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Node Groups

Node Groups

Node groups can be used to create heterogeneous clusters.

This functionality is only supported for Kubernetes clusters.

Create a new node group

When a cluster is created it already has two node groups, default-master and default-worker.

$ openstack coe cluster list
+--------------------------------------+------+-----------+------------+--------------+-----------------+---------------+
| uuid                                 | name | keypair   | node_count | master_count | status          | health_status |
+--------------------------------------+------+-----------+------------+--------------+-----------------+---------------+
| ef7011bb-d404-4198-a145-e8808204cde3 | kube | default   |          1 |            1 | CREATE_COMPLETE | HEALTHY       |
+--------------------------------------+------+-----------+------------+--------------+-----------------+---------------+

$ openstack coe nodegroup list kube
+--------------------------------------+----------------+-----------+----------------------------------------+------------+-----------------+--------+
| uuid                                 | name           | flavor_id | image_id                               | node_count | status          | role   |
+--------------------------------------+----------------+-----------+----------------------------------------+------------+-----------------+--------+
| adc3ecfa-d11e-4da7-8c44-4092ea9dddd9 | default-master | m1.small  | Fedora-AtomicHost-29-20190820.0.x86_64 |          1 | CREATE_COMPLETE | master |
| 186e131f-8103-4285-a900-eb0dcf18a670 | default-worker | m1.small  | Fedora-AtomicHost-29-20190820.0.x86_64 |          1 | CREATE_COMPLETE | worker |
+--------------------------------------+----------------+-----------+----------------------------------------+------------+-----------------+--------+

The default-worker node group cannot be removed or reconfigured, so the initial cluster configuration should take this into account.

To add a new node group, use openstack coe nodegroup create. The only required parameters are the cluster ID and the name for the new node group, but several extra options are available.

Roles

Roles can be used to show the purpose of a node group, and multiple node groups can be given the same role if they share a common purpose.

$ openstack coe nodegroup create kube test-ng --node-count 1 --role test

When listing node groups, the role may be used as a filter:

$ openstack coe nodegroup list kube --role test
+--------------------------------------+---------+-----------+----------------------------------------+------------+--------------------+------+
| uuid                                 | name    | flavor_id | image_id                               | node_count | status             | role |
+--------------------------------------+---------+-----------+----------------------------------------+------------+--------------------+------+
| b4ab1fcb-f23a-4d1f-b583-d699a2f1e2d7 | test-ng | m1.small  | Fedora-AtomicHost-29-20190820.0.x86_64 |          1 | CREATE_IN_PROGRESS | test |
+--------------------------------------+---------+-----------+----------------------------------------+------------+--------------------+------+

The node group role will default to "worker" if unset, and the only reserved role is "master".

Role information is available within Kubernetes as labels on the nodes.

$ kubectl get nodes -L magnum.openstack.org/role
NAME                               STATUS   AGE    VERSION   ROLE
kube-r6cyw4bjb4lr-master-0         Ready    5d5h   v1.16.0   master
kube-r6cyw4bjb4lr-node-0           Ready    5d5h   v1.16.0   worker
kube-test-ng-lg7bkvjgus4y-node-0   Ready    61s    v1.16.0   test

This information can be used for scheduling, using a node selector.

nodeSelector:
  magnum.openstack.org/role: test

The label magnum.openstack.org/nodegroup is also available for selecting a specific node group.

Flavor

The node group flavor will default to the minion flavor given when creating the cluster, but can be changed for each new node group.

$ openstack coe nodegroup create ef7011bb-d404-4198-a145-e8808204cde3 large-ng --flavor m2.large

This can be used if you require nodes of different sizes in the same cluster, or to switch from one flavor to another by creating a new node group and deleting the old one.

Availability zone

To create clusters which span more than one availability zone, multiple node groups must be used. The availability zone is passed as a label to the node group.

$ openstack coe nodegroup create kube zone-a --merge-labels --labels availability_zone=cern-geneva-a ...
$ openstack coe nodegroup create kube zone-b --merge-labels --labels availability_zone=cern-geneva-b ...
$ openstack coe nodegroup create kube zone-c --merge-labels --labels availability_zone=cern-geneva-c ...

Zone information is available within the cluster as the label topology.kubernetes.io/zone on each node, or as the now deprecated label failure-domain.beta.kubernetes.io/zone.

Note: When you override the availability zone, like any other label, you need to pass --merge-labels at creation.

From Kubernetes 1.16 and onwards it is possible to balance the number of pods in a deployment across availability zones (or any other label).

Resize

Resizing a node group is done with the same API as resizing a cluster, but the --nodegroup parameter must be used.

$ openstack coe cluster resize kube --nodegroup default-worker 2
Request to resize cluster ef7011bb-d404-4198-a145-e8808204cde3 has been accepted.

As usual the --nodes-to-remove parameter may be used to remove specific nodes when decreasing the size of the node group.

Delete

Any node group except the default master and worker node groups can be deleted, by specifying the cluster and nodegroup name or ID.

$ openstack coe nodegroup delete ef7011bb-d404-4198-a145-e8808204cde3 test-ng

Restrictions

Cluster autoscaler

Autoscaling node groups is only possible when using the cluster autoscaler on Kubernetes v1.19 or later. For clusters running the cluster autoscaler on earlier versions, no extra node groups should be added to the cluster.

There is more information for autoscaling node groups in the autoscaler documentation.


Last update: November 5, 2020