Bug 1315995 - Creating pods on OSE v3.1.1.911 with awsElasticBlockStore only assigns devices /dev/xvdb - /dev/xvdp to openshift node
Creating pods on OSE v3.1.1.911 with awsElasticBlockStore only assigns device...
Product: OpenShift Origin
Classification: Red Hat
Component: Storage (Show other bugs)
Unspecified Unspecified
urgent Severity low
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Assigned To: Jan Safranek
Jianwei Hou
Depends On:
Blocks: 1318974
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Reported: 2016-03-09 03:36 EST by Elvir Kuric
Modified: 2017-03-22 05:12 EDT (History)
8 users (show)

See Also:
Fixed In Version: atomic-openshift-3.5.0
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
: 1318974 (view as bug list)
Last Closed: 2017-03-22 05:12:21 EDT
Type: Bug
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Elvir Kuric 2016-03-09 03:36:32 EST
Description of problem:

When creating Openshift pods with AWS EBS plugin it is possible only to attach /dev/xvdb - /dev/xvdp to openshift node and thus only to start number of pods which is equal to number of allocated EBS devices ( /dev/xvdb - /dev/xvdp ) 
Openshift pods uses AWS EBS as persistent storage 

Version-Release number of selected component (if applicable):

# Openshift packages installed 

# rpm -qa | grep atomic-opensh
root@ip-172-31-7-106: ~ # uname -a 
Linux ip-172-31-7-106.us-west-2.compute.internal 3.10.0-327.el7.x86_64 #1 SMP Thu Oct 29 17:29:29 EDT 2015 x86_64 x86_64 x86_64 GNU/Linux

How reproducible:

On functional Openshift environment ( I tested with two Openshift nodes ) with above packages, run 

# python create_ebs_pod.py --volumesize=1 --image=r7perffio --tagprefix=openshift_test --minpod=1 --maxpod=44 --pvfile=pv.json --pvcfile=pvc.json --podfile=pod.json

This will create 43 pods with one 1 GB  EBS device attached to each of them, and approximatelly 20 pods an ose node should get.  
However, not all 20 pods will start, but only up to exhaustion of devices ( /dev/xvda - /dev/xvdb ). 



can be found at : https://github.com/ekuric/openshift/tree/master/_aws 

Steps to Reproduce:
Please see step above 

Actual results:

Last device attached to amazon instance ( acting as openshift node ) in tests when awsElasticBlockStore plugin was used was /dev/xvdp
what means that devices from /dev/xvdb - /dev/xvdp were available for pods to use as persistent storage. After this, no more pods were possible to start.

Expected results:

to be albe to attach more EBS devices to amazon instance when using awsElasticBlockStore plugin  - and be able to start more Openshift pods 

Additional info:

In logs is stated below [1] 

Amazon : 

WS cloud provider says:

// See:
devices := []mountDevice{}
for c := 'f'; c <= 'p'; c++ {
	devices = append(devices, mountDevice(fmt.Sprintf("%c", c)))

pod file used : https://github.com/ekuric/openshift/blob/master/_aws/pod.json
pv file used: https://github.com/ekuric/openshift/blob/master/_aws/pv.json
pvcfile used : https://github.com/ekuric/openshift/blob/master/_aws/pvc.json 

Mar  8 08:24:23 ip-172-31-7-105 atomic-openshift-node: E0308 08:24:23.508726   12979 pod_workers.go:138] Error syncing pod 8f3bf98c-e529-11e5-b35d-028bb7d6e433, skipping: Could not attach EBS Disk "vol-9652ec60". Timeout waiting for mount paths to be created.
Mar  8 08:24:23 ip-172-31-7-105 atomic-openshift-node: W0308 08:24:23.656873   12979 aws_util.go:167] Retrying attach for EBS Disk "vol-9b53ed6d" (retry count=7).
Mar  8 08:24:23 ip-172-31-7-105 atomic-openshift-node: W0308 08:24:23.770064   12979 aws.go:950] Unexpected EBS DeviceName: "/dev/sda1"
Mar  8 08:24:23 ip-172-31-7-105 atomic-openshift-node: W0308 08:24:23.770114   12979 aws.go:983] Could not assign a mount device (all in use?).  mappings=map[b:vol-6936fc9f f:vol-b954ea4f j:vol-4154eab7 l:vol-1b54eaed m:vol-9855eb6e p:vol-4155ebb7 a1:vol-a236fc54 g:vol-c654ea30 h:vol-2754ead1 i:vol-6e54ea98 k:vol-7a54ea8c n:vol-2c55ebda o:vol-ad55eb5b], valid=[f g h i j k l m n
Comment 1 Jan Safranek 2016-03-09 10:05:50 EST
This is the root cause:

Kubernetes uses only devices /dev/xvd[f-p] or /dev/sd[f-p], as suggested by

    "Recommended for EBS Volumes: ... /dev/sd[f-p]"

This leaves us with 11 EBS volumes, which is quite few. IMO we could use more, up to 40 volumes supported by Amazon.

As related bug, when Kubernetes runs out of device names, 'kubectl describe pod' shows cryptic error:
'Value (/dev/xvd) for parameter device is invalid. /dev/xvd is not a valid EBS device name.'
IMO we should print something like 'Too many devices attached, only 11 devices are supported by AWS.'
Note to self: look at https://github.com/kubernetes/kubernetes/blob/master/pkg/cloudprovider/providers/aws/aws.go#L1054 and try to return an error here.
Comment 2 Jan Safranek 2016-03-14 11:43:08 EDT
Created PR https://github.com/kubernetes/kubernetes/pull/22942 and waiting for upstream feedback.
Comment 3 Jan Safranek 2016-03-16 08:43:36 EDT
The first part, raising the limit to 39 has been merged to Kubernetes 1.2. Admins can adjust the limit by setting env. variable "KUBE_MAX_PD_VOLS" in scheduler process (openshift-master), however kubelet will refuse to attach more that 39 volumes anyway. 'oc describe pod' will show clear message that too many volumes are attached and a pod can't be started.


The second part, allowing kubelet to attach more than 39 volumes, is still open and I'm working on it. Tracked here: https://github.com/kubernetes/kubernetes/issues/22994
Comment 4 Jan Safranek 2016-03-18 13:50:16 EDT
sorry, wrong bug, moving back to assigned
Comment 6 Jan Safranek 2016-03-20 10:44:43 EDT
Experimental fix for the second part: https://github.com/kubernetes/kubernetes/pull/23254

Waiting for upstream feedback.
Comment 7 Bradley Childs 2016-05-23 23:37:04 EDT
Fix merged upstream. Target this for OSE 3.2.1 ?
Comment 8 Jan Safranek 2016-06-14 09:29:39 EDT
I'm marking it as 'POST', i.e. fixed in Kubernetes and waiting for OpenShift rebase.
Comment 9 Jan Safranek 2017-03-22 05:12:21 EDT
AWS changed in the meantime and now it actually enforces devices to be named according to https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/block-device-mapping-concepts.html

Only devices /dev/xvd[b-c][a-z] are usable now. This was merged into Kubernetes as https://github.com/kubernetes/kubernetes/pull/41455 and into OpenShift as bug #1422531 (see the bug for releases where it was fixed).

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