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Chapter 2. Configuring persistent storage

2.1. Persistent Storage Using AWS Elastic Block Store

OpenShift Container Platform supports AWS Elastic Block Store volumes (EBS). You can provision your OpenShift Container Platform cluster with persistent storage using AWS EC2. Some familiarity with Kubernetes and AWS is assumed.

The Kubernetes persistent volume framework allows administrators to provision a cluster with persistent storage and gives users a way to request those resources without having any knowledge of the underlying infrastructure. AWS Elastic Block Store volumes can be provisioned dynamically. Persistent volumes are not bound to a single project or namespace; they can be shared across the OpenShift Container Platform cluster. Persistent volume claims are specific to a project or namespace and can be requested by users.

Important

High-availability of storage in the infrastructure is left to the underlying storage provider.

Additional References

Amazon EC2

2.1.1. Creating the EBS Storage Class

StorageClasses are used to differentiate and delineate storage levels and usages. By defining a storage class, users can obtain dynamically provisioned persistent volumes.

Procedure

In the OpenShift Container Platform console, click Storage Storage Classes.
In the storage class overview, click Create Storage Class.
Define the desired options on the page that appears.
1. Enter a name to reference the storage class.
2. Enter an optional description.
3. Select the reclaim policy.
4. Select kubernetes.io/aws-ebs from the drop down list.
5. Enter additional parameters for the storage class as desired.
Click Create to create the storage class.

2.1.2. Creating the Persistent Volume Claim

Prerequisites

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift Container Platform.

Procedure

In the OpenShift Container Platform console, click Storage Persistent Volume Claims.
In the persistent volume claims overview, click Create Persistent Volume Claim.
Define the desired options on the page that appears.
1. Select the storage class created previously from the drop-down menu.
2. Enter a unique name for the storage claim.
3. Select the access mode. This determines the read and write access for the created storage claim.
4. Define the size of the storage claim.
Click Create to create the persistent volume claim and generate a persistent volume.

2.1.3. Volume Format

Before OpenShift Container Platform mounts the volume and passes it to a container, it checks that it contains a file system as specified by the fsType parameter in the persistent volume definition. If the device is not formatted with the file system, all data from the device is erased and the device is automatically formatted with the given file system.

This allows using unformatted AWS volumes as persistent volumes, because OpenShift Container Platform formats them before the first use.

2.1.4. Maximum Number of EBS Volumes on a Node

By default, OpenShift Container Platform supports a maximum of 39 EBS volumes attached to one node. This limit is consistent with the AWS volume limits.

OpenShift Container Platform can be configured to have a higher limit by setting the environment variable KUBE_MAX_PD_VOLS. However, AWS requires a particular naming scheme (AWS Device Naming) for attached devices, which only supports a maximum of 52 volumes. This limits the number of volumes that can be attached to a node via OpenShift Container Platform to 52.

2.2. Persistent storage using Fibre Channel

OpenShift Container Platform supports Fibre Channel, allowing you to provision your OpenShift Container Platform cluster with persistent storage using Fibre channel volumes. Some familiarity with Kubernetes and Fibre Channel is assumed.

The Kubernetes persistent volume framework allows administrators to provision a cluster with persistent storage and gives users a way to request those resources without having any knowledge of the underlying infrastructure. PersistentVolumes are not bound to a single project or namespace; they can be shared across the OpenShift Container Platform cluster. PersistentVolumeClaims are specific to a project or namespace and can be requested by users.

Important

High availability of storage in the infrastructure is left to the underlying storage provider.

Additional references

Fibre Channel

2.2.1. Provisioning

To provision Fibre Channel volumes using the PersistentVolume API the following must be available:

The targetWWNs (array of Fibre Channel target’s World Wide Names).
A valid LUN number.
The filesystem type.

A PersistentVolume and a LUN have a one-to-one mapping between them.

Prerequisites

Fibre Channel LUNs must exist in the underlying infrastructure.

PersistentVolume Object Definition

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0001
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  fc:
    targetWWNs: ['500a0981891b8dc5', '500a0981991b8dc5'] 1
    lun: 2
    fsType: ext4

1: Fibre Channel WWNs are identified as /dev/disk/by-path/pci-<IDENTIFIER>-fc-0x<WWN>-lun-<LUN#>, but you do not need to provide any part of the path leading up to the WWN, including the 0x, and anything after, including the - (hyphen).

Important

Changing the value of the fstype parameter after the volume has been formatted and provisioned can result in data loss and pod failure.

2.2.1.1. Enforcing disk quotas

Use LUN partitions to enforce disk quotas and size constraints. Each LUN is mapped to a single PersistentVolume, and unique names must be used for PersistentVolumes.

Enforcing quotas in this way allows the end user to request persistent storage by a specific amount, such as 10Gi, and be matched with a corresponding volume of equal or greater capacity.

2.2.1.2. Fibre Channel volume security

Users request storage with a PersistentVolumeClaim. This claim only lives in the user’s namespace, and can only be referenced by a pod within that same namespace. Any attempt to access a PersistentVolume across a namespace causes the pod to fail.

Each Fibre Channel LUN must be accessible by all nodes in the cluster.

2.3. Persistent storage using NFS

OpenShift Container Platform clusters can be provisioned with persistent storage using NFS. Persistent volumes (PVs) and persistent volume claims (PVCs) provide a convenient method for sharing a volume across a project. While the NFS-specific information contained in a PV definition could also be defined directly in a Pod definition, doing so does not create the volume as a distinct cluster resource, making the volume more susceptible to conflicts.

Additional resources

Network File System (NFS)

2.3.1. Provisioning

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift Container Platform. To provision NFS volumes, a list of NFS servers and export paths are all that is required.

Procedure

Create an object definition for the PV:
```
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv0001 1
spec:
  capacity:
    storage: 5Gi 2
  accessModes:
  - ReadWriteOnce 3
  nfs: 4
    path: /tmp 5
    server: 172.17.0.2 6
  persistentVolumeReclaimPolicy: Retain 7
```
1
The name of the volume. This is the PV identity in various oc <command> pod commands.
2
The amount of storage allocated to this volume.
3
Though this appears to be related to controlling access to the volume, it is actually used similarly to labels and used to match a PVC to a PV. Currently, no access rules are enforced based on the accessModes.
4
The volume type being used, in this case the nfs plug-in.
5
The path that is exported by the NFS server.
6
The host name or IP address of the NFS server.
7
The reclaim policy for the PV. This defines what happens to a volume when released.
Note
Each NFS volume must be mountable by all schedulable nodes in the cluster.

Verify that the PV was created:

$ oc get pv
NAME     LABELS    CAPACITY     ACCESSMODES   STATUS      CLAIM  REASON    AGE
pv0001   <none>    5Gi          RWO           Available                    31s

Create a persistent volume claim that binds to the new PV:
```
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nfs-claim1
spec:
  accessModes:
    - ReadWriteOnce 1
  resources:
    requests:
      storage: 5Gi 2
```
1
As mentioned above for PVs, the accessModes do not enforce security, but rather act as labels to match a PV to a PVC.
2
This claim looks for PVs offering 5Gi or greater capacity.

Verify that the persistent volume claim was created:

$ oc get pvc
NAME         STATUS   VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS   AGE
nfs-claim1   Bound    pv0001   5Gi        RWO            gp2            2m

2.3.2. Enforcing disk quotas

You can use disk partitions to enforce disk quotas and size constraints. Each partition can be its own export. Each export is one PV. OpenShift Container Platform enforces unique names for PVs, but the uniqueness of the NFS volume’s server and path is up to the administrator.

Enforcing quotas in this way allows the developer to request persistent storage by a specific amount, such as 10Gi, and be matched with a corresponding volume of equal or greater capacity.

2.3.3. NFS volume security

This section covers NFS volume security, including matching permissions and SELinux considerations. The user is expected to understand the basics of POSIX permissions, process UIDs, supplemental groups, and SELinux.

Developers request NFS storage by referencing either a PVC by name or the NFS volume plug-in directly in the volumes section of their Pod definition.

The /etc/exports file on the NFS server contains the accessible NFS directories. The target NFS directory has POSIX owner and group IDs. The OpenShift Container Platform NFS plug-in mounts the container’s NFS directory with the same POSIX ownership and permissions found on the exported NFS directory. However, the container is not run with its effective UID equal to the owner of the NFS mount, which is the desired behavior.

As an example, if the target NFS directory appears on the NFS server as:

$ ls -lZ /opt/nfs -d
drwxrws---. nfsnobody 5555 unconfined_u:object_r:usr_t:s0   /opt/nfs

$ id nfsnobody
uid=65534(nfsnobody) gid=65534(nfsnobody) groups=65534(nfsnobody)

Then the container must match SELinux labels, and either run with a UID of 65534, the nfsnobody owner, or with 5555 in its supplemental groups in order to access the directory.

Note

The owner ID of 65534 is used as an example. Even though NFS’s root_squash maps root, uid 0, to nfsnobody, uid 65534, NFS exports can have arbitrary owner IDs. Owner 65534 is not required for NFS exports.

2.3.3.1. Group IDs

The recommended way to handle NFS access, assuming it is not an option to change permissions on the NFS export, is to use supplemental groups. Supplemental groups in OpenShift Container Platform are used for shared storage, of which NFS is an example. In contrast block storage, such as iSCSI, use the fsGroup SCC strategy and the fsGroup value in the Pod’s securityContext.

Note

It is generally preferable to use supplemental group IDs to gain access to persistent storage versus using user IDs.

Because the group ID on the example target NFS directory is 5555, the Pod can define that group ID using supplementalGroups under the Pod’s securityContext definition. For example:

spec:
  containers:
    - name:
    ...
  securityContext: 1
    supplementalGroups: [5555] 2

1: securityContext must be defined at the Pod level, not under a specific container.
2: An array of GIDs defined for the Pod. In this case, there is one element in the array. Additional GIDs would be comma-separated.

Assuming there are no custom SCCs that might satisfy the Pod’s requirements, the Pod likely matches the restricted SCC. This SCC has the supplementalGroups strategy set to RunAsAny, meaning that any supplied group ID is accepted without range checking.

As a result, the above Pod passes admissions and is launched. However, if group ID range checking is desired, a custom SCC is the preferred solution. A custom SCC can be created such that minimum and maximum group IDs are defined, group ID range checking is enforced, and a group ID of 5555 is allowed.

Note

To use a custom SCC, you must first add it to the appropriate service account. For example, use the default service account in the given project unless another has been specified on the Pod specification.

2.3.3.2. User IDs

User IDs can be defined in the container image or in the Pod definition.

Note

It is generally preferable to use supplemental group IDs to gain access to persistent storage versus using user IDs.

In the example target NFS directory shown above, the container needs its UID set to 65534, ignoring group IDs for the moment, so the following can be added to the Pod definition:

spec:
  containers: 1
  - name:
  ...
    securityContext:
      runAsUser: 65534 2

1: Pods contain a securityContext specific to each container and a Pod’s securityContext which applies to all containers defined in the Pod.
2: 65534 is the nfsnobody user.

Assuming the default project and the restricted SCC, the Pod’s requested user ID of 65534 is not allowed, and therefore the Pod fails. The Pod fails for the following reasons:

It requests 65534 as its user ID.
All SCCs available to the Pod are examined to see which SCC allows a user ID of 65534. While all policies of the SCCs are checked, the focus here is on user ID.
Because all available SCCs use MustRunAsRange for their runAsUser strategy, UID range checking is required.
65534 is not included in the SCC or project’s user ID range.

It is generally considered a good practice not to modify the predefined SCCs. The preferred way to fix this situation is to create a custom SCC A custom SCC can be created such that minimum and maximum user IDs are defined, UID range checking is still enforced, and the UID of 65534 is allowed.

Note

2.3.3.3. SELinux

By default, SELinux does not allow writing from a Pod to a remote NFS server. The NFS volume mounts correctly, but is read-only.

To enable writing to a remote NFS server, follow the below procedure.

Prerequisites

The container-selinux package must be installed. This package provides the virt_use_nfs SELinux boolean.

Procedure

Enable the virt_use_nfs boolean using the following command. The -P option makes this boolean persistent across reboots.
```
# setsebool -P virt_use_nfs 1
```

2.3.3.4. Export settings

In order to enable arbitrary container users to read and write the volume, each exported volume on the NFS server should conform to the following conditions:

Every export must be exported using the following format:
```
/<example_fs> *(rw,root_squash)
```
The firewall must be configured to allow traffic to the mount point.
- For NFSv4, configure the default port 2049 (nfs).
  NFSv4
```
# iptables -I INPUT 1 -p tcp --dport 2049 -j ACCEPT
```
- For NFSv3, there are three ports to configure: 2049 (nfs), 20048 (mountd), and 111 (portmapper).
  NFSv3
```
# iptables -I INPUT 1 -p tcp --dport 2049 -j ACCEPT
# iptables -I INPUT 1 -p tcp --dport 20048 -j ACCEPT
# iptables -I INPUT 1 -p tcp --dport 111 -j ACCEPT
```
The NFS export and directory must be set up so that they are accessible by the target Pods. Either set the export to be owned by the container’s primary UID, or supply the Pod group access using supplementalGroups, as shown in group IDs above.

2.3.4. Reclaiming resources

NFS implements the OpenShift Container Platform Recyclable plug-in interface. Automatic processes handle reclamation tasks based on policies set on each persistent volume.

By default, PVs are set to Retain.

Once claim to a PVC is deleted, and the PV is released, the PV object should not be reused. Instead, a new PV should be created with the same basic volume details as the original.

For example, the administrator creates a PV named nfs1:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs1
spec:
  capacity:
    storage: 1Mi
  accessModes:
    - ReadWriteMany
  nfs:
    server: 192.168.1.1
    path: "/"

The user creates PVC1, which binds to nfs1. The user then deletes PVC1, releasing claim to nfs1. This results in nfs1 being Released. If the administrator wants to make the same NFS share available, they should create a new PV with the same NFS server details, but a different PV name:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs2
spec:
  capacity:
    storage: 1Mi
  accessModes:
    - ReadWriteMany
  nfs:
    server: 192.168.1.1
    path: "/"

Deleting the original PV and re-creating it with the same name is discouraged. Attempting to manually change the status of a PV from Released to Available causes errors and potential data loss.

2.3.5. Additional configuration and troubleshooting

Depending on what version of NFS is being used and how it is configured, there may be additional configuration steps needed for proper export and security mapping. The following are some that may apply:

NFSv4 mount incorrectly shows all files with ownership of `nobody:nobody`	Could be attributed to the ID mapping settings, found in `/etc/idmapd.conf` on your NFS. See this Red Hat Solution.
Disabling ID mapping on NFSv4	On both the NFS client and server, run: # echo 'Y' > /sys/module/nfsd/parameters/nfs4_disable_idmapping

2.4. Persistent storage using hostPath

A hostPath volume in an OpenShift Container Platform cluster mounts a file or directory from the host node’s filesystem into your Pod. Most Pods will not need a hostPath volume, but it does offer a quick option for testing should an application require it.

Important

The cluster administrator must configure Pods to run as privileged. This grants access to Pods in the same node.

2.4.1. Overview

OpenShift Container Platform supports hostPath mounting for development and testing on a single-node cluster.

In a production cluster, you would not use hostPath. Instead, a cluster administrator would provision a network resource, such as a GCE Persistent Disk volume, an NFS share, or an Amazon EBS volume. Network resources support the use of StorageClasses to set up dynamic provisioning.

A hostPath volume must be provisioned statically.

2.4.2. Statically provisioning hostPath volumes

A Pod that uses a hostPath volume must be referenced by manual (static) provisioning.

Procedure

Define the persistent volume (PV). Create a file, pv.yaml, with the PersistentVolume object definition:
```
  apiVersion: v1
  kind: PersistentVolume
  metadata:
    name: task-pv-volume 1
    labels:
      type: local
  spec:
    storageClassName: manual 2
    capacity:
      storage: 5Gi
    accessModes:
      - ReadWriteOnce 3
    persistentVolumeReclaimPolicy: Retain
    hostPath:
      path: "/mnt/data" 4
```
1
The name of the volume. This name is how it is identified by PersistentVolumeClaims or Pods.
2
Used to bind PersistentVolumeClaim requests to this PersistentVolume.
3
The volume can be mounted as read-write by a single node.
4
The configuration file specifies that the volume is at /mnt/data on the cluster’s node.
Create the PV from the file:
```
$ oc create -f pv.yaml
```

Define the persistent volume claim (PVC). Create a file, pvc.yaml, with the PersistentVolumeClaim object definition:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: task-pvc-volume
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: manual

Create the PVC from the file:
```
$ oc create -f pvc.yaml
```

2.4.3. Mounting the hostPath share in a privileged Pod

After the PersistentVolumeClaim has been created, it can be used inside by an application. The following example demonstrates mounting this share inside of a Pod.

Prerequisites

A PersistentVolumeClaim exists that is mapped to the underlying hostPath share.

Procedure

Create a privileged Pod that mounts the existing PersistentVolumeClaim:

apiVersion: v1
kind: Pod
metadata:
  name: pod-name 1
spec:
  containers:
    ...
    securityContext:
      privileged: true 2
    volumeMounts:
    - mountPath: /data 3
      name: hostpath-privileged
  ...
  securityContext: {}
  volumes:
    - name: hostpath-privileged
      persistentVolumeClaim:
        claimName: task-pvc-volume 4

1: The name of the Pod.
2: The Pod must run as privileged to access the node’s storage.
3: The path to mount the hostPath share inside the privileged Pod.
4: The name of the PersistentVolumeClaim that has been previously created.

2.5. Persistent Storage Using iSCSI

You can provision your OpenShift Container Platform cluster with persistent storage using iSCSI. Some familiarity with Kubernetes and iSCSI is assumed.

Important

Persistent storage using iSCSI is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

Important

High-availability of storage in the infrastructure is left to the underlying storage provider.

Important

When you use iSCSI on Amazon Web Services, you must update the default security policy to include TCP traffic between nodes on the iSCSI ports. By default, they are ports 860 and 3260.

Important

OpenShift assumes that all nodes in the cluster have already configured iSCSI initator, i.e. have installed iscsi-initiator-utils package and configured their initiator name in /etc/iscsi/initiatorname.iscsi. See Storage Administration Guide linked above.

2.5.1. Provisioning

Verify that the storage exists in the underlying infrastructure before mounting it as a volume in OpenShift Container Platform. All that is required for the iSCSI is the iSCSI target portal, a valid iSCSI Qualified Name (IQN), a valid LUN number, the filesystem type, and the PersistentVolume API.

Example 2.1. Persistent Volume Object Definition

apiVersion: v1
kind: PersistentVolume
metadata:
  name: iscsi-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  iscsi:
     targetPortal: 10.16.154.81:3260
     iqn: iqn.2014-12.example.server:storage.target00
     lun: 0
     fsType: 'ext4'

2.5.2. Enforcing Disk Quotas

Use LUN partitions to enforce disk quotas and size constraints. Each LUN is one persistent volume. Kubernetes enforces unique names for persistent volumes.

Enforcing quotas in this way allows the end user to request persistent storage by a specific amount (e.g, 10Gi) and be matched with a corresponding volume of equal or greater capacity.

2.5.3. iSCSI Volume Security

Users request storage with a PersistentVolumeClaim. This claim only lives in the user’s namespace and can only be referenced by a pod within that same namespace. Any attempt to access a persistent volume claim across a namespace causes the pod to fail.

Each iSCSI LUN must be accessible by all nodes in the cluster.

2.5.3.1. Challenge Handshake Authentication Protocol (CHAP) configuration

Optionally, OpenShift can use CHAP to authenticate itself to iSCSI targets:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: iscsi-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  iscsi:
    targetPortal: 10.0.0.1:3260
    iqn: iqn.2016-04.test.com:storage.target00
    lun: 0
    fsType: ext4
    chapAuthDiscovery: true 1
    chapAuthSession: true 2
    secretRef:
      name: chap-secret 3

1: Enable CHAP authentication of iSCSI discovery.
2: Enable CHAP authentication of iSCSI session.
3: Specify name of Secrets object with user name + password. This Secrets object must be available in all namespaces that can use the referenced volume.

2.5.4. iSCSI Multipathing

For iSCSI-based storage, you can configure multiple paths by using the same IQN for more than one target portal IP address. Multipathing ensures access to the persistent volume when one or more of the components in a path fail.

To specify multi-paths in the pod specification use the portals field. For example:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: iscsi-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  iscsi:
    targetPortal: 10.0.0.1:3260
    portals: ['10.0.2.16:3260', '10.0.2.17:3260', '10.0.2.18:3260'] 1
    iqn: iqn.2016-04.test.com:storage.target00
    lun: 0
    fsType: ext4
    readOnly: false

1: Add additional target portals using the portals field.

2.5.5. iSCSI Custom Initiator IQN

Configure the custom initiator iSCSI Qualified Name (IQN) if the iSCSI targets are restricted to certain IQNs, but the nodes that the iSCSI PVs are attached to are not guaranteed to have these IQNs.

To specify a custom initiator IQN, use initiatorName field.

apiVersion: v1
kind: PersistentVolume
metadata:
  name: iscsi-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  iscsi:
    targetPortal: 10.0.0.1:3260
    portals: ['10.0.2.16:3260', '10.0.2.17:3260', '10.0.2.18:3260']
    iqn: iqn.2016-04.test.com:storage.target00
    lun: 0
    initiatorName: iqn.2016-04.test.com:custom.iqn 1
    fsType: ext4
    readOnly: false

1: Specify the name of the initiator.

2.6. Persistent storage using the Container Storage Interface (CSI)

The Container Storage Interface (CSI) allows OpenShift Container Platform to consume storage from storage backends that implement the CSI interface as persistent storage.

Important

Container Storage Interface is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

Note

OpenShift Container Platform does not ship with any CSI drivers. It is recommended to use the CSI drivers provided by community or storage vendors.

OpenShift Container Platform 4.1 supports version 1.0.0 of the CSI specification.

2.6.1. CSI Architecture

CSI drivers are typically shipped as container images. These containers are not aware of OpenShift Container Platform where they run. To use CSI-compatible storage backend in OpenShift Container Platform, the cluster administrator must deploy several components that serve as a bridge between OpenShift Container Platform and the storage driver.

The following diagram provides a high-level overview about the components running in pods in the OpenShift Container Platform cluster.

It is possible to run multiple CSI drivers for different storage backends. Each driver needs its own external controllers' deployment and DaemonSet with the driver and CSI registrar.

2.6.1.1. External CSI controllers

External CSI Controllers is a deployment that deploys one or more pods with three containers:

An external CSI attacher container translates attach and detach calls from OpenShift Container Platform to respective ControllerPublish and ControllerUnpublish calls to the CSI driver.
An external CSI provisioner container that translates provision and delete calls from OpenShift Container Platform to respective CreateVolume and DeleteVolume calls to the CSI driver.
A CSI driver container

The CSI attacher and CSI provisioner containers communicate with the CSI driver container using UNIX Domain Sockets, ensuring that no CSI communication leaves the pod. The CSI driver is not accessible from outside of the pod.

Note

attach, detach, provision, and delete operations typically require the CSI driver to use credentials to the storage backend. Run the CSI controller pods on infrastructure nodes so the credentials are never leaked to user processes, even in the event of a catastrophic security breach on a compute node.

Note

The external attacher must also run for CSI drivers that do not support third-party attach or detach operations. The external attacher will not issue any ControllerPublish or ControllerUnpublish operations to the CSI driver. However, it still must run to implement the necessary OpenShift Container Platform attachment API.

2.6.1.2. CSI Driver DaemonSet

The CSI driver DaemonSet runs a pod on every node that allows OpenShift Container Platform to mount storage provided by the CSI driver to the node and use it in user workloads (pods) as persistent volumes (PVs). The pod with the CSI driver installed contains the following containers:

A CSI driver registrar, which registers the CSI driver into the openshift-node service running on the node. The openshift-node process running on the node then directly connects with the CSI driver using the UNIX Domain Socket available on the node.
A CSI driver.

The CSI driver deployed on the node should have as few credentials to the storage backend as possible. OpenShift Container Platform will only use the node plug-in set of CSI calls such as NodePublish/NodeUnpublish and NodeStage/NodeUnstage, if these calls are implemented.

2.6.2. Dynamic Provisioning

Dynamic provisioning of persistent storage depends on the capabilities of the CSI driver and underlying storage backend. The provider of the CSI driver should document how to create a StorageClass in OpenShift Container Platform and the parameters available for configuration.

As seen in the OpenStack Cinder example, you can deploy this StorageClass to enable dynamic provisioning.

Procedure

Create a default storage class that ensures all PVCs that do not require any special storage class are provisioned by the installed CSI driver.

# oc create -f - << EOF
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: cinder
  annotations:
    storageclass.kubernetes.io/is-default-class: "true"
provisioner: csi-cinderplugin
parameters:
EOF

2.6.3. Example using the CSI driver

The following example installs a default MySQL template without any changes to the template.

Prerequisites

The CSI driver has been deployed.
A StorageClass has been created for dynamic provisioning.

Procedure

Create the MySQL template:

# oc new-app mysql-persistent
--> Deploying template "openshift/mysql-persistent" to project default
...

# oc get pvc
NAME              STATUS    VOLUME                                   CAPACITY
ACCESS MODES   STORAGECLASS   AGE
mysql             Bound     kubernetes-dynamic-pv-3271ffcb4e1811e8   1Gi
RWO            cinder         3s

2.7. Persistent storage using VMware vSphere volumes

OpenShift Container Platform allows use of VMware vSphere’s Virtual Machine Disk (VMDK) volumes. You can provision your OpenShift Container Platform cluster with persistent storage using VMware vSphere. Some familiarity with Kubernetes and VMware vSphere is assumed.

VMware vSphere volumes can be provisioned dynamically. OpenShift Container Platform creates the disk in vSphere and attaches this disk to the correct image.

PersistentVolumes are not bound to a single project or namespace; they can be shared across the OpenShift Container Platform cluster. PersistentVolumeClaims are specific to a project or namespace and can be requested by users.

Additional references

VMware vSphere

2.7.1. Dynamically provisioning VMware vSphere volumes

Dynamically provisioning VMware vSphere volumes is the recommended method.

Prerequisites

An OpenShift Container Platform cluster installed on a VMware vSphere version that meets the requirements for the components that you use. See Installing a cluster on vSphere

You can use either of the following procedures to dynamically provision these volumes using the default StorageClass.

2.7.1.1. Dynamically provisioning VMware vSphere volumes using the UI

OpenShift Container Platform installs a default StorageClass, named thin, that uses the thin disk format for provisioning volumes.

Prerequisites

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift Container Platform.

Procedure

In the OpenShift Container Platform console, click Storage Persistent Volume Claims.
In the persistent volume claims overview, click Create Persistent Volume Claim.
Define the required options on the resulting page.
1. Select the thin StorageClass.
2. Enter a unique name for the storage claim.
3. Select the access mode to determine the read and write access for the created storage claim.
4. Define the size of the storage claim.
Click Create to create the PersistentVolumeClaim and generate a PersistentVolume.

2.7.1.2. Dynamically provisioning VMware vSphere volumes using the CLI

OpenShift Container Platform installs a default StorageClass, named thin, that uses the thin disk format for provisioning volumes.

Prerequisites

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift Container Platform.

Procedure (CLI)

You can define a VMware vSphere PersistentVolumeClaim by creating a file, pvc.yaml, with the following contents:
```
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: pvc 1
spec:
  accessModes:
  - ReadWriteOnce 2
  resources:
    requests:
      storage: 1Gi 3
```
1
A unique name that represents the PersistentVolumeClaim.
2
The PersistentVolumeClaim’s access mode. With ReadWriteOnce, the volume can be mounted with read and write permissions by a single node.
3
The size of the PersistentVolumeClaim.
Create the PersistentVolumeClaim from the file:
```
$ oc create -f pvc.yaml
```

2.7.2. Statically provisioning VMware vSphere volumes

To statically provision VMware vSphere volumes you must create the virtual machine disks for reference by the persistent volume framework.

Prerequisites

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift Container Platform.

Procedure

Create the virtual machine disks. Virtual machine disks (VMDKs) must be created manually before statically provisioning VMware vSphere volumes. Use either of the following methods:
- Create using vmkfstools. Access ESX through Secure Shell (SSH) and then use following command to create a VMDK volume:
```
$ vmkfstools -c <size> /vmfs/volumes/DatastoreName/volumes/<disk-name>.vmdk
```
- Create using vmware-diskmanager:
```
$ shell vmware-vdiskmanager -c -t 0 -s <size> -a lsilogic <disk-name>.vmdk
```
Create a PersistentVolume that references the VMDKs. Create a file, pv.yaml, with the PersistentVolume object definition:
```
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv 1
spec:
  capacity:
    storage: 2Gi 2
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  vsphereVolume: 3
    volumePath: "[datastore1] volumes/myDisk"  4
    fsType: ext4  5
```
1
The name of the volume. This name is how it is identified by PersistentVolumeClaims or Pods.
2
The amount of storage allocated to this volume.
3
The volume type used, with vsphereVolume for vSphere volumes. The label is used to mount a vSphere VMDK volume into pods. The contents of a volume are preserved when it is unmounted. The volume type supports VMFS and VSAN datastore.
4
The existing VMDK volume to use. You must enclose the datastore name in square brackets, [], in the volume definition, as shown previously.
5
The file system type to mount. For example, ext4, xfs, or other file-systems.
Important
Changing the value of the fsType parameter after the volume is formatted and provisioned can result in data loss and Pod failure.
Create the PersistentVolume from the file:
```
$ oc create -f pv.yaml
```

2.7.2.1. Formatting VMware vSphere volumes

Before OpenShift Container Platform mounts the volume and passes it to a container, it checks that the volume contains a file system that is specified by the fsType parameter value in the PersistentVolume (PV) definition. If the device is not formatted with the file system, all data from the device is erased, and the device is automatically formatted with the specified file system.

Because OpenShift Container Platform formats them before the first use, you can use unformatted vSphere volumes as PVs.

2.8. Persistent storage using volume snapshots

This document describes how to use VolumeSnapshots to protect against data loss in OpenShift Container Platform. Familiarity with persistent volumes is suggested.

Important

Volume Snapshot is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

2.8.1. About snapshots

A volume snapshot is a snapshot taken from a storage volume in a cluster. The external snapshot controller and provisioner enable use of the feature in the OpenShift Container Platform cluster and handle volume snapshots through the OpenShift Container Platform API.

With volume snapshots, a cluster administrator can:

Create a snapshot of a PersistentVolume bound to a PersistentVolumeClaim.
List existing VolumeSnapshots.
Delete an existing VolumeSnapshot.
Create a new PersistentVolume from an existing VolumeSnapshot.

Supported PersistentVolume types:

AWS Elastic Block Store (EBS)
Google Compute Engine (GCE) Persistent Disk (PD)

2.8.2. External controller and provisioner

The controller and provisioner provide volume snapshotting. These external components run in the cluster.

There are two external components that provide volume snapshotting:

External controller: Creates, deletes, and reports events on volume snapshots.
External provisioner: Creates new PersistentVolumes from VolumeSnapshots.

The external controller and provisioner services are distributed as container images and can be run in the OpenShift Container Platform cluster as usual.

2.8.2.1. Running the external controller and provisioner

The cluster administrator must configure access to run the external controller and provisioner.

Procedure

To allow the containers managing the API objects:

Create a ServiceAccount and ClusterRole:

apiVersion: v1
kind: ServiceAccount
metadata:
  name: snapshot-controller-runner
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: snapshot-controller-role
rules:
  - apiGroups: [""]
    resources: ["persistentvolumes"]
    verbs: ["get", "list", "watch", "create", "delete"]
  - apiGroups: [""]
    resources: ["persistentvolumeclaims"]
    verbs: ["get", "list", "watch", "update"]
  - apiGroups: ["storage.k8s.io"]
    resources: ["storageclasses"]
    verbs: ["get", "list", "watch"]
  - apiGroups: [""]
    resources: ["events"]
    verbs: ["list", "watch", "create", "update", "patch"]
  - apiGroups: ["apiextensions.k8s.io"]
    resources: ["customresourcedefinitions"]
    verbs: ["create", "list", "watch", "delete"]
  - apiGroups: ["volumesnapshot.external-storage.k8s.io"]
    resources: ["volumesnapshots"]
    verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]
  - apiGroups: ["volumesnapshot.external-storage.k8s.io"]
    resources: ["volumesnapshotdatas"]
    verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]

As the cluster administrator, provide the hostNetwork security context constraint (SCC):
```
# oc adm policy add-scc-to-user hostnetwork -z snapshot-controller-runner
```
This SCC controls access to the snapshot-controller-runner service account that the Pod is using.

Bind the rules via ClusterRoleBinding:

apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: snapshot-controller
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: snapshot-controller-role
subjects:
- kind: ServiceAccount
  name: snapshot-controller-runner
  namespace: default 1

1: Specify the project name where the snapshot-controller resides.

2.8.2.2. AWS and GCE authentication

To authenticate the external controller and provisioner, your cloud provider may require the administrator to provide a secret.

2.8.2.2.1. AWS authentication

If the external controller and provisioner are deployed in Amazon Web Services (AWS), AWS must be able to authenticate using the access key.

To provide the credential to the Pod, the cluster administrator creates a new secret:

apiVersion: v1
kind: Secret
metadata:
  name: awskeys
type: Opaque
data:
  access-key-id: <base64 encoded AWS_ACCESS_KEY_ID>
  secret-access-key: <base64 encoded AWS_SECRET_ACCESS_KEY>

Important

When generating the base64 values required for the awskeys secret, remove any trailing newline character as follows:

$ echo -n "<aws_access_key_id>" | base64
$ echo -n "<aws_secret_access_key>" | base64

The following example displays the AWS deployment of the external controller and provisioner containers. Both Pod containers use the secret to access the AWS API.

kind: Deployment
apiVersion: extensions/v1beta1
metadata:
  name: snapshot-controller
spec:
  replicas: 1
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: snapshot-controller
    spec:
      serviceAccountName: snapshot-controller-runner
      hostNetwork: true
      containers:
        - name: snapshot-controller
          image: "registry.redhat.io/openshift3/snapshot-controller:latest"
          imagePullPolicy: "IfNotPresent"
          args: ["-cloudprovider", "aws"]
          env:
            - name: AWS_ACCESS_KEY_ID
              valueFrom:
                secretKeyRef:
                  name: awskeys
                  key: access-key-id
            - name: AWS_SECRET_ACCESS_KEY
              valueFrom:
                secretKeyRef:
                  name: awskeys
                  key: secret-access-key
        - name: snapshot-provisioner
          image: "registry.redhat.io/openshift3/snapshot-provisioner:latest"
          imagePullPolicy: "IfNotPresent"
          args: ["-cloudprovider", "aws"]
          env:
            - name: AWS_ACCESS_KEY_ID
              valueFrom:
                secretKeyRef:
                  name: awskeys
                  key: access-key-id
            - name: AWS_SECRET_ACCESS_KEY
              valueFrom:
                secretKeyRef:
                  name: awskeys
                  key: secret-access-key

2.8.2.2.2. GCE authentication

For Google Compute Engine (GCE), there is no need to use secrets to access the GCE API.

The administrator can proceed with the deployment as shown in the following example:

kind: Deployment
apiVersion: extensions/v1beta1
metadata:
  name: snapshot-controller
spec:
  replicas: 1
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: snapshot-controller
    spec:
      serviceAccountName: snapshot-controller-runner
      containers:
        - name: snapshot-controller
          image: "registry.redhat.io/openshift3/snapshot-controller:latest"
          imagePullPolicy: "IfNotPresent"
          args: ["-cloudprovider", "gce"]
        - name: snapshot-provisioner
          image: "registry.redhat.io/openshift3/snapshot-provisioner:latest"
          imagePullPolicy: "IfNotPresent"
          args: ["-cloudprovider", "gce"]

2.8.2.3. Managing snapshot users

Depending on the cluster configuration, it might be necessary to allow non-administrator users to manipulate the VolumeSnapshot objects on the API server. This can be done by creating a ClusterRole bound to a particular user or group.

For example, assume the user "alice" needs to work with snapshots in the cluster. The cluster administrator completes the following steps:

Define a new ClusterRole:

apiVersion: v1
kind: ClusterRole
metadata:
  name: volumesnapshot-admin
rules:
- apiGroups:
  - "volumesnapshot.external-storage.k8s.io"
  attributeRestrictions: null
  resources:
  - volumesnapshots
  verbs:
  - create
  - delete
  - deletecollection
  - get
  - list
  - patch
  - update
  - watch

Bind the cluster role to the user "alice" by creating a ClusterRoleBinding object:

apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: volumesnapshot-admin
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: volumesnapshot-admin
subjects:
- kind: User
  name: alice

Note

This is only an example of API access configuration. The VolumeSnapshot objects behave similar to other OpenShift Container Platform API objects. See the API access control documentation for more information on managing the API RBAC.

2.8.3. Creating and deleting snapshots

Similar to how a persistent volume claim (PVC) binds to a persistent volume (PV) to provision a volume, VolumeSnapshotData and VolumeSnapshot are used to create a volume snapshot.

Volume snapshots must use a supported PersistentVolume type.

2.8.3.1. Create snapshot

To take a snapshot of a PV, create a new VolumeSnapshotData object based on the VolumeSnapshot, as shown in the following example:

apiVersion: volumesnapshot.external-storage.k8s.io/v1
kind: VolumeSnapshot 1
metadata:
  name: snapshot-demo
spec:
  persistentVolumeClaimName: ebs-pvc 2

1: A VolumeSnapshotData object is automatically created based on the VolumeSnapshot.
2: persistentVolumeClaimName is the name of the PersistentVolumeClaim bound to a PersistentVolume. This particular PV is snapshotted.

Depending on the PV type, the create snapshot operation might go through several phases, which are reflected by the VolumeSnapshot status:

Create the new VolumeSnapshot object.
Start the controller. The snapshotted PersistentVolume might need to be frozen and the applications paused.
Create ("cut") the snapshot. The snapshotted PersistentVolume might return to normal operation, but the snapshot itself is not yet ready (status=True, type=Pending).
Create the new VolumeSnapshotData object, representing the actual snapshot.
The snapshot is complete and ready to use (status=True, type=Ready).

Important

It is the user’s responsibility to ensure data consistency (stop the Pod or application, flush caches, freeze the file system, and so on).

Note

In case of error, the VolumeSnapshot status is appended with an Error condition.

To display the VolumeSnapshot status:

$ oc get volumesnapshot -o yaml

The status is displayed, as shown in the following example:

apiVersion: volumesnapshot.external-storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  clusterName: ""
  creationTimestamp: 2017-09-19T13:58:28Z
  generation: 0
  labels:
    Timestamp: "1505829508178510973"
  name: snapshot-demo
  namespace: default 1
  resourceVersion: "780"
  selfLink: /apis/volumesnapshot.external-storage.k8s.io/v1/namespaces/default/volumesnapshots/snapshot-demo
  uid: 9cc5da57-9d42-11e7-9b25-90b11c132b3f
spec:
  persistentVolumeClaimName: ebs-pvc
  snapshotDataName: k8s-volume-snapshot-9cc8813e-9d42-11e7-8bed-90b11c132b3f
status:
  conditions:
  - lastTransitionTime: null
    message: Snapshot created successfully
    reason: ""
    status: "True"
    type: Ready
  creationTimestamp: null

1: Specify the project name where the snapshot-controller resides.

2.8.3.2. Restore snapshot

A PVC is used to restore a snapshot. But first, the administrator must create a StorageClass to restore a PersistentVolume from an existing VolumeSnapshot.

Create a StorageClass:

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: snapshot-promoter
provisioner: volumesnapshot.external-storage.k8s.io/snapshot-promoter
parameters: 1
  encrypted: "true"
  type: gp2

1: If you are using AWS EBS storage with gp2 encryption configured, you must set the parameters for encrypted and type.

Create a PVC:
```
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: snapshot-pv-provisioning-demo
  annotations:
    snapshot.alpha.kubernetes.io/snapshot: snapshot-demo 1
spec:
  storageClassName: snapshot-promoter 2
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi 3
```
1
The name of the VolumeSnapshot to be restored.
2
Created by the administrator for restoring VolumeSnapshots.
3
Storage size for a restored snapshot must be large enough to accommodate the original PV size.
A new PersistentVolume is created and bound to the PersistentVolumeClaim. The process might take several minutes depending on the PV type.

2.8.3.3. Delete snapshot

To delete a VolumeSnapshot:

$ oc delete volumesnapshot/<snapshot-name>

The VolumeSnapshotData bound to the VolumeSnapshot is automatically deleted.

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Chapter 2. Configuring persistent storage

2.1. Persistent Storage Using AWS Elastic Block Store

2.1.1. Creating the EBS Storage Class

2.1.2. Creating the Persistent Volume Claim

2.1.3. Volume Format

2.1.4. Maximum Number of EBS Volumes on a Node

2.2. Persistent storage using Fibre Channel

2.2.1. Provisioning

2.2.1.1. Enforcing disk quotas

2.2.1.2. Fibre Channel volume security

2.3. Persistent storage using NFS

2.3.1. Provisioning

2.3.2. Enforcing disk quotas

2.3.3. NFS volume security

2.3.3.1. Group IDs

2.3.3.2. User IDs

2.3.3.3. SELinux

2.3.3.4. Export settings

2.3.4. Reclaiming resources

2.3.5. Additional configuration and troubleshooting

2.4. Persistent storage using hostPath

2.4.1. Overview

2.4.2. Statically provisioning hostPath volumes

2.4.3. Mounting the hostPath share in a privileged Pod

2.5. Persistent Storage Using iSCSI

2.5.1. Provisioning

2.5.2. Enforcing Disk Quotas

2.5.3. iSCSI Volume Security

2.5.3.1. Challenge Handshake Authentication Protocol (CHAP) configuration

2.5.4. iSCSI Multipathing

2.5.5. iSCSI Custom Initiator IQN

2.6. Persistent storage using the Container Storage Interface (CSI)

2.6.1. CSI Architecture

2.6.1.1. External CSI controllers

2.6.1.2. CSI Driver DaemonSet

2.6.2. Dynamic Provisioning

2.6.3. Example using the CSI driver

2.7. Persistent storage using VMware vSphere volumes

2.7.1. Dynamically provisioning VMware vSphere volumes

2.7.1.1. Dynamically provisioning VMware vSphere volumes using the UI

2.7.1.2. Dynamically provisioning VMware vSphere volumes using the CLI

2.7.2. Statically provisioning VMware vSphere volumes

2.7.2.1. Formatting VMware vSphere volumes

2.8. Persistent storage using volume snapshots

2.8.1. About snapshots

2.8.2. External controller and provisioner

2.8.2.1. Running the external controller and provisioner

2.8.2.2. AWS and GCE authentication

2.8.2.2.1. AWS authentication

2.8.2.2.2. GCE authentication

2.8.2.3. Managing snapshot users

2.8.3. Creating and deleting snapshots

2.8.3.1. Create snapshot

2.8.3.2. Restore snapshot

2.8.3.3. Delete snapshot

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