Hello everyone, I was able to update successfully.

Here are the steps:

UPDATE OPENSTACK VERSION OCETA FOR PIKE UBUNTU

UPDATE OF THE CONTROLLER Node

1) PAUSE ALL SERVICES service glance-registry stop service glance-api stop service nova-api stop service nova-conductor stop service nova-consoleauth stop service nova-novncproxy stop service nova-scheduler stop service neutron-server stop service neutron-linuxbridge-agent stop service neutron-dhcp-agent stop service neutron-metadata-agent stop service neutron-l3-agent stop service apache2 stop

2) REMOVE THE OCATA REPOSITORY add-apt-repository --remove cloud-archive:ocata

3) ADD THE PIKE REPOSITORY add-apt-repository cloud-archive:pike

4) UPDATE PACKAGES apt-get update apt-get upgrade

5) FORCED OPENSTACK PACKAGE UPDATE apt-get install list of all packages not installed

6) ACCEPT THE INSTALLATION AND SUB-SUBSTITUTION OF THE CONFIGURATION FILES (A COPY OF THE PRESENT CONFIGURATIONS SHALL BE MADE) Choose the option: Y

In my case, the substitute archives were:

/etc/nova/nova.conf /etc/keystone/keystone-paste.ini /etc/keystone/keystone.conf /etc/neutron/l3_agent.ini /etc/neutron/neutron.conf /etc/neutron/plugins/ml2/linuxbridge_agent.ini /etc/neutron/metadata_agent.ini /etc/neutron/dhcp_agent.ini /etc/neutron/plugins/ml2/ml2_conf.ini /etc/glance/glance-registry.conf /etc/glance/glance-api.conf /etc/openstack-dashboard/local_settings.py

Note: The old configuration files have an extension: .dpkg.conf

7) COMPARE THE SUBMITTED FILES OF ITEM 6, WITH THE FILES .dpkg.conf MAKING THE CHANGES NECESSARY

8) UPDATE DATA BANK su -s /bin/sh -c "keystone-manage token_flush" keystone su -s /bin/sh -c "keystone-manage db_sync" keystone su -s /bin/sh -c "glance-manage db_sync" glance su -s /bin/sh -c "nova-manage db sync" nova su -s /bin/sh -c "nova-manage api_db sync" nova su -s /bin/sh -c "neutron-db-manage upgrade heads" neutron su -s /bin/sh -c "nova-manage db online_data_migrations" neutron

9) REMOVING UNNECESSARY PACKAGES apt autoremove

10) RESET SYSTEM reboot

UPDATE NODES COMPUTER

1) PAUSE ALL SERVICES /etc/init.d/nova-compute stop /etc/init.d/neutron-linuxbridge-agent stop /etc/init.d/neutron-linuxbridge-cleanup stop /etc/init.d/ceilometer-agent-compute stop

2) REMOVE THE OCATA REPOSITORY add-apt-repository --remove cloud-archive:ocata

3) ADD THE PIKE REPOSITORY add-apt-repository cloud-archive:pike

4) UPDATE PACKAGES apt-get update apt-get upgrade

5) FORCED OPENSTACK PACKAGE UPDATE apt-get install list of all packages not installed

6) ACCEPT THE INSTALLATION AND SUB-SUBSTITUTION OF THE CONFIGURATION FILES (A COPY OF THE PRESENT CONFIGURATIONS SHALL BE MADE) School option: Y

In my case, the substitute archives were: /etc/libvirt/libvirtd.conf /etc/ceilometer/ceilometer.conf /etc/nova/nova.conf /etc/neutron/neutron.conf /etc/neutron/plugins/ml2/linuxbridge_agent.ini

7) COMPARE THE SUBMITTED FILES OF ITEM 6, WITH THE FILES .dpkg.conf MAKING THE CHANGES NECESSARY

9) REMOVING UNNECESSARY PACKAGES apt autoremove

10) RESET SYSTEM reboot

There are a few resources that can help you plan your upgrade:
1) Superuser post on considerations for an upgrade This is from 2016, but gives you a high level overview of things to think about.
2) OpenStack Upgrades presented by Red Hat at the OpenStack Summit Sydney Some of the information is specific to Red Hat, but again, a good overview of things to think about
3) Both resources will refer to various Pike documentation. That lives here.

Upgrade is possible .But you need to plan well before doing it . Refer below links which will be useful.

https://docs.openstack.org/ironic/pik...

https://ask.openstack.org/en/question...

https://www.stratoscale.com/blog/open...