Perform the removal

When you remove any Kudu masters from a multi-master deployment, you need to rewrite the Raft configuration on the remaining masters, remove data and WAL directories from the unwanted masters, and finaly modify the value of the tserver_master_addrs configuration parameter for the tablet servers to remove the unwanted masters. You need to bring the Kudu clusters down. Therefore, identify at least a one-hour maintenance window for this task.

  1. Rewrite the Raft configuration on the remaining masters to include only the remaining masters.
    $ sudo -u kudu kudu local_replica cmeta rewrite_raft_config --fs_wal_dir=<master_wal_dir> [--fs_data_dirs=<master_data_dir>] <tablet_id> <all_masters>
    master_data_dir

    The existing master’s previously recorded data directory

    tablet_id

    This must be set to the string, 00000000000000000000000000000000.

    all_masters

    A space-separated list of masters, both new and existing. Each entry in the list must be a string of the form <uuid>:<hostname>:<port>.

    uuid

    The master’s previously recorded UUID.

    hostname

    The master’s previously recorded hostname or alias.

    port

    The master’s previously recorded RPC port number.

    For example:
    $ sudo -u kudu kudu local_replica cmeta rewrite_raft_config --fs_wal_dir=/data/kudu/master/wal --fs_data_dirs=/data/kudu/master/data 00000000000000000000000000000000 4aab798a69e94fab8d77069edff28ce0:master-1:7051 f5624e05f40649b79a757629a69d061e:master-2:7051 988d8ac6530f426cbe180be5ba52033d:master-3:7051
  2. Remove the data directories and WAL directory on the unwanted masters. This is a precaution to ensure that they cannot start up again and interfere with the new multi-master deployment.
  3. Modify the value of the master_addresses configuration parameter for the masters of the new multi-master deployment. See Apache Kudu configuration for the steps to modify a configuration parameter. If migrating to a single-master deployment, the master_addresses flag should be omitted entirely.
  4. Start all of the masters that were not removed.
  5. Modify the value of the tserver_master_addrs configuration parameter for the tablet servers to remove any unwanted masters. See Apache Kudu configuration for the steps to modify a configuration parameter.
  6. Start all of the tablet servers.
To verify that all masters are working properly, consider performing the following checks:
  • Using a browser, visit each master’s web UI and navigate to the /masters page. All the masters should now be listed there with one master in the LEADER role and the others in the FOLLOWER role. The contents of /masters on each master should be the same.

  • Run a Kudu system check (ksck) on the cluster using the kudu command line tool.