topologySpreadConstraints parameter

Use the topologySpreadConstraints parameter to define a list of Topology Spread Constraints definitions to spread pods evenly to the nodes.

Defining this parameter helps control how pods are spread across your cluster among failure domains such as regions, zones, nodes, and other user-defined topology domains. If server configurations are defined, the Operator pulls from a predefined set of constraints and integrates them into the pod specification of the managed workload.

The following YAML snippet is a sample schema of topologySpreadConstraints:

spec:
  topologySpreadConstraints:
    - name: constraint1
      maxSkew: 1
      topologyKey: topology.kubernetes.io/zone
      whenUnsatisfiable: DoNotSchedule
      labelSelector:
        matchLabels:
          app: sip
      matchLabelKeys:
        - type
      minDomains: 3

    - name: constraint2
      maxSkew: 2
      topologyKey: kubernetes.io/hostname
      whenUnsatisfiable: ScheduleAnyway
The following table explains the properties applicable for the topologySpreadConstraints parameter of SIPEnvironment. For more information, see Pod Topology Spread Constraints.
Table 1. Properties of topologySpreadConstraints
Property Default value Value type Required Description
name   string Yes Specify the name of the Topology Spread Constraint.
maxSkew   integer Yes Specify the degree to which pods might be unevenly distributed. This is a mandatory property and its value must be greater than zero.
minDomains   integer No Specify the minimum number of eligible domains.
topologyKey   string Yes Specify the key of node labels.
whenUnsatisfiable   string Yes Specify this property to determine how a pod is handled if it does not satisfy the spread constraint.
labelSelector   string No Specify this property to find matching pods.
matchLabelKeys   string No Specify the list of pod label keys to select the pods over which spreading will be calculated.
nodeAffinityPolicy   string No Specify this property to determine how nodeAffinity or nodeSelector of a pod are treated when calculating the pod topology spread skew. Allowed values are Honor or Ignore.
nodeTaintsPolicy   string No Specify this property to determine how node taints are treated when calculating the pod topology spread skew. Allowed values are Honor or Ignore.

Examples to call Topology Spread Constraints from servers

Example 1

The following example demonstrates how to define topologySpreadConstraints and use it for all the pods from ApiSupplies and ApiDemands to spread evenly and independently, by using the matchLabelKeys.

  1. Define topologySpreadConstraints in SIPEnvironment custom resource.
    
spec:
  topologySpreadConstraints:
    - name: constraint1
      maxSkew: 1
      topologyKey: topology.kubernetes.io/zone
      whenUnsatisfiable: ScheduleAnyway
      labelSelector:
        matchLabels:
          app: sip
       matchLabelKeys: type
  2. From the individual server or service group custom resource, call the topologies that are defined in step 1.
     appServers:
    - active: true
      names:
        - ApiSupplies
      podLabels:
          app: sip
          type: appserver1
      topology:
        - [constraint1]
    - active: true
      names:
        - ApiDemands
      podLabels:
          app: sip
          type: appserver2
      topology:
        - [constraint1]

Example 2

The following example demonstrates how to define topologySpreadConstraints and use it for all the pods from ApiSupplies and ApiDemands to spread together.

  1. Define topologySpreadConstraints in SIPEnvironment custom resource.
    spec:
  topologySpreadConstraints:
    - name: constraint1
      maxSkew: 1
      topologyKey: topology.kubernetes.io/zone
      whenUnsatisfiable: ScheduleAnyway
      labelSelector:
        matchLabels:
          app: sip
  2. From the individual server or service group custom resource, call the topologies that are defined in step 1.
    appServers:
    - active: true
      names:
        - ApiSupplies
      podLabels:
          app: sip
          type: appserver1
      topology:
        - [constraint1]
    - active: true
      names:
        - ApiDemands
      podLabels:
          app: sip
          type: appserver2
      topology:
        - [constraint1]