Restricting write access to a MySQL Cluster with single-user mode
Most MySQL Clusters will have more than one SQL node (mysqld process) as well as the option for other API nodes such as ndb_restore to connect to the cluster. Occasionally, it is essential for only one API node to access the cluster. MySQL Cluster has a single-user mode which, allows you to temporarily specify only a single API node that may execute the queries against the cluster.
In this recipe, we will use an example cluster with two SQL nodes, nodeIDs 13 and 14, execute a query against both the nodes, enter single-user mode, repeat the experiment, and finish by verifying that once the single user mode is exited, the query works as it did at the beginning of the exercise.
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