Configuring Tolerance Policies¶
Tolerations allow the scheduler to schedule pods to nodes with target taints. Tolerances work with node taints. Each node allows one or more taints. If no tolerance is configured for a pod, the scheduler will schedule the pod based on node taint policies to prevent the pod from being scheduled to an inappropriate node.
The following table shows how taint policies and tolerations affect pod running.
Taint Policy | No Taint Toleration Configured | Taint Toleration Configured |
|---|---|---|
NoExecute |
|
|
PreferNoSchedule |
| Pods can always run on this node. |
NoSchedule |
| Pods can always run on this node. |
Configuring Tolerance Policies on the Console¶
Log in to the CCE console.
When creating a workload, click Toleration in the Advanced Settings area.
Add a taint tolerance policy.
Table 1 Parameters for configuring a taint tolerance policy¶ Parameter
Description
Taint key
Key of a node taint
Operator
Equal: Exact match for the specified taint key (mandatory) and taint value. If the taint value is left blank, all taints with the key the same as the specified taint key will be matched.
Exists: matches only the nodes with the specified taint key. In this case, the taint value cannot be specified. If the taint key is left blank, all taints will be tolerated.
Taint value
Taint value specified if the operator is set to Equal.
Taint Policy
All: All taint policies are matched.
NoSchedule: Only the NoSchedule taint is matched.
PreferNoSchedule: Only the PreferNoSchedule taint is matched.
NoExecute: Only the NoExecute taint is matched.
Toleration Time Window
tolerationSeconds, which is configurable only when Taint Policy is set to NoExecute.
Within the tolerance time window, pods still run on the node with taints. After the time expires, the pods will be evicted.
Default Tolerance Policy¶
Kubernetes automatically adds tolerances for the node.kubernetes.io/not-ready and node.kubernetes.io/unreachable taints to pods, and sets the tolerance time window (tolerationSeconds) to 300s. These default tolerance policies indicate that when either of the preceding taint is added to the node where pods are running, the pods can still run on the node for 5 minutes.
Note
When a DaemonSet pod is created, no tolerance time window will be specified for the tolerances automatically added for the preceding taints. When either of the preceding taints is added to the node where the DaemonSet pod is running, the DaemonSet pod will never be evicted.
tolerations:
- key: node.kubernetes.io/not-ready
operator: Exists
effect: NoExecute
tolerationSeconds: 300
- key: node.kubernetes.io/unreachable
operator: Exists
effect: NoExecute
tolerationSeconds: 300