Add reserve nodes to existing deployment

This article explains how to add nodes to an existing deployment and define them as reserve nodes.

You can add one or more reserve nodes to an existing deployment by cloning one of the nodes in the deployment. The new nodes are automatically started up as inactive (database not running) and can then be added to the cluster as reserve nodes.

You cannot remove active nodes from an Exasol database. If you want to reduce the number of active nodes in a cluster, you must delete the database and the data volume and create a new deployment.

The following examples use the c4 and confd_client command-line tools in a Linux terminal. To learn more about these tools, see Exasol Deployment Tool (c4) and ConfD.

Prerequisites

An existing Exasol deployment.

Set the config path

When you make changes to an existing deployment you must use the same configuration that was used when creating the deployment. If the configuration file that was used is not named config and/or is not located in the current working directory (on the host where you run c4), you must prepend the c4 commands with the path to the configuration file using CCC_CONFIG=<path-to-config>.

Example:
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CCC_CONFIG=./path_to_config/my_config c4 <command>

In the following examples, the default configuration file is used.

Procedure

Step 1: Connect to COS

Connect to the cluster operating system (COS) using c4 connect -i PLAY_ID -s cos.

Example:
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./c4 connect -i c3275f84 -s cos

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

This procedure uses the command-line tool confd_client, which is available on all database nodes. You can also access ConfD through XML-RPC in your own Python programs. For more information, see ConfD.

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

Step 2: Add the nodes to the deployment

To add the nodes to the deployment, use the ConfD job infra_instances_add with the following parameters:

Parameter name Data type Description
nid integer ID of an existing node. The configuration of this node will be cloned to create the new nodes.
num_nodes integer The number of nodes that you want to create.
Example:

This example adds two nodes by cloning the node with ID 11.

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confd_client infra_instances_add nid: 11 num_nodes: 2

The added nodes will automatically start up and reach deployment stage c (COS service running, database not running). At this point the nodes are not yet part of the cluster.

Step 3: Add the nodes to the cluster

To add the new nodes to the cluster as reserve nodes, use the ConfD job db_add_reserve_nodes with the following parameters:

Parameter Name Data type Description
db_name string The name of the database
node_list list List of node IDs (integers) to add as reserve nodes
Example:
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confd_client db_add_reserve_nodes db_name: MY_DATABASE node_list: '[15, 16]'

Step 4: Verify that the nodes are added

To verify that the nodes are added, use the ConfD job node_list.

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confd_client node_list