Description of problem:
In step 20.3.8 of the official guide[1] about the controller replacement there is a check to remove the old controller in the raft cluster for the southbound OVN database:
~~~
ssh tripleo-admin@<controller_ip> sudo podman exec ovn_cluster_north_db_server ovs-appctl -t /var/run/ovn/ovnnb_db.ctl cluster/status OVN_Southbound 2>/dev/null|grep -A4 Servers:
~~~
This command return always a void output because there is a type error, if we don't redirect the error to null we can see it clearly:
~~~
[tripleo-admin@controller-1 ~]$ sudo podman exec ovn_cluster_north_db_server ovs-appctl -t /var/run/ovn/ovnnb_db.ctl cluster/status OVN_Southbound 
unknown cluster
ovs-appctl: /var/run/ovn/ovnnb_db.ctl: server returned an error
~~~
We should target southbound db instance of northbound:
~~~
[tripleo-admin@controller-1 ~]$ sudo podman exec ovn_cluster_north_db_server ovs-appctl -t /var/run/ovn/ovnsb_db.ctl cluster/status OVN_Southbound 
d670
Name: OVN_Southbound
Cluster ID: 812c (812c8a42-2f65-43c3-b790-2fd4e52076d5)
Server ID: d670 (d670116b-97e3-4383-a375-eba0971427c6)
Address: tcp:172.17.1.133:6644
Status: cluster member
Role: follower
Term: 23064
Leader: 48e3
Vote: 48e3

Last Election started 7669964 ms ago, reason: leadership_transfer
Last Election won: 7669936 ms ago
Election timer: 16000
Log: [1150, 1151]
Entries not yet committed: 0
Entries not yet applied: 0
Connections: ->48e3 ->5d8a <-48e3 <-5d8a
Disconnections: 0
Servers:
    48e3 (48e3 at tcp:172.17.1.59:6644) last msg 4873 ms ago
    5d8a (5d8a at tcp:172.17.1.36:6644) last msg 6757556 ms ago
    d670 (d670 at tcp:172.17.1.133:6644) (self)
~~~

So I will rewrite the command in this way:
~~~
ssh tripleo-admin@<controller_ip> sudo podman exec ovn_cluster_south_db_server ovs-appctl -t /var/run/ovn/ovnsb_db.ctl cluster/status OVN_Southbound 2>/dev/null|grep -A4 Servers:
~~~

Note: why do we redirect the error output to null? should it not be better to see it on the screen when we don't put the output in a variable or use it directly?


[1] https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/17.1/html/installing_and_managing_red_hat_openstack_platform_with_director/assembly_replacing-controller-nodes
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