Failed to find device path /dev/xvdac. no device path for device \"/dev/xvdac\" volume \"vol-02d38d88d79844a04\" found

[balusarakesh]

/kind bug

What happened?
Restarted the pod and now the EBS volume is not getting mounted on the node. As you can see from the screenshot that device name /dev/xvdac does not exist and the ebs-csi-node pod is stuck unable to mount the volume.

What you expected to happen?
A pod restart should not break EBS volume mount

How to reproduce it (as minimally and precisely as possible)?
Not really sure

Anything else we need to know?:
E0612 21:49:29.699613 1 driver.go:107] "GRPC error" err="rpc error: code = Internal desc = Failed to find device path /dev/xvdac. no device path for device \"/dev/xvdac\" volume \"vol-02d38d88d79844a04\" found"

Environment

• Kubernetes version (use kubectl version):

Client Version: v1.28.9
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: v1.28.9-eks-036c24b

• Driver version: v1.30.0
  

[balusarakesh]

for anyone looking for a workaround, manually mount the volume onto the same node and use a different devicepath, that seems to have fixed the problem

[ConnorJC3]

Hi, if you can find a way to reproduce this issue please let us know, but this issue as written doesn't provide enough information to diagnose the issue. Restarting the pod using a volume does not normally prevent the volume from attaching.

Note that this issue may occur if the volume is manually mounted/unmounted. The EBS CSI Driver does not support and strongly discourages manual mounting of volumes. If this issue occurs in the future, we recommend deleting (and allowing a ReplicaSet to recreate) the broken pod to reschedule it onto another node.

[balusarakesh]

@ConnorJC3

• unfortunately this happens randomly and there is no way to reproduce this error with 100% certainity
• the volume was never mounted manually (it was only mounted manually when the above error was observed)
• this is a statefulset so no ReplicaSet is involved here
• the issue seems to that the CSI driver is looking for a device id that does not exist for the EBS volume
• the issue only happens for like 1or 2 pods in a cluster with hundreds of pods
• I do understand that without a way to reproduce this error it's hard to fix but the error message should be adequate enough to debug this , I think the EBS CSI driver should pick device ids that actually EXIST on the volume

[AndrewSirenko]

@balusarakesh this might be a red herring, but next time you run into this issue can you confirm that the mount permissions on the /dev directory are read/write (rw) NOT read only (ro)?

We have seen similar symptoms on another customer's cluster where some other process was making it read-only, which means the device name would not show up in /dev after volume is attached AND therefore customer would not be able to mount.

When running sudo mount from node you should see something like devtmpfs on /dev type devtmpfs (rw ...) NOT devtmpfs on /dev type devtmpfs (ro ...).

Manually running sudo mount -o remount,rw /dev would reset the mount with rw permissions.

but the error message should be adequate enough to debug this

What error message would be more helpful here? I believe Failed to find device path /dev/xvdac. no device path for device \"/dev/xvdac\" volume \"vol-02d38d88d79844a04\" found" summarizes the root cause of why EBS CSI Node service cannot mount (it cannot find the device). Perhaps we can add the full path to the volume as well instead of just volume-id, or an instruction to confirm that these paths exist? But I'm afraid that more prescriptive advice might mislead users in other edge-cases.

[balusarakesh]

@AndrewSirenko I'll try to check the permissions next time it happens (thanks for the commands)

as you can see from the AWS screenshot, the device id does not exist on the volume for the given instance, doesn't that mean the ebs-csi-driver should pick a different device id that is available?

I manually mounted the volume on the node with a different device id that was available and it worked so it seems like the aws-ebs-csi driver is picking non-existent device ids

[AndrewSirenko]

For context of anyone who stumbles on this issue, it is important to remember that EBS CSI Driver is split into two components, the EBS CSI Controller Pod (responsible for talking to EC2 to make sure volumes are created and attached to the right node) and the EBS CSI Node pod (running on each node, responsible for formatting and mounting already attached volume to proper node mount-point and then pod mount-point).

as you can see from the AWS screenshot, the device id does not exist on the volume for the given instance, doesn't that mean the ebs-csi-driver should pick a different device id that is available?

@balusarakesh By the time the mount operation is happening (NodeStageVolume, see csi-spec), a volume has already been attached by controller pod to an already chosen device name. If the volume is not attached at the time of the mount operation happening, or the EBS CSI Node pod checks the wrong device path, something is very wrong (because the Kubernetes state of the world and EC2 state of the world are out of sync)

This device name can be seen on the volumeattachment object in Kubernetes, or from EC2 API if you manually query ec2 describe-volumes --volume-id <your-vol-id>

See below for an example of attached volume with device /dev/xvdaa:

{
    "Volumes": [
        {
            "Attachments": [
                {
                    "AttachTime": "2024-06-14T19:25:46+00:00",
                    "Device": "/dev/xvdaa",
                    "InstanceId": "i-0ea137a9b7ee4684a",
                    "State": "attached",
                    "VolumeId": "vol-01da7da10d37d277b",
                    "DeleteOnTermination": false
                }
            ],
...
            "State": "in-use",
            "VolumeId": "vol-01da7da10d37d277b",

The EBS CSI Node pod does not choose the device name at the time of mounting. If the csi node service fails to find that path, as a backup the ebs csi node service tries to find the device via the volume ID under /dev/disk/by-id/. The error you are seeing shows that for some reason the volume cannot be seen by the node pod at the already-chosen device name (in this case /dev/xvdac) AND the typical NVME Volume ID lookup /dev/disk/by-id/vol-xyz.

---

Next time you run into this issue can you:

1. Provide proof relevant EBS Volume is attached to underlying EC2 instance (via EC2 DescribeVolumes)
2. Post deviceName found when calling EC2 DescribeVolumes, and the device on the volumeattachment object (volumeattachment object will have a field with pv-name)
3. Provide logs of CSI Node pod with loglevel=7
4. Try to manually ssh into node (if possible) and check for /dev/ for existence of device name AND /dev/disk/by-id/ for existence of path with volume's id? If you can see those paths while ssh'd then the EBS CSI node pod may have insufficient permissions. If you can't see the paths there then something is wrong with the volume attachment.

Some customer has allegedly observed that if /dev is read-only, then even if an EC2 AttachVolume call succeeds and volume is in state attached, the path to device might still not exist.

---

Hope some of ^^ was helpful. I do not know why manually mounting a volume with a dif available device id would work, unless step 2 of the above instructions has a mismatch between what EC2 DescribeVolumes says and what volumeattachment object says is device path.

[balusarakesh]

The above message is super helpful, thank you very much for taking the time and writing it.
I'll follow the steps if this happens next and time and let you know

I'll leave it up to you to close or keep the issue open

• Thanks again