The variable altnames is used by this task.

Since the value will change on the default. It needs to change here also.

roles/vault/tasks/bootstrap/gen_vault_certs.yml

@@ -2,7 +2,7 @@
 - include: ../shared/issue_cert.yml
   vars:
     issue_cert_common_name: "{{ vault_pki_mounts.vault.roles[0].name }}"
-    issue_cert_alt_names: "{{ groups.vault + ['localhost'] + vault_ca_options.vault.altnames|default() }}"
+    issue_cert_alt_names: "{{ groups.vault + ['localhost'] + vault_ca_options.vault.alt_names|default() }}"
     issue_cert_hosts: "{{ groups.vault }}"
     issue_cert_ip_sans: >-
         [