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CSI for S3

This is a Container Storage Interface (CSI) for S3 (or S3 compatible) storage. This can dynamically allocate buckets and mount them via a fuse mount into any container.


This is still very experimental and should not be used in any production environment. Unexpected data loss could occur depending on what mounter and S3 storage backend is being used.

Kubernetes installation


  • Kubernetes 1.13+ (CSI v1.0.0 compatibility)
  • Kubernetes has to allow privileged containers
  • Docker daemon must allow shared mounts (systemd flag MountFlags=shared)

1. Create a secret with your S3 credentials

apiVersion: v1
kind: Secret
  namespace: kube-system
  name: csi-s3-secret
  # Namespace depends on the configuration in the storageclass.yaml
  namespace: kube-system
  secretAccessKey: <YOUR_SECRET_ACCES_KEY>
  # For AWS set it to "https://s3.<region>"
  endpoint: <S3_ENDPOINT_URL>
  # If not on S3, set it to ""
  region: <S3_REGION>

The region can be empty if you are using some other S3 compatible storage.

2. Deploy the driver

cd deploy/kubernetes
kubectl create -f provisioner.yaml
kubectl create -f attacher.yaml
kubectl create -f csi-s3.yaml

3. Create the storage class

kubectl create -f examples/storageclass.yaml

4. Test the S3 driver

  1. Create a pvc using the new storage class:

    kubectl create -f examples/pvc.yaml
  2. Check if the PVC has been bound:

    $ kubectl get pvc csi-s3-pvc
    NAME         STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
    csi-s3-pvc   Bound     pvc-c5d4634f-8507-11e8-9f33-0e243832354b   5Gi        RWO            csi-s3         9s
  3. Create a test pod which mounts your volume:

    kubectl create -f examples/pod.yaml

    If the pod can start, everything should be working.

  4. Test the mount

    $ kubectl exec -ti csi-s3-test-nginx bash
    $ mount | grep fuse
    s3fs on /var/lib/www/html type fuse.s3fs (rw,nosuid,nodev,relatime,user_id=0,group_id=0,allow_other)
    $ touch /var/lib/www/html/hello_world

If something does not work as expected, check the troubleshooting section below.

Additional configuration


By default, csi-s3 will create a new bucket per volume. The bucket name will match that of the volume ID. If you want your volumes to live in a precreated bucket, you can simply specify the bucket in the storage class parameters:

kind: StorageClass
  name: csi-s3-existing-bucket
provisioner: ch.ctrox.csi.s3-driver
  mounter: rclone
  bucket: some-existing-bucket-name

If the bucket is specified, it will still be created if it does not exist on the backend. Every volume will get its own prefix within the bucket which matches the volume ID. When deleting a volume, also just the prefix will be deleted.

Using an existing bucket with custom prefix

If you have an existing bucket and with or without a prefix (subpath), you can specify to use a prefixed configuration by setting the parameters as:

kind: StorageClass
  name: csi-s3-existing-bucket
provisioner: ch.ctrox.csi.s3-driver
reclaimPolicy: Retain
  mounter: rclone
  bucket: some-existing-bucket-name
  # 'usePrefix' must be true in order to enable the prefix feature and to avoid the removal of the prefix or bucket
  usePrefix: "true"
  # 'prefix' can be empty (it will mount on the root of the bucket), an existing prefix or a new one.
  prefix: custom-prefix

Note: all volumes created with this StorageClass will always be mounted to the same bucket and path, meaning they will be identical.


As S3 is not a real file system there are some limitations to consider here. Depending on what mounter you are using, you will have different levels of POSIX compability. Also depending on what S3 storage backend you are using there are not always consistency guarantees.

The driver can be configured to use one of these mounters to mount buckets:

The mounter can be set as a parameter in the storage class. You can also create multiple storage classes for each mounter if you like.

All mounters have different strengths and weaknesses depending on your use case. Here are some characteristics which should help you choose a mounter:


  • Almost full POSIX compatibility (depends on caching mode)
  • Files can be viewed normally with any S3 client


  • Large subset of POSIX
  • Files can be viewed normally with any S3 client


  • Weak POSIX compatibility
  • Performance first
  • Files can be viewed normally with any S3 client
  • Does not support appends or random writes

s3backer (experimental*)

  • Represents a block device stored on S3
  • Allows to use a real filesystem
  • Files are not readable with other S3 clients
  • Support appends
  • Supports compression before upload (Not yet implemented in this driver)
  • Supports encryption before upload (Not yet implemented in this driver)

*s3backer is experimental at this point because volume corruption can occur pretty quickly in case of an unexpected shutdown of a Kubernetes node or CSI pod. The s3backer binary is not bundled with the normal docker image to keep that as small as possible. Use the <version>-full image tag for testing s3backer.

Fore more detailed limitations consult the documentation of the different projects.


Issues while creating PVC

Check the logs of the provisioner:

kubectl logs -l app=csi-provisioner-s3 -c csi-s3

Issues creating containers

  1. Ensure feature gate MountPropagation is not set to false
  2. Check the logs of the s3-driver:
kubectl logs -l app=csi-s3 -c csi-s3


This project can be built like any other go application.

go get -u

Build executable

make build


Currently the driver is tested by the CSI Sanity Tester. As end-to-end tests require S3 storage and a mounter like s3fs, this is best done in a docker container. A Dockerfile and the test script are in the test directory. The easiest way to run the tests is to just use the make command:

make test
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