Clusters
Clusters are autoscaling groups of instances backed by a load balancer. When traffic increases, new instances are added automatically. When it drops, they are removed.
1. Create a cluster
Go to Menu → Compute → Clusters → Create Cluster.
| Field | Description |
|---|---|
| Name | Cluster identifier |
| Image | Base image for all instances in the group |
| Flavor | Instance size (vCPU, RAM) |
| Min size | Minimum number of running instances |
| Max size | Maximum number of running instances |
| Backend network | Private network for internal traffic |
| SSH keypair | Key used to connect to instances |
| Port | Application port the load balancer routes to |
| DNS name | Domain name for the cluster load balancer |
| Scale-out threshold | CPU % that triggers adding an instance (e.g. 0.7 = 70%) |
| Scale-in threshold | CPU % that triggers removing an instance (e.g. 0.2 = 20%) |
| Create bastion | Add a bastion host for SSH access to the cluster |
The cluster is created as an OpenStack Heat stack. Creation takes 2–5 minutes.
2. View cluster status
From the Clusters page, each cluster shows:
- Stack name and ID
- Number of running instances
- Load balancer domain
- Current status
Click a cluster to view details including individual instance health.
3. Rolling update
A rolling update replaces the base image used by the autoscaling group without downtime. New instances spawned after the update use the new image; existing instances are replaced gradually as the group scales.
Steps:
- Create a snapshot of an instance with the updated software (Instances → Actions → Create Snapshot)
- Go to Clusters → Actions → Rolling Update
- Select the snapshot from the dropdown
- Click Start Rolling Update
Progress is shown in real time via the notification panel.
Rolling updates affect new instances spawned by autoscaling. Existing instances continue running on the old image until they are replaced by normal scale-in/scale-out cycles.
4. Delete a cluster
Go to Clusters → Actions → Delete. This removes the Heat stack, all instances in the group, and the load balancer. The operation cannot be undone.
API
| Method | Path | Description |
|---|---|---|
POST | /v1/clusters | Create a cluster |
GET | /v1/clusters | List clusters |
GET | /v1/clusters/:stackName/:stackId | Get cluster details |
PATCH | /v1/clusters/:stackName/:stackId | Update cluster (e.g. new image) |
DELETE | /v1/clusters/:stackName/:stackId | Delete a cluster |
Related
- Snapshots — create the image used for rolling updates
- Custom Domains — attach a domain to your cluster load balancer
- Clusters API — full API reference