# Configuring container clusters for high availability


## Overview

In order to achieve high availability for your application, you need multiple redundancy for both master and worker nodes. This means at least **three master nodes** and enough worker nodes to comfortably run your entire application at no more than 75% utilisation. If you’re not sure of how Kubernetes defines nodes, please [read our guide](/:product/:version?/cloud-66-101/concepts-and-terminology#nodes-masters--workers) on the subject before getting started.

Applications running Kubernetes v1.12 or lower do not support the multi-master feature on Cloud 66. If you have deployed an application via Cloud 66 before March 2019, you will need to **redeploy your application "with upgrades" and choose to perform a Kubernetes upgrade** (note that this will incur significant downtime as your cluster will be recreated). All applications deployed after **March 2019** on version v1.13 and above automatically support multi-master clusters.

## Adding nodes to an application

To add nodes to an existing application:

1. Open the application page from your [Dashboard](https://app.cloud66.com/dashboard)
2. Click *Application* in the left-hand nav
3. Click *Servers* in the sub nav
4. Click *+ Scale up* (top right of the main panel)
5. Choose whether the new node(s) will be Master(s) or a Worker(s)
6. Choose the server size for the new node(s)
7. Choose how many new nodes to add
8. Click *Add Server* to provision your new node(s)

You can simultaneously add multiple nodes to a cluster this way, and that each of these will provision a new server with your cloud provider.