Comment 3 for bug 1951169

More exploring has satisfied me that cinder is responding to nova, but nova does not understand the response. The following is from a packet dump between the two

===request for info=====

GET / HTTP/1.1
Host: cinder:8776
User-Agent: uwsgi keystoneauth1/4.4.0 python-requests/2.25.1 CPython/3.9.2
Accept-Encoding: gzip, deflate
Accept: */*
Connection: keep-alive
X-Auth-Token: gAAAAABhl-uasATQs6wtazUjjfnv5uvv0u4ERNGkJoaVXzo1af6aPje0pGWIR9FK68AXt_Yliyqt_kUOCo1cSIK1LvvMd7L5DrKoFzv0z8Q6TrjyqhZ3_80JHeKC83Sfevawd65UI9AYQEkgh4Hl6rqv7wTvh6A3XHdRQHcUg-fmnmfiAqyyfko
X-Service-Token: gAAAAABhl-hqLH3A8rcGoxoNY-E9Fpe1wQRMj9f8CHXehaZ8KqKik8N4Y2EtXVy35MBcSxMQCze72s5jVooliOwIseLcIM34bRsuZEiUfGOy3yS4E4AtnUJTaRw0HFrEuSpFLSzORTvcXXtgGqX256lXPb7-cwY-iM-pd0dGxA_ZowZhNqS03mY

HTTP/1.1 300 Multiple Choices
Content-Type: application/json
OpenStack-API-Version: volume 3.0
Vary: OpenStack-API-Version
Connection: close

{"versions": [{"id": "v3.0", "status": "CURRENT", "version": "3.66", "min_version": "3.0", "updated": "2021-09-16T00:00:00Z", "links": [{"rel": "describedby", "type": "text/html", "href": "https://docs.openstack.org/"}, {"rel": "self", "href": "http://cinder:8776/v3/"}], "media-types": [{"base": "application/json", "type": "application/vnd.openstack.volume+json;version=3"}]}]}

====request for to attach disk=======

POST /v3/78d0093b66f547d2be2b78e496f9d795/attachments HTTP/1.1
Host: cinder:8776
User-Agent: python-cinderclient
Accept-Encoding: gzip, deflate
Accept: application/json
Connection: keep-alive
X-OpenStack-Request-ID: req-9c4abd38-9f76-4317-a014-a7ac74876411
OpenStack-API-Version: volume 3.44
X-Auth-Token: gAAAAABhl-uasATQs6wtazUjjfnv5uvv0u4ERNGkJoaVXzo1af6aPje0pGWIR9FK68AXt_Yliyqt_kUOCo1cSIK1LvvMd7L5DrKoFzv0z8Q6TrjyqhZ3_80JHeKC83Sfevawd65UI9AYQEkgh4Hl6rqv7wTvh6A3XHdRQHcUg-fmnmfiAqyyfko
X-Service-Token: gAAAAABhl-hqLH3A8rcGoxoNY-E9Fpe1wQRMj9f8CHXehaZ8KqKik8N4Y2EtXVy35MBcSxMQCze72s5jVooliOwIseLcIM34bRsuZEiUfGOy3yS4E4AtnUJTaRw0HFrEuSpFLSzORTvcXXtgGqX256lXPb7-cwY-iM-pd0dGxA_ZowZhNqS03mY
Content-Type: application/json
Content-Length: 147

{"attachment": {"volume_uuid": "42caf199-aa77-4987-a1ab-0dd79f5aa952", "connector": null, "instance_uuid": "746e8192-8561-4019-86df-c5179d805dea"}}HTTP/1.1 200 OK
Content-Type: application/json
x-compute-request-id: req-0c90c8a1-9d23-475d-b232-32388c981c8a
OpenStack-API-Version: volume 3.44
Vary: OpenStack-API-Version
x-openstack-request-id: req-0c90c8a1-9d23-475d-b232-32388c981c8a
Connection: close

{"attachment": {"id": "bee7db8c-8b8d-4548-9ce7-1101eef164e1", "status": "reserved", "instance": "746e8192-8561-4019-86df-c5179d805dea", "volume_id": "42caf199-aa77-4987-a1ab-0dd79f5aa952", "attached_at": "", "detached_at": "", "attach_mode": "null", "connection_info": {}}}

====

after all that nova gives the error

publicURL endpoint for volumev3 service in regionOne region not found

Can't be.