ceph/doc/rados/operations/change-mon-elections.rst

   1 .. _changing_monitor_elections:
   2
   3 =====================================
   4 Configure Monitor Election Strategies
   5 =====================================
   6
   7 By default, the monitors will use the ``classic`` mode. We
   8 recommend that you stay in this mode unless you have a very specific reason.
   9
  10 If you want to switch modes BEFORE constructing the cluster, change
  11 the ``mon election default strategy`` option. This option is an integer value:
  12
  13 * 1 for "classic"
  14 * 2 for "disallow"
  15 * 3 for "connectivity"
  16
  17 Once your cluster is running, you can change strategies by running ::
  18
  19   $ ceph mon set election_strategy {classic|disallow|connectivity}
  20
  21 Choosing a mode
  22 ===============
  23 The modes other than classic provide different features. We recommend
  24 you stay in classic mode if you don't need the extra features as it is
  25 the simplest mode.
  26
  27 The disallow Mode
  28 =================
  29 This mode lets you mark monitors as disallowd, in which case they will
  30 participate in the quorum and serve clients, but cannot be elected leader. You
  31 may wish to use this if you have some monitors which are known to be far away
  32 from clients.
  33 You can disallow a leader by running ::
  34
  35   $ ceph mon add disallowed_leader {name}
  36
  37 You can remove a monitor from the disallowed list, and allow it to become
  38 a leader again, by running ::
  39
  40   $ ceph mon rm disallowed_leader {name}
  41
  42 The list of disallowed_leaders is included when you run ::
  43
  44   $ ceph mon dump
  45
  46 The connectivity Mode
  47 =====================
  48 This mode evaluates connection scores provided by each monitor for its
  49 peers and elects the monitor with the highest score. This mode is designed
  50 to handle network partitioning or *net-splits*, which may happen if your cluster
  51 is stretched across multiple data centers or otherwise has a non-uniform
  52 or unbalanced network topology.
  53
  54 This mode also supports disallowing monitors from being the leader
  55 using the same commands as above in disallow.
  56
  57 Examining connectivity scores
  58 =============================
  59 The monitors maintain connection scores even if they aren't in
  60 the connectivity election mode. You can examine the scores a monitor
  61 has by running ::
  62
  63   ceph daemon mon.{name} connection scores dump
  64
  65 Scores for individual connections range from 0-1 inclusive, and also
  66 include whether the connection is considered alive or dead (determined by
  67 whether it returned its latest ping within the timeout).
  68
  69 While this would be an unexpected occurrence, if for some reason you experience
  70 problems and troubleshooting makes you think your scores have become invalid,
  71 you can forget history and reset them by running ::
  72
  73   ceph daemon mon.{name} connection scores reset
  74
  75 While resetting scores has low risk (monitors will still quickly determine
  76 if a connection is alive or dead, and trend back to the previous scores if they
  77 were accurate!), it should also not be needed and is not recommended unless
  78 requested by your support team or a developer.