doc/rados: document manually passing search domain

Document how to manually pass the search domain to "mon_dns_srv_name" in
doc/rados/configuration/mon-lookup-dns.rst.

This commit is made in response to a request by Lander Duncan that was made on the [ceph-users] mailing list, and can be seen here: https://lists.ceph.io/hyperkitty/list/ceph-users@ceph.io/thread/F7V4CWLIYCAJ4JXI2JLNY6QPCFPR4SLA/

Co-authored-by: Anthony D'Atri <anthony.datri@gmail.com>
Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit 98938a0312dd0c8e0b293ed9aa2e0760cc9619fa)

diff --git a/doc/rados/configuration/mon-lookup-dns.rst b/doc/rados/configuration/mon-lookup-dns.rst
index 129a083c437fb8c2de7bf66c7afb55474631c06a..0e2ee22e4155a5db31a1fb3765690f8f0aa49fc0 100644 (file)
--- a/doc/rados/configuration/mon-lookup-dns.rst
+++ b/doc/rados/configuration/mon-lookup-dns.rst
@@ -21,6 +21,13 @@ which is configured by the *mon_dns_srv_name* configuration directive.
 
 .. confval:: mon_dns_srv_name
 
+.. note:: Instead of using a DNS search domain, it is possible to manually
+   designate the search domain by passing the search domain's name followed by
+   an underscore to ``mon_dns_srv_name``. The syntax for this is
+   ``<service-name>_<upper-level-domain>``. For example, passing
+   ``ceph-mon_example.com`` will direct Ceph to look for the ``SRV`` record at
+   ``_ceph-mon._tcp.example.com``.
+
 Example
 -------
 When the DNS search domain is set to *example.com* a DNS zone file might contain the following elements.