The loss of a management node or SQL/API node should not bring down the cluster.
The STOP command has a built-in safety feature, which you can use to find out whether the loss of a given data node would bring down the cluster, like this:
ndb_mgm> SHOW
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=5 @127.0.0.1 (mysql-5.7.23 ndb-7.6.8, Nodegroup: 0, *)
id=6 @127.0.0.1 (mysql-5.7.23 ndb-7.6.8, Nodegroup: 0)
[ndb_mgmd(MGM)] 1 node(s)
id=50 @127.0.0.1 (mysql-5.7.23 ndb-7.6.8)
[mysqld(API)] 2 node(s)
id=100 (not connected, accepting connect from 127.0.0.1)
id=101 (not connected, accepting connect from any host)
ndb_mgm> 5 STOP
Node 5: Node shutdown initiated
Node 5: Node shutdown completed.
Node 5 has shutdown.
ndb_mgm> SHOW
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=5 (not connected, accepting connect from 127.0.0.1)
id=6 @127.0.0.1 (mysql-5.7.23 ndb-7.6.8, Nodegroup: 0, *)
[ndb_mgmd(MGM)] 1 node(s)
id=50 @127.0.0.1 (mysql-5.7.23 ndb-7.6.8)
[mysqld(API)] 2 node(s)
id=100 (not connected, accepting connect from 127.0.0.1)
id=101 (not connected, accepting connect from any host)
ndb_mgm> 6 stop
Node 6: Node shutdown aborted
Shutdown failed.
* 2002: Stop failed
* Node shutdown would cause system crash: Permanent error: Application error
ndb_mgm> show
Cluster Configuration
---------------------
[ndbd(NDB)] 2 node(s)
id=5 (not connected, accepting connect from 127.0.0.1)
id=6 @127.0.0.1 (mysql-5.7.23 ndb-7.6.8, Nodegroup: 0, *)
[ndb_mgmd(MGM)] 1 node(s)
id=50 @127.0.0.1 (mysql-5.7.23 ndb-7.6.8)
[mysqld(API)] 2 node(s)
id=100 (not connected, accepting connect from 127.0.0.1)
id=101 (not connected, accepting connect from any host)
cheers
Jon Stephens
MySQL Documentation Team @ Oracle
MySQL Dev Zone
MySQL Server Documentation
Oracle