external-resizer

CSI Resizer

The CSI external-resizer is a sidecar container that watches the Kubernetes API server for PersistentVolumeClaim updates and triggers ControllerExpandVolume operations against a CSI endpoint if user requested more storage on PersistentVolumeClaim object.

Overview

A storage provider that allows volume expansion after creation, may choose to implement volume expansion either via a control-plane CSI RPC call or via node CSI RPC call or both as a two step process. The external-resizer is an external-controller that watches Kubernetes API server for PersistentVolumeClaim modifications and triggers CSI calls for control-plane volume-expansion. More details can be found on - CSI Volume expansion

Compatibility

This information reflects the head of this branch.

Feature status

Currently all CSI volume expansion features are supported as Beta features by external-resizer.

Usage

It is necessary to create a new service account and give it enough privileges to run the external-resizer, see deploy/kubernetes/rbac.yaml. The resizer is then deployed as single Deployment as illustrated below:

kubectl create deploy/kubernetes/deployment.yaml

The external-resizer may run in the same pod with other external CSI controllers such as the external-attacher, external-snapshotter and/or external-provisioner.

Note that the external-resizer does not scale with more replicas. Only one external-resizer is elected as leader and running. The others are waiting for the leader to die. They re-elect a new active leader in ~15 seconds after death of the old leader.

Command line options

Recommended optional arguments

• --csi-address <path to CSI socket>: This is the path to the CSI driver socket inside the pod that the external-resizer container will use to issue CSI operations (/run/csi/socket is used by default).

• --leader-election: Enables leader election. This is mandatory when there are multiple replicas of the same external-resizer running for one CSI driver. Only one of them may be active (=leader). A new leader will be re-elected when current leader dies or becomes unresponsive for ~15 seconds.

• --leader-election-namespace: Namespace where the leader election resource lives. Defaults to the pod namespace if not set.

• ---csiTimeout <duration>: Timeout of all calls to CSI driver. It should be set to value that accommodates majority of ControllerExpandVolume calls. 15 seconds is used by default.

• --workers <num>: Number of simultaneously running ControllerExpandVolume operations. Default value is 10.

Other recognized arguments

• --kubeconfig <path>: Path to Kubernetes client configuration that the external-resizer uses to connect to Kubernetes API server. When omitted, default token provided by Kubernetes will be used. This option is useful only when the external-resizer does not run as a Kubernetes pod, e.g. for debugging. Either this or --master needs to be set if the external-resizer is being run out of cluster.

• --master <url>: Master URL to build a client config from. When omitted, default token provided by Kubernetes will be used. This option is useful only when the external-resizer does not run as a Kubernetes pod, e.g. for debugging. Either this or --kubeconfig needs to be set if the external-resizer is being run out of cluster.

• --version: Prints current external-resizer version and quits.

• All glog / klog arguments are supported, such as -v <log level> or -alsologtostderr.

Community, discussion, contribution, and support

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