flexvolume

FlexVolume driver on Windows is availabe from following k8s versions:

• PR: enable flexvolume on Windows node

k8s version	availabe version
v1.7	1.7.13
v1.8	1.8.6
v1.9	1.9.1

1. install FlexVolume driver on every Windows node

make a plugin directory, e.g. C:\k\volumeplugins\test~example.cmd and put driver file https://raw.githubusercontent.com/andyzhangx/Demo/master/windows/flexvolume/example.cmd under C:\k\volumeplugins\test~example.cmd

start powershell
mkdir C:\k\volumeplugins
cd C:\k\volumeplugins
mkdir test~example.cmd
cd C:\k\volumeplugins\test~example.cmd
$storageDir = $pwd
$webclient = New-Object System.Net.WebClient
$url = "https://raw.githubusercontent.com/andyzhangx/Demo/master/windows/flexvolume/example.cmd"
$file = "$storageDir\example.cmd"
$webclient.DownloadFile($url,$file)

2. specify volume-plugin-dir value in Windows kubelet service config

edit file c:\k\kubeletstart.ps1, append following config

--volume-plugin-dir=c:\k\volumeplugins

3. create a pod with FlexVolume mount on Windows

kubectl create -f https://raw.githubusercontent.com/andyzhangx/Demo/master/windows/flexvolume/aspnet-flex-example.yaml

watch the status of pod until its Status changed from Pending to Running

watch kubectl describe po aspnet-flex-example

4. enter the pod container to do validation

kubectl exec -it aspnet-flex-example -- cmd

Microsoft Windows [Version 10.0.14393]
(c) 2016 Microsoft Corporation. All rights reserved.

C:\>dir
 Volume in drive C has no label.
 Volume Serial Number is F4B3-1384

 Directory of C:\
12/07/2017  03:54 AM    <SYMLINKD>     data [\\?\ContainerMappedDirectories\8022AF84-E3B2-44AC-9BB5-9B733C92E6B8]
12/07/2017  03:54 AM    <DIR>          inetpub
11/22/2016  10:45 PM             1,894 License.txt
07/16/2016  01:18 PM    <DIR>          PerfLogs
11/03/2017  07:14 PM    <DIR>          Program Files
11/14/2017  11:48 PM    <DIR>          Program Files (x86)
11/15/2017  12:09 AM    <DIR>          RoslynCompilers
10/18/2017  04:01 PM           126,632 ServiceMonitor.exe
12/07/2017  03:54 AM    <DIR>          Users
12/07/2017  03:54 AM    <DIR>          var
12/07/2017  04:27 AM    <DIR>          Windows
               2 File(s)        128,526 bytes
               9 Dir(s)  21,129,273,344 bytes free

C:\>cd data
C:\data>dir
 Volume in drive C has no label.
 Volume Serial Number is F4B3-1384

 Directory of C:\data
12/07/2017  03:37 AM    <DIR>          .
12/07/2017  03:37 AM    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)  100,983,214,080 bytes free

Known issues

• You may get following error in the kubelet log when trying to use a flexvolume driver written by yourself:

Volume has not been added to the list of VolumesInUse

You could let flexvolume plugin return following:

echo {"status": "Success", "capabilities": {"attach": false}}

Which means your FlexVolume driver does not need Master-initiated Attach/Detach

• The main difficulty is that how to pass json parameters which contains ",, see below example

C:\tmp\test~example.cmd>.\example.cmd mount c:\var\lib\kubelet\pods\c4fd9ca4-df10-11e7-b71a-000d3a02c330\volumes\test~example2.cmd\flextest   {"kubernetes.io/fsType":"","kubernetes.io/pod.name":"aspnet-flex-example2","kubernetes.io/pod.namespace":"default","kubernetes.io/pod.uid":"c4fd9ca4-df10-11e7-b71a-000d3a02c330","kubernetes.io/pvOrVolumeName":"flextest","kubernetes.io/readwrite":"rw","kubernetes.io/serviceAccount.name":"default"}

Links

Flexvolume doc

More clear steps about flexvolume by Redhat doc: Persistent Storage Using FlexVolume Plug-ins