Draining a Node¶
Scenario¶
After you enable the nodal drainage function on the console, the system sets the node to be non-schedulable and securely evicts all pods that comply with Nodal Drainage Rules on the node. Subsequent new pods will not be scheduled to the node.
When a node is faulty, this function helps you quickly isolate the faulty node. The evicted pods will be transferred from the workload controller to another node that can be scheduled properly.
Constraints¶
Only clusters of the following versions support the nodal drainage function:
v1.21: v1.21.10-r0 or later
v1.23: v1.23.8-r0 or later
v1.25: v1.25.3-r0 or later
v1.25 or later
To use the nodal drainage function, an IAM user must have at least one of the following permissions. For details, see Namespace Permissions (Kubernetes RBAC-based).
cluster-admin (administrator): read and write permissions on all resources in all namespaces.
drainage-editor: drain a node.
drainage-viewer: view the nodal drainage status but cannot drain a node.
If a disruption budget is not specify for the workload, the workload function may be unavailable during pod rescheduling.
Nodal Drainage Rules¶
The nodal drainage function securely evicts pods on a node. However, for pods that meet the following filtering criteria, the system performs the corresponding operations:
Filter Criterion | Forced Drainage Enabled | Forced Drainage Disabled |
|---|---|---|
The status.phase field of the pod is Succeeded or Failed. | Deletion | Deletion |
The pod is not managed by the workload controller. | Deletion | Drainage cancellation |
The pod is managed by DaemonSet. | None | Drainage cancellation |
A volume of the emptyDir type is mounted to the pod. | Eviction | Drainage cancellation |
The pod is a static pod directly managed by kubelet | None | None |
Note
The following operations may be performed on pods during nodal drainage:
Deletion: The pod is deleted from the current node and will not be scheduled to other nodes.
Eviction: The pod is deleted from the current node and rescheduled to another node.
None: The pod will not be evicted or deleted.
Drainage cancellation: If a pod on a node cancels drainage, the drainage process of the node is terminated and no pod is evicted or deleted.
Procedure¶
Log in to the CCE console and click the cluster name to access the cluster console.
In the navigation pane, choose Nodes. On the displayed page, click the Nodes tab.
Locate the target node and choose More > Nodal Drainage in the Operation column.
In the Nodal Drainage window displayed, set parameters.
Timeout (s): The drainage task automatically fails after the preset timeout period. The value 0 indicates that the timeout period is not set.
Forced Drainage: If this function is enabled, pods managed by DaemonSet will be ignored, and pods with emptyDir volumes and pods not managed by controllers will be deleted. For details, see Nodal Drainage Rules.
Click OK and wait until the nodal drainage is complete.