projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 05a536ef TL |
1 | .. _mon-dns-lookup: |
| 2 | ||
| 7c673cae | 3 | =============================== |
| 9f95a23c | 4 | Looking up Monitors through DNS |
| 7c673cae FG |
5 | =============================== |
| 6 | ||
| 1e59de90 TL |
7 | Since Ceph version 11.0.0 (Kraken), RADOS has supported looking up monitors |
| 8 | through DNS. | |
| 7c673cae | 9 | |
| 1e59de90 TL |
10 | The addition of the ability to look up monitors through DNS means that daemons |
| 11 | and clients do not require a *mon host* configuration directive in their | |
| 12 | ``ceph.conf`` configuration file. | |
| 7c673cae | 13 | |
| 1e59de90 TL |
14 | With a DNS update, clients and daemons can be made aware of changes |
| 15 | in the monitor topology. To be more precise and technical, clients look up the | |
| 16 | monitors by using ``DNS SRV TCP`` records. | |
| 7c673cae | 17 | |
| 1e59de90 TL |
18 | By default, clients and daemons look for the TCP service called *ceph-mon*, |
| 19 | which is configured by the *mon_dns_srv_name* configuration directive. | |
| 7c673cae | 20 | |
| 31f18b77 | 21 | |
| 20effc67 | 22 | .. confval:: mon_dns_srv_name |
| 31f18b77 | 23 | |
| 7c673cae FG |
24 | Example |
| 25 | ------- | |
| 26 | When the DNS search domain is set to *example.com* a DNS zone file might contain the following elements. | |
| 27 | ||
| 28 | First, create records for the Monitors, either IPv4 (A) or IPv6 (AAAA). | |
| 29 | ||
| 30 | :: | |
| 31 | ||
| 32 | mon1.example.com. AAAA 2001:db8::100 | |
| 33 | mon2.example.com. AAAA 2001:db8::200 | |
| 34 | mon3.example.com. AAAA 2001:db8::300 | |
| 35 | ||
| 36 | :: | |
| 37 | ||
| 38 | mon1.example.com. A 192.168.0.1 | |
| 39 | mon2.example.com. A 192.168.0.2 | |
| 40 | mon3.example.com. A 192.168.0.3 | |
| 41 | ||
| 42 | ||
| 43 | With those records now existing we can create the SRV TCP records with the name *ceph-mon* pointing to the three Monitors. | |
| 44 | ||
| 45 | :: | |
| 46 | ||
| 9f95a23c TL |
47 | _ceph-mon._tcp.example.com. 60 IN SRV 10 20 6789 mon1.example.com. |
| 48 | _ceph-mon._tcp.example.com. 60 IN SRV 10 30 6789 mon2.example.com. | |
| 49 | _ceph-mon._tcp.example.com. 60 IN SRV 20 50 6789 mon3.example.com. | |
| 7c673cae | 50 | |
| 9f95a23c | 51 | Now all Monitors are running on port *6789*, with priorities 10, 10, 20 and weights 20, 30, 50 respectively. |
| 7c673cae | 52 | |
| 9f95a23c TL |
53 | Monitor clients choose monitor by referencing the SRV records. If a cluster has multiple Monitor SRV records |
| 54 | with the same priority value, clients and daemons will load balance the connections to Monitors in proportion | |
| 55 | to the values of the SRV weight fields. | |
| 56 | ||
| 57 | For the above example, this will result in approximate 40% of the clients and daemons connecting to mon1, | |
| 58 | 60% of them connecting to mon2. However, if neither of them is reachable, then mon3 will be reconsidered as a fallback. |