be established.
ECDSA key fingerprint is SHA256:hgfFKYPerkyRG6qGTdMZVjnQMyHF+ZmLXqGpVYkI8oU.
Are you sure you want to continue connecting (yes/no)? The authenticity of host 'k8s-pool1-30868763-1 (10.240.0.5)' can't be established.
ECDSA key fingerprint is SHA256:J38QSk0kk6OqTwP5NzoGVl19UPfpoX+sL4mTI2ftdbc.
Are you sure you want to continue connecting (yes/no)? The authenticity of host 'k8s-master-30868763-2 (10.240.255.7)' can't be established.
ECDSA key fingerprint is SHA256:aU7srVuxtqPUxk7otYMFVX1LkUm6SGbWAkjYXuw4JmQ.
Are you sure you want to continue connecting (yes/no)? The authenticity of host 'k8s-pool1-30868763-0 (10.240.0.6)' can't be established.
ECDSA key fingerprint is SHA256:17NISRiYtleUuGeSI4mNcIXxJ5xWzOo3ZGT93gFRTJc.
Are you sure you want to continue connecting (yes/no)? yes
ok: [k8s-master-30868763-0]
The authenticity of host 'k8s-pool1-30868763-2 (10.240.0.4)' can't be established.
ECDSA key fingerprint is SHA256:JnxYbHUNQC85b2hCIhNTIbg4fJAZtwtNtc4LleOrQbY.
Are you sure you want to continue connecting (yes/no)? yes
ok: [k8s-master-30868763-1]

fatal: [k8s-pool1-30868763-1]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Host key verification failed.\r\n", "unreachable": true}

fatal: [k8s-master-30868763-2]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Host key verification failed.\r\n", "unreachable": true}

fatal: [k8s-pool1-30868763-0]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Host key verification failed.\r\n", "unreachable": true}

fatal: [k8s-pool1-30868763-2]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Host key verification failed.\r\n", "unreachable": true}

TASK [install nfs client packages] ***********************************************************************************************

changed: [k8s-master-30868763-0]
changed: [k8s-master-30868763-1]

TASK [create mount path] *********************************************************************************************************
changed: [k8s-master-30868763-1]
changed: [k8s-master-30868763-0]

TASK [mount nfs filesystem] ******************************************************************************************************
changed: [k8s-master-30868763-0]
changed: [k8s-master-30868763-1]

TASK [make /data] ****************************************************************************************************************
changed: [k8s-master-30868763-0]
changed: [k8s-master-30868763-1]

TASK [make symlink to /data/homes] ***********************************************************************************************
changed: [k8s-master-30868763-0]
changed: [k8s-master-30868763-1]
to retry, use: --limit @/home/datahub/k8s-nfs-ansible/playbook.retry

PLAY RECAP ***********************************************************************************************************************
k8s-master-30868763-0 : ok=6 changed=5 unreachable=0 failed=0
k8s-master-30868763-1 : ok=6 changed=5 unreachable=0 failed=0
k8s-master-30868763-2 : ok=0 changed=0 unreachable=1 failed=0
k8s-pool1-30868763-0 : ok=0 changed=0 unreachable=1 failed=0
k8s-pool1-30868763-1 : ok=0 changed=0 unreachable=1 failed=0
k8s-pool1-30868763-2 : ok=0 changed=0 unreachable=1 failed=0
nfsserver : ok=9 changed=5 unreachable=0 failed=0

from acs-jupyterhub.