Add reserve nodes to existing deployment

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

Prerequisites

  • An existing Exasol 8 deployment.

  • The parameter CCC_HOST_CLEANUP must be set to false in the configuration that was used to create the deployment. If you created the deployment with CCC_HOST_CLEANUP=true, you will not be able to add nodes using this method.

This method should only be used if you already have a deployment and want to add reserve nodes to it. If you have not created the deployment yet, use the procedure in Define reserve nodes when creating a deployment.

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

Setting the config path

When you make changes to an existing deployment you must use the same configuration that was used when creating the deployment. Unless that configuration is in the current working directory (on the host where you run c4), you must prepend the c4 commands with the path to the configuration using CCC_CONFIG=<path-to-config>. For example:

CCC_CONFIG=./path_to_config/my_config c4 <command>

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

Procedure

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

Step 1: Prepare the hosts

Prepare the new host machines according to the hardware, network, and operating system requirements described in System Requirements.

Step 2: Reserve the nodes in the configuration

On a jump host that has SSH access to the cluster nodes, run the c4 command CCC_CONFIG=config c4 host reserve <PLAY_ID> with the following command-line parameters:

Parameter Description

--ccc-host-reserved-addrs

Private IP address of a host that you want to add to the cluster.

You must repeat the parameter for each additional host, separated by a space: --ccc-host-reserved-addrs <host_1> --ccc-host-reserved-addrs <host_2> and so on.
--ccc-host-reserved-external-addrs

Public IP address of a host that you want to add to the cluster.

You must repeat the parameter for each additional host, separated by a a space: --ccc-host-reserved-external-addrs <host_1> --ccc-host-reserved-external-addrs <host_2> and so on.

This parameter is only required if the existing data nodes were deployed with public IP addresses (CCC_HOST_EXTERNAL_ADDRS was set at deploy time).

These parameters must be defined on the command line as part of the c4 host reserve command. They cannot be defined in the configuration file or as environment variables before the command.

For more details about parameter formats, see Parameters in c4.

To find the PLAY_ID and other details of of the deployment, use c4 ps.

Example

Determine the play ID of the deployment:

CCC_CONFIG=config c4 ps
      N  PLAY_ID   NODE  MEDIUM  INSTANCE     EXTERNAL_IP     INTERNAL_IP  STAGE  STATE      UPTIME    TTL
  ┌─  1  3a4a7d8d  11    host    c5d.2xlarge  203.0.113.11    10.0.0.11    d      running    04:35:16  +∞
  │   1  3a4a7d8d  12    host    c5d.2xlarge  203.0.113.12    10.0.0.11    d      running    04:35:16  +∞
  └─  1  3a4a7d8d  13    host    c5d.2xlarge  203.0.113.13    10.0.0.13    d      running    04:35:15  +∞

Reserve private and public IP addresses for the new nodes:

CCC_CONFIG=config c4 host reserve --ccc-host-reserved-addrs 10.0.0.14 --ccc-host-reserved-addrs 10.0.0.15 --ccc-host-reserved-external-addrs 203.0.113.14 --ccc-host-reserved-external-addrs 203.0.113.15 3a4a7d8d 

Step 3: Connect to COS

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

./c4 connect -t 1.11/cos

If you do not specify a node, c4 will connect to the first active node in the deployment.

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

The following examples use ConfD through 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 4: 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.

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 5: 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:
confd_client db_add_reserve_nodes db_name: MY_DATABASE node_list: '[15, 16]'

Step 6: Verify that the nodes are added

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

confd_client node_list