Description of problem:
During an attempt to migrate from ML2OVS to ML2OVN after OSP13->OSP16.1 FFU I found that some of the ansible tasks fail (e.g. when running 'ovn_migration.sh setup-mtu-t1' command)


Tuesday 25 August 2020  13:58:35 -0400 (0:00:00.954)       0:00:06.349 ******** 
changed: [controller-2] => {"changed": true, "cmd": "docker ps | grep neutron_dhcp | awk '{print $1}'", "delta": "0:00:00.008172", "end": "2020-08-25 17:58:34.838797", "rc": 0, "start": "2020-08-25 17:58:34.830625", "stderr": "/bin/sh: docker: command not found", "stderr_lines": ["/bin/sh: docker: command not found"], "stdout": "", "stdout_lines": []}
changed: [controller-1] => {"changed": true, "cmd": "docker ps | grep neutron_dhcp | awk '{print $1}'", "delta": "0:00:00.008415", "end": "2020-08-25 17:58:35.136291", "rc": 0, "start": "2020-08-25 17:58:35.127876", "stderr": "/bin/sh: docker: command not found", "stderr_lines": ["/bin/sh: docker: command not found"], "stdout": "", "stdout_lines": []}
changed: [controller-0] => {"changed": true, "cmd": "docker ps | grep neutron_dhcp | awk '{print $1}'", "delta": "0:00:00.008463", "end": "2020-08-25 17:58:35.440127", "rc": 0, "start": "2020-08-25 17:58:35.431664", "stderr": "/bin/sh: docker: command not found", "stderr_lines": ["/bin/sh: docker: command not found"], "stdout": "", "stdout_lines": []}

TASK [Restart neutron dhcp agent] ************************************************************************************************************************************************************
task path: /home/stack/ovn_migration/playbooks/reduce-dhcp-renewal-time.yml:22
Tuesday 25 August 2020  13:58:36 -0400 (0:00:00.862)       0:00:07.211 ******** 
fatal: [controller-0]: FAILED! => {"changed": false, "cmd": "docker restart", "msg": "[Errno 2] No such file or directory: b'docker': b'docker'", "rc": 2}
...ignoring
fatal: [controller-1]: FAILED! => {"changed": false, "cmd": "docker restart", "msg": "[Errno 2] No such file or directory: b'docker': b'docker'", "rc": 2}
...ignoring
fatal: [controller-2]: FAILED! => {"changed": false, "cmd": "docker restart", "msg": "[Errno 2] No such file or directory: b'docker': b'docker'", "rc": 2}
...ignoring
META: ran handlers
META: ran handlers

PLAY RECAP ***********************************************************************************************************************************************************************************
controller-0               : ok=4    changed=2    unreachable=0    failed=0    skipped=0    rescued=0    ignored=1   
controller-1               : ok=4    changed=2    unreachable=0    failed=0    skipped=0    rescued=0    ignored=1   
controller-2               : ok=4    changed=2    unreachable=0    failed=0    skipped=0    rescued=0    ignored=1 


This happened because podman-docker package was not installed.
Workaround is to install the podman-docker package which emulates docker CLI using podman.

We need either fix migration scripts to use podman command instead of docker or mention in documentation that user need to install this dependency.



Version-Release number of selected component (if applicable):
RHOS-16.1-RHEL-8-20200813.n.0
python3-networking-ovn-migration-tool-7.2.1-0.20200611133439.15f2281.el8ost.noarch

How reproducible:
Tried migration after FFU once and the issue occurred

Steps to Reproduce:
Perform FFU from 13 to 16.1 when using ML2OVS mechanism driver
Try to migrate from ML2OVS to ML2OVN

Actual results:
Important tasks (like containers restart) are failing because 'docker' command is missing. 

Expected results:
No fails of important tasks like container restart etc.

Additional info: