Add Reserve Node

This section explains how to define an existing node as a reserve node.

Reserve nodes are standby nodes that will take over if an active node in the cluster fails. For more information about the failover mechanisms in Exasol, see Fail Safety.

This procedure is carried out using ConfD.

Prerequisites

The node to be defined as a reserve node must already be added to the cluster and configured accordingly.

Procedure

The following examples use ConfD through the command-line tool confd_client, which is available on all database nodes. For more information, see ConfD.

Placeholder values are indicated with UPPERCASE characters. Replace the placeholders with your own values.

  1. Connect to EXAClusterOS (COS) using c4 connect -t <DEPLOYMENT>[.<NODE>]/cos. For example:

    c4 connect -t 1/cos

    In most cases it does not matter on which node you access ConfD. If you do not specify a node, c4 will connect to the first active node in the deployment. The command prompt in COS indicates which node you are connected to: 

    [root@n11 ~]#

    For more information about how to use c4 connect, see How to use c4.

  2. To stop the database, use the ConfD job db_stop. For example:

    confd_client db_stop db_name: MY_DATABASE

  3. To verify that the database has stopped, use the ConfD job db_state. If the result is setup, the database is stopped. For example:

    confd_client db_state db_name: MY_DATABASE
    ...
    Result:
    'setup'

  4. To add one or more nodes as reserve nodes, use the ConfD job db_add_reserve_nodes. For example: 

    confd_client db_add_reserve_nodes db_name: MY_DATABASE node_list: '[16, 17]'

  5. Start the database using the ConfD job db_start. For example:

    confd_client db_start db_name: MY_DATABASE

Verification

To verify that the reserve nodes have been added, use the ConfD job node_list. 

confd_client node_list