Every time I teach the MySQL Cluster architecture, someone
inevitably asks "Isn't the management node (ndb_mgmd) a single
point of failure?" The short answer: no. The management node is
not a SPOF because the cluster can continue without it. However,
it's inconvenient if your management node is down because the
management node does several things such as:
-
- Provide status information about the cluster and allow you to
use the ndb_mgm for various maintenance tasks like taking a hot
backup
- Own the cluster config file (therefore it must be running to
start a node)
- Arbitration in case of a potential split-brain
- Logging
So while the management node can be down, it is nice to have a
redundant one for failover. This is very easy to do:
-
- Add 2 [NDB_MGMD] sections to …