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Enabling Controller-managed Attachment and Detachment

Overview

By default, the controller running on the cluster’s master manages volume attach and detach operations on behalf of a set of nodes, as opposed to letting them manage their own volume attach and detach operations.

Controller-managed attachment and detachment has the following benefits:

  • If a node is lost, volumes that were attached to it can be detached by the controller and reattached elsewhere.

  • Credentials for attaching and detaching do not need to be made present on every node, improving security.

Determining What Is Managing Attachment and Detachment

If a node has set the annotation volumes.kubernetes.io/controller-managed-attach-detach on itself, then its attach and detach operations are being managed by the controller. The controller will automatically inspect all nodes for this annotation and act according to whether it is present or not. Therefore, you may inspect the node for this annotation to determine if it has enabled controller-managed attach and detach.

To further ensure that the node is opting for controller-managed attachment and detachment, its logs can be searched for the following line:

Setting node annotation to enable volume controller attach/detach

If the above line is not found, the logs should instead contain:

Controller attach/detach is disabled for this node; Kubelet will attach and detach volumes

To check from the controller’s end that it is managing a particular node’s attach and detach operations, the logging level must first be set to at least 4. Then, the following line should be found:

processVolumesInUse for node <node_hostname>

For information on how to view logs and configure logging levels, see Configuring Logging Levels.

Configuring Nodes to Enable Controller-managed Attachment and Detachment

Enabling controller-managed attachment and detachment is done by configuring individual nodes to opt in and disable their own node-level attachment and detachment management. See Node Configuration Files for information on what node configuration file to edit and add the following:

kubeletArguments:
  enable-controller-attach-detach:
  - "true"

Once a node is configured, it must be restarted for the setting to take effect.