Add reserve nodes to existing deployment
Learn 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
This operation must be carried out from a jump host that has SSH access to the cluster nodes.
Preparations
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:
CCC_CONFIG=./path_to_config/my_config c4 <command>In the following examples, the default configuration file path is used.
In AWS native cloud deployments of Exasol, skip to Step 2: Connect to COS.
Download Exasol to the cloned node
If the deployment was created with the configuration parameter CCC_HOST_CLEANUP unset (empty) or explicitly set to true, you must download the software package of the currently installed Exasol version into the home directory of the node that you will clone.
If the deployment was created with the configuration parameter CCC_HOST_CLEANUP=false, the Exasol installation package should already be present on the cloned node. In this case you can skip this step.
Example:
-
Check the value of
CCC_HOST_CLEANUPCopyCCC_CONFIG=config ./c4 config -K ccc_host_cleanup
Found 1 results for query `ccc_host_cleanup`:
CCC_HOST_CLEANUP (bool)
Default value : true
Current value : [empty]
... -
Check the Exasol version
CopyCCC_CONFIG=config ./c4 ps
N PLAY_ID NODE MEDIUM INSTANCE DB_VERSION EXTERNAL_IP INTERNAL_IP STAGE STATE UPTIME TTL
┌─ 1 c3275f84 11 host - 8.34.0 203.0.113.11 10.0.0.11 d running 04:35:16 +∞
... -
Download Exasol to the node that you will clone (node 11 in this case)
CopyCCC_CONFIG=config ./c4 connect -t 1.11/host
VERSION=8.34.0
curl https://x-up.s3.amazonaws.com/releases/exasol/linux/x86_64/$VERSION/exasol-$VERSION.tar.gz -O
When the Exasol package has been downloaded, use Control+D to disconnect from the host.
Prepare the new hosts
Prepare the new physical or virtual host as needed depending on your existing deployment environment. For details about the hardware and operating system requirements, see System requirements.
The nodes in the cluster should be assigned consecutive and evenly spaced static IPv4 addresses in the same subnet.
Procedure
Step 1: Reserve the IP addresses in the configuration
On the jump host, run CCC_CONFIG=config c4 host reserve <PLAY_ID> with the following parameters:
| Parameter | Description |
|---|---|
|
|
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. For example: |
--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. For example: This parameter is only required if the existing data nodes were deployed with public IP addresses ( |
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 Deployment configuration parameters.
Example:
Get the play ID and other details for the deployment:
CCC_CONFIG=config c4 ps
N PLAY_ID NODE MEDIUM INSTANCE DB_VERSION EXTERNAL_IP INTERNAL_IP STAGE STATE UPTIME TTL
┌─ 1 c3275f84 11 host - 8.34.0 203.0.113.11 10.0.0.11 d running 04:35:16 +∞
│ 1 c3275f84 12 host - 8.34.0 203.0.113.12 10.0.0.11 d running 04:35:16 +∞
└─ 1 c3275f84 13 host - 8.34.0 203.0.113.13 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 c3275f84 Step 2: Connect to COS
Connect to the cluster operating system (COS) using c4 connect -i PLAY_ID -s cos.
Example:
./c4 connect -i c3275f84 -s cosTo find the play ID, you can use c4 ps.
For more information about how to use c4 commands, see How to use c4.
This procedure uses 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 3: Add the new 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: 2The 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 4: Add reserve 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: '[14, 15]'Step 5: Update the configuration on the jump host
This step is required because the previous steps will not update the configuration on the jump host, only on the nodes.
In the configuration file on the jump host, add the private/public IP addresses of the new nodes in CCC_HOST_ADDRS, CCC_HOST_EXTERNAL_ADDRS, and add the number of reserve nodes to add in the parameter CCC_PLAY_RESERVE_NODES.
Example:
Original configuration
...
CCC_HOST_ADDRS="10.0.0.11 10.0.0.12 10.0.0.13"
CCC_HOST_EXTERNAL_ADDRS="203.0.113.11 203.0.113.12 203.0.113.13"
...New configuration (adding two reserve nodes)
...
CCC_HOST_ADDRS="10.0.0.11 10.0.0.12 10.0.0.13 10.0.0.14 10.0.0.15"
CCC_HOST_EXTERNAL_ADDRS="203.0.113.11 203.0.113.12 203.0.113.13 203.0.113.14 203.0.113.15"
CCC_PLAY_RESERVE_NODES=2
...If the deployment has the node IDs configured in CCC_HOST_NODE_IDS, the parameter in the configuration on the jump host must be updated to match the parameter in the deployment. You can find out the node IDs using the ConfD job node_list.
Example:
confd_client node_list | grep '^ id'
id: '10'
id: '11'
id: '12'
id: '13'
id: '14'
id: '15'...
CCC_HOST_ADDRS="10.0.0.11 10.0.0.12 10.0.0.13 10.0.0.14 10.0.0.15"
CCC_HOST_EXTERNAL_ADDRS="203.0.113.11 203.0.113.12 203.0.113.13 203.0.113.14 203.0.113.15"
CCC_HOST_NODE_IDS="11 12 13 14 15"
...