projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae | 1 | =============================== |
| 9f95a23c | 2 | Looking up Monitors through DNS |
| 7c673cae FG |
3 | =============================== |
| 4 | ||
| 5 | Since version 11.0.0 RADOS supports looking up Monitors through DNS. | |
| 6 | ||
| 7 | This way daemons and clients do not require a *mon host* configuration directive in their ceph.conf configuration file. | |
| 8 | ||
| 9 | Using DNS SRV TCP records clients are able to look up the monitors. | |
| 10 | ||
| 11 | 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. | |
| 12 | ||
| 13 | 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. | |
| 14 | ||
| 31f18b77 | 15 | |
| 20effc67 | 16 | .. confval:: mon_dns_srv_name |
| 31f18b77 | 17 | |
| 7c673cae FG |
18 | Example |
| 19 | ------- | |
| 20 | When the DNS search domain is set to *example.com* a DNS zone file might contain the following elements. | |
| 21 | ||
| 22 | First, create records for the Monitors, either IPv4 (A) or IPv6 (AAAA). | |
| 23 | ||
| 24 | :: | |
| 25 | ||
| 26 | mon1.example.com. AAAA 2001:db8::100 | |
| 27 | mon2.example.com. AAAA 2001:db8::200 | |
| 28 | mon3.example.com. AAAA 2001:db8::300 | |
| 29 | ||
| 30 | :: | |
| 31 | ||
| 32 | mon1.example.com. A 192.168.0.1 | |
| 33 | mon2.example.com. A 192.168.0.2 | |
| 34 | mon3.example.com. A 192.168.0.3 | |
| 35 | ||
| 36 | ||
| 37 | With those records now existing we can create the SRV TCP records with the name *ceph-mon* pointing to the three Monitors. | |
| 38 | ||
| 39 | :: | |
| 40 | ||
| 9f95a23c TL |
41 | _ceph-mon._tcp.example.com. 60 IN SRV 10 20 6789 mon1.example.com. |
| 42 | _ceph-mon._tcp.example.com. 60 IN SRV 10 30 6789 mon2.example.com. | |
| 43 | _ceph-mon._tcp.example.com. 60 IN SRV 20 50 6789 mon3.example.com. | |
| 7c673cae | 44 | |
| 9f95a23c | 45 | Now all Monitors are running on port *6789*, with priorities 10, 10, 20 and weights 20, 30, 50 respectively. |
| 7c673cae | 46 | |
| 9f95a23c TL |
47 | Monitor clients choose monitor by referencing the SRV records. If a cluster has multiple Monitor SRV records |
| 48 | with the same priority value, clients and daemons will load balance the connections to Monitors in proportion | |
| 49 | to the values of the SRV weight fields. | |
| 50 | ||
| 51 | For the above example, this will result in approximate 40% of the clients and daemons connecting to mon1, | |
| 52 | 60% of them connecting to mon2. However, if neither of them is reachable, then mon3 will be reconsidered as a fallback. |