Labels and annotations

IBM Storage Scale container native assigns labels to worker nodes.

Designation labels

IBM Storage Scale container native automatically assigns designations to some worker nodes. You do not need to explicitly designate the worker nodes but if it is required then it can be done by using node labels.

The following mechanisms are supported to designate IBM Storage Scale container native nodes:

Automatic (Recommended) - Allows the Operator to designate the nodes automatically.
Manual (Optional) - Allows administrators to have more control of the placement of IBM Storage Scale node designations (like the quorum designation) to pods on specific worker nodes.

Manual labeling requires insight about IBM Storage Scale and must not be used by unexperienced administrators.

Automatic

If the user does not label any nodes as quorum nodes, the Operator automatically applies quorum annotations to a subset of the nodes in the cluster. The number of nodes to be annotated depends on the number of nodes in the cluster:

If the number of nodes in the cluster definition is less than 4, all nodes are designated as quorum nodes.
If the number of nodes in the cluster definition is between 4 and 9 inclusive, 3 nodes are designated as quorum nodes.
If the number of nodes in the cluster definition is between 10 and 18 inclusive, 5 nodes are designated as quorum nodes.
If the number of nodes in the cluster definition is greater than 18, 7 nodes are designated as quorum nodes.

Kubernetes zones are considered whether they are configured in the Red Hat OpenShift cluster. The operator selects quorum nodes across all zones. For example, if 3 zones and 3 quorum nodes are to be designated as quorum nodes, then one node of each zone is designated as quorum node. For more information, see Kubernetes zones.

The automatic node designation works at initial cluster creation time only. When the cluster is created, the operator does not change node designations automatically (for example if nodes are added to the cluster). If node designations must be changed on an existing cluster, the Manual steps can be done, even if Automatic mode was used at cluster creation time.

Manual

Supported designation label values are quorum and manager. The nodes designated as quorum nodes also automatically assume the role of manager. If sufficient quorum nodes are designated, unlabeled nodes become client nodes within the cluster.

IBM Storage Scale quorum designation

For more information about IBM Storage Scale quorum designation, see Quorum in IBM Storage Scale documentation. It is mandatory to configure an odd number of nodes, with 3, 5, or 7 nodes are the typical numbers used.

IBM Storage Scale manager designation

For more information about IBM Storage Scale manager designation, see Special management functions in IBM Storage Scale documentation.

Node labeling

To see the list of nodes in your cluster, enter the oc get nodes command:

# oc get nodes
NAME                           STATUS   ROLES    AGE   VERSION
master0.example.com   Ready    master   50d   v1.16.2
worker0.example.com   Ready    worker   50d   v1.16.2
worker1.example.com   Ready    worker   50d   v1.16.2
worker2.example.com   Ready    worker   50d   v1.16.2

The following labels can be applied to nodes in the Red Hat OpenShift cluster to dictate how the pods are deployed on the nodes that are designated:

scale.spectrum.ibm.com/designation=quorum
scale.spectrum.ibm.com/designation=manager

To apply a label to a node, enter the oc label node <node name> scale.spectrum.ibm.com/designation=<designation> command as follows:

oc label node worker0.example.com scale.spectrum.ibm.com/designation=quorum

To verify that the label was applied to the node, enter the oc describe node <node name> command as follows:

# oc describe node worker0.example.com
Name:               worker0.example.com
...
Labels:             ...
                    ...
                    scale.spectrum.ibm.com/designation=quorum
...

To remove a label from a node, enter the following command:

oc label node <node name> scale.spectrum.ibm.com/designation-

Quorum node designations can be changed on the IBM Storage Scale container native cluster by manually applying or removing node labels. Manual labeling requires insight about IBM Storage Scale and must not be done by unexperienced administrators.