The EDPM Ansible role handling OVN bridge mappings does not validate the type of the edpm_ovn_bridge_mappings variable. If a string is provided instead of a list, the role silently iterates over the string character by character, resulting in corrupted OVN configuration in OVS external_ids. This might not be a problem on freshly deployed environments immediately, but this severely affects dataplane adoptions from RHOSP17.1 to RHOSO 18.

This leads to invalid values for:

• ovn-bridge-mappings
• ovn-chassis-mac-mappings

Expected Behaviour:
If edpm_ovn_bridge_mappings is not a list, the role should fail with a clear error message.

Actual Behaviour:
When edpm_ovn_bridge_mappings is provided as a string, the role iterates over the string character by character and produces per character OVN bridge mappings and invalid MAC mappings in OVS external_ids.

[root@computer660-50 tripleo-admin]# sudo ovs-vsctl get open_vswitch . external_ids
{garp-max-timeout-sec="0", hostname=computer660-50.ctlplane.redhat.local, ovn-bridge=br-int, ovn-bridge-mappings="d,a,t,a,c,e,n,t,r,e,:,b,r,-,e,x,,,t,e,n,a,n,t,:,b,r,-,t,e,n,a,n,t,,,s,t,o,r,a,g,e,:,b,r,-,s,t,o,r,a,g,e", ovn-chassis-mac-mappings="d:2e:a2:48:ef:74:20,a:3e:de:48:ef:74:20,t:2e:6d:48:ef:74:20,c:3e:b8:48:ef:74:20,e:2e:61:48:ef:74:20,n:3e:13:48:ef:74:20,r:3e:12:48:ef:74:20,:2e:be:48:ef:74:20,b:1e:5e:48:ef:74:20,-:3e:9a:48:ef:74:20,x:0e:b9:48:ef:74:20,,:3e:6c:48:ef:74:20,s:1e:7e:48:ef:74:20,o:2e:a4:48:ef:74:20,g:0e:d9:48:ef:74:20", ovn-encap-ip="172.18.2.200", ovn-encap-tos="0", ovn-encap-type=geneve, ovn-match-northd-version=False, ovn-monitor-all=True, ovn-ofctrl-wait-before-clear="8000", ovn-openflow-probe-interval="60", ovn-remote="ssl:ovsdbserver-sb.openstack.svc:6642", ovn-remote-probe-interval="60000", rundir="/var/run/openvswitch", system-id="62de21f0-81b5-407c-b262-22dda4b55df2"} 

Steps to reproduce:

• Set edpm_ovn_bridge_mappings: "datacentre:br-ex,tenant:br-tenant,storage:br-storage"
• Run EDPM deployment
• Check OVS external_ids