Adding Hosts to an Existing Cluster | Installation and Configuration

Overview
Adding Hosts Using the Quick Installer Tool
Adding Hosts Using the Advanced Install

Overview

Depending on how your OpenShift Container Platform cluster was installed, you can add new hosts (either nodes or masters) to your installation by using the install tool for quick installations, or by using the scaleup.yml playbook for advanced installations.

Adding Hosts Using the Quick Installer Tool

If you used the quick install tool to install your OpenShift Container Platform cluster, you can use the quick install tool to add a new node host to your existing cluster, or to reinstall the cluster entirely.

Currently, you can not use the quick installer tool to add new master hosts. You must use the advanced installation method to do so.

If you used the installer in either interactive or unattended mode, you can re-run the installation as long as you have an installation configuration file at ~/.config/openshift/installer.cfg.yml (or specify a different location with the -c option).

The recommended maximum number of nodes is 1000.

To add nodes to your installation:

Re-run the installer with the install subcommand in interactive or unattended mode:
```
$ atomic-openshift-installer [-u] [-c </path/to/file>] install
```

The installer detects your current environment and allows you to either add an additional node or re-perform a clean install:

Gathering information from hosts...
Installed environment detected.
By default the installer only adds new nodes to an installed environment.
Do you want to (1) only add additional nodes or (2) perform a clean install?:

Choose (1) and follow the on-screen instructions to complete your desired task.

Adding Hosts Using the Advanced Install

If you installed using the advanced install, you can add new hosts to your cluster by running the scaleup.yml playbook. This playbook queries the master, generates and distributes new certificates for the new hosts, then runs the configuration playbooks on the new hosts only. Before running the scaleup.yml playbook, complete all prerequisite host preparation steps.

This process is similar to re-running the installer in the quick installation method to add nodes, however you have more configuration options available when using the advanced method and when running the playbooks directly.

You must have an existing inventory file (for example, /etc/ansible/hosts) that is representative of your current cluster configuration in order to run the scaleup.yml playbook. If you previously used the atomic-openshift-installer command to run your installation, you can check ~/.config/openshift/hosts (previously located at ~/.config/openshift/.ansible/hosts) for the last inventory file that the installer generated, and use or modify that as needed as your inventory file. You must then specify the file location with -i when calling ansible-playbook later.

The recommended maximum number of nodes is 1000.

To add a host to an existing cluster:

Ensure you have the latest playbooks by updating the atomic-openshift-utils package:
```
# yum update atomic-openshift-utils
```
Edit your /etc/ansible/hosts file and add new_<host_type> to the [OSEv3:children] section:

For example, to add a new node host, add new_nodes:
```
[OSEv3:children]
masters
nodes
new_nodes
```
To add new master hosts, add new_masters.

Create a [new_<host_type>] section much like an existing section, specifying host information for any new hosts you want to add. For example, when adding a new node:

[nodes]
master[1:3].example.com
node1.example.com openshift_node_labels="{'region': 'primary', 'zone': 'east'}"
node2.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}"
infra-node1.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}"
infra-node2.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}"

[new_nodes]
node3.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}"

See Configuring Host Variables for more options.

When adding new masters, hosts added to the [new_masters] section must also be added to the [new_nodes] section. This ensures the new master host is part of the OpenShift SDN.

[masters]
master[1:2].example.com

[new_masters]
master3.example.com

[nodes]
master[1:2].example.com
node1.example.com openshift_node_labels="{'region': 'primary', 'zone': 'east'}"
node2.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}"
infra-node1.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}"
infra-node2.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}"

[new_nodes]
master3.example.com

Masters are also automatically marked as unschedulable for pod placement by the installer.

If you label a master host with the region=infra label and have no other dedicated infrastructure nodes, you must also explicitly mark the host as schedulable by adding openshift_schedulable=true to the entry. Otherwise, the registry and router pods cannot be placed anywhere.

Run the scaleup.yml playbook. If your inventory file is located somewhere other than the default of /etc/ansible/hosts, specify the location with the -i option.

For additional nodes:

# ansible-playbook [-i /path/to/file] \
    /usr/share/ansible/openshift-ansible/playbooks/byo/openshift-node/scaleup.yml

For additional masters:

# ansible-playbook [-i /path/to/file] \
    /usr/share/ansible/openshift-ansible/playbooks/byo/openshift-master/scaleup.yml

After the playbook completes successfully, verify the installation.

Finally, move any hosts you had defined in the [new_<host_type>] section into their appropriate section (but leave the [new_<host_type>] section definition itself in place) so that subsequent runs using this inventory file are aware of the nodes but do not handle them as new nodes. For example, when adding new nodes:

[nodes]
master[1:3].example.com
node1.example.com openshift_node_labels="{'region': 'primary', 'zone': 'east'}"
node2.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}"
node3.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}"
infra-node1.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}"
infra-node2.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}"

[new_nodes]