Kubernetes flex volume

README.md

Flexvolume

Flexvolume enables users to mount vendor volumes into kubernetes. It expects vendor drivers are installed in the volume plugin path on every kubelet node.

It allows for vendors to develop their own drivers to mount volumes on nodes.

Note: Flexvolume is an alpha feature and is most likely to change in future

Prerequisites

Install the vendor driver on all nodes in the kubelet plugin path. Path for installing the plugin: /usr/libexec/kubernetes/kubelet-plugins/volume/exec/<vendor~driver>/<driver>

For example to add a 'cifs' driver, by vendor 'foo' install the driver at: /usr/libexec/kubernetes/kubelet-plugins/volume/exec/<foo~cifs>/cifs

Plugin details

Driver will be invoked with 'Init' to initalize the driver. It will be invoked with 'attach' to attach the volume and with 'detach' to detach the volume from the kubelet node. It also supports custom mounts using 'mount' and 'unmount' callouts to the driver.

Driver invocation model:

Init: <driver executable> init

Attach: <driver executable> attach <json options>

Detach: <driver executable> detach <mount device>

Mount: <driver executable> mount <target mount dir> <mount device> <json options>

Unmount: <driver executable> unmount <mount dir>

See lvm[lvm] for a quick example on how to write a simple flexvolume driver.

Example of Flexvolume

See nginx.yaml[nginx.yaml] for a quick example on how to use Flexvolume in a pod.

lvm

#!/bin/bash

# Copyright 2015 The Kubernetes Authors All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

usage() {
	err "Invalid usage. Usage: "
	err "\t$0 init"
	err "\t$0 attach <json params>"
	err "\t$0 detach <mount device>"
	err "\t$0 mount <mount dir> <mount device> <json params>"
	err "\t$0 unmount <mount dir>"
	exit 1
}

err() {
	echo -ne $* 1>&2
}

log() {
	echo -ne $* >&1
}

ismounted() {
	MOUNT=`findmnt -n ${MNTPATH} 2>/dev/null | cut -d' ' -f1`
	if [ "${MOUNT}" == "${MNTPATH}" ]; then
		echo "1"
	else
		echo "0"
	fi
}

attach() {
	VOLUMEID=$(echo $1 | jq -r '.volumeID')
	SIZE=$(echo $1 | jq -r '.size')
	VG=$(echo $1|jq -r '.volumegroup')

	DMDEV="/dev/mapper/${VG}-${VOLUMEID}"
	if [ ! -b "${DMDEV}" ]; then
		err "{\"status\": \"Failure\", \"message\": \"Volume ${VOLUMEID} does not exist\"}"
		exit 1
	fi
	log "{\"status\": \"Success\", \"device\":\"${DMDEV}\"}"
	exit 0
}

detach() {
	log "{\"status\": \"Success\"}"
	exit 0
}

domount() {
	MNTPATH=$1
	DMDEV=$2
	FSTYPE=$(echo $3|jq -r '.["kubernetes.io/fsType"]')

	if [ ! -b "${DMDEV}" ]; then
		err "{\"status\": \"Failure\", \"message\": \"${DMDEV} does not exist\"}"
		exit 1
	fi

	if [ $(ismounted) -eq 1 ] ; then
		log "{\"status\": \"Success\"}"
		exit 0
	fi

	VOLFSTYPE=`blkid -o udev ${DMDEV} 2>/dev/null|grep "ID_FS_TYPE"|cut -d"=" -f2`
	if [ "${VOLFSTYPE}" == "" ]; then
		mkfs -t ${FSTYPE} ${DMDEV}
		if [ $? -ne 0 ]; then
			err "{ \"status\": \"Failure\", \"message\": \"Failed to create fs ${FSTYPE} on device ${DMDEV}\"}"
			exit 1
		fi
	fi

	mkdir -p ${MNTPATH} &> /dev/null

	mount ${DMDEV} ${MNTPATH} &> /dev/null
	if [ $? -ne 0 ]; then
		err "{ \"status\": \"Failure\", \"message\": \"Failed to mount device ${DMDEV} at ${MNTPATH}\"}"
		exit 1
	fi
	log "{\"status\": \"Success\"}"
	exit 0
}

unmount() {
	MNTPATH=$1
	if [ $(ismounted) -eq 0 ] ; then
		log "{\"status\": \"Success\"}"
		exit 0
	fi

	umount ${MNTPATH} &> /dev/null
	if [ $? -ne 0 ]; then
		err "{ \"status\": \"Failed\", \"message\": \"Failed to unmount volume at ${MNTPATH}\"}"
		exit 1
	fi
	rmdir ${MNTPATH} &> /dev/null

	log "{\"status\": \"Success\"}"
	exit 0
}

op=$1

if [ "$op" = "init" ]; then
	log "{\"status\": \"Success\"}"
	exit 0
fi

if [ $# -lt 2 ]; then
	usage
fi

shift

case "$op" in
	attach)
		attach $*
		;;
	detach)
		detach $*
		;;
	mount)
		domount $*
		;;
	unmount)
		unmount $*
		;;
	*)
		usage
esac

exit 1

nginx.yaml

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx
    volumeMounts:
    - name: test
      mountPath: /data
    ports:
    - containerPort: 80
  volumes:
  - name: test
    flexVolume:
      driver: "kubernetes.io/lvm"
      fsType: "ext4"
      options:
        volumeID: "vol1"
        size: "1000m"
        volumegroup: "kube_vg"