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Merge pull request #10852 from wido/doc-mon-dns

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doc: Add docs about looking up Monitors through DNS

Reviewed-by: Kefu Chai <kchai@redhat.com>
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Kefu Chai 2016-11-04 19:30:29 +08:00 committed by GitHub
commit 7cd371d914
2 changed files with 48 additions and 0 deletions
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doc/rados/configuration/mon-config-ref.rst
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@ -228,6 +228,7 @@ the monitors. However, if you decide to change the monitor's IP address, you
must follow a specific procedure. See `Changing a Monitor's IP Address`_ for
details.
Monitors can also be found by clients using DNS SRV records. See `Monitor lookup through DNS`_ for details.
Cluster ID
----------
@ -854,6 +855,7 @@ Miscellaneous
.. _Monitor Keyrings: ../../../dev/mon-bootstrap#secret-keys
.. _Ceph configuration file: ../ceph-conf/#monitors
.. _Network Configuration Reference: ../network-config-ref
.. _Monitor lookup through DNS: ../mon-lookup-dns
.. _ACID: http://en.wikipedia.org/wiki/ACID
.. _Adding/Removing a Monitor: ../../operations/add-or-rm-mons
.. _Add/Remove a Monitor (ceph-deploy): ../../deployment/ceph-deploy-mon

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doc/rados/configuration/mon-lookup-dns.rst Normal file
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@ -0,0 +1,46 @@
===============================
Looking op Monitors through DNS
===============================
Since version 11.0.0 RADOS supports looking up Monitors through DNS.
This way daemons and clients do not require a *mon host* configuration directive in their ceph.conf configuration file.
Using DNS SRV TCP records clients are able to look up the monitors.
This allows for less configuration on clients and monitors. Using a DNS update clients and daemons can be made aware of changes in the monitor topology.
By default clients and daemons will look for the TCP service called *ceph-mon* which is configured by the *mon_dns_srv_name* configuration directive.
Example
-------
When the DNS search domain is set to *example.com* a DNS zone file might contain the following elements.
First, create records for the Monitors, either IPv4 (A) or IPv6 (AAAA).
::
mon1.example.com. AAAA 2001:db8::100
mon2.example.com. AAAA 2001:db8::200
mon3.example.com. AAAA 2001:db8::300
::
mon1.example.com. A 192.168.0.1
mon2.example.com. A 192.168.0.2
mon3.example.com. A 192.168.0.3
With those records now existing we can create the SRV TCP records with the name *ceph-mon* pointing to the three Monitors.
::
_ceph-mon._tcp.example.com. 60 IN SRV 10 60 6789 mon1.example.com.
_ceph-mon._tcp.example.com. 60 IN SRV 10 60 6789 mon2.example.com.
_ceph-mon._tcp.example.com. 60 IN SRV 10 60 6789 mon3.example.com.
In this case the Monitors are running on port *6789*.
The current implementation in clients and daemons does *not* honor nor respect the weight or priority set in SRV records.
All records returned will be treated equally in a Round Robin fashion.