Node scaling for etcd
In general, clusters must have 3 control plane nodes. However, if your cluster is installed on a bare metal platform, it can have up to 5 control plane nodes. If your bare-metal cluster has fewer than 5 control plane nodes, you can scale up the cluster as a postinstallation task.
For example, to scale from 3 to 4 control plane nodes after installation, you can add a host and install it as a control plane node. Then, the etcd Operator scales accordingly to account for the additional control plane node.
Scaling a cluster to 4 or 5 control plane nodes is available only on bare metal platforms.
For more information about how to scale control plane nodes by using the Assisted Installer, see "Adding hosts" and "Replacing a control plane node in a healthy cluster".
|
|
While adding control plane nodes can increase reliability and availability, it can decrease throughput and increase latency, affecting performance. |
The following table shows failure tolerance for clusters of different sizes:
| Cluster size | Majority | Failure tolerance |
|---|---|---|
1 node |
1 |
0 |
3 nodes |
2 |
1 |
4 nodes |
3 |
1 |
5 nodes |
3 |
2 |
For more information about recovering from quorum loss, see "Restoring to an earlier cluster state".