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https://github.com/ceph/ceph
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57 lines
2.1 KiB
ReStructuredText
57 lines
2.1 KiB
ReStructuredText
===============================
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Looking up Monitors through DNS
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===============================
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Since version 11.0.0 RADOS supports looking up Monitors through DNS.
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This way daemons and clients do not require a *mon host* configuration directive in their ceph.conf configuration file.
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Using DNS SRV TCP records clients are able to look up the monitors.
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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.
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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.
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``mon dns srv name``
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:Description: the service name used querying the DNS for the monitor hosts/addresses
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:Type: String
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:Default: ``ceph-mon``
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Example
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-------
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When the DNS search domain is set to *example.com* a DNS zone file might contain the following elements.
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First, create records for the Monitors, either IPv4 (A) or IPv6 (AAAA).
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::
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mon1.example.com. AAAA 2001:db8::100
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mon2.example.com. AAAA 2001:db8::200
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mon3.example.com. AAAA 2001:db8::300
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::
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mon1.example.com. A 192.168.0.1
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mon2.example.com. A 192.168.0.2
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mon3.example.com. A 192.168.0.3
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With those records now existing we can create the SRV TCP records with the name *ceph-mon* pointing to the three Monitors.
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::
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_ceph-mon._tcp.example.com. 60 IN SRV 10 20 6789 mon1.example.com.
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_ceph-mon._tcp.example.com. 60 IN SRV 10 30 6789 mon2.example.com.
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_ceph-mon._tcp.example.com. 60 IN SRV 20 50 6789 mon3.example.com.
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Now all Monitors are running on port *6789*, with priorities 10, 10, 20 and weights 20, 30, 50 respectively.
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Monitor clients choose monitor by referencing the SRV records. If a cluster has multiple Monitor SRV records
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with the same priority value, clients and daemons will load balance the connections to Monitors in proportion
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to the values of the SRV weight fields.
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For the above example, this will result in approximate 40% of the clients and daemons connecting to mon1,
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60% of them connecting to mon2. However, if neither of them is reachable, then mon3 will be reconsidered as a fallback.
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