--- reviewers: - jsafrane - saad-ali - thockin - msau42 title: Volumes content_template: templates/concept weight: 10 --- {{% capture overview %}} On-disk files in a Container are ephemeral, which presents some problems for non-trivial applications when running in Containers. First, when a Container crashes, kubelet will restart it, but the files will be lost - the Container starts with a clean state. Second, when running Containers together in a `Pod` it is often necessary to share files between those Containers. The Kubernetes `Volume` abstraction solves both of these problems. Familiarity with [Pods](/docs/user-guide/pods) is suggested. {{% /capture %}} {{< toc >}} {{% capture body %}} ## Background Docker also has a concept of [volumes](https://docs.docker.com/engine/admin/volumes/), though it is somewhat looser and less managed. In Docker, a volume is simply a directory on disk or in another Container. Lifetimes are not managed and until very recently there were only local-disk-backed volumes. Docker now provides volume drivers, but the functionality is very limited for now (e.g. as of Docker 1.7 only one volume driver is allowed per Container and there is no way to pass parameters to volumes). A Kubernetes volume, on the other hand, has an explicit lifetime - the same as the Pod that encloses it. Consequently, a volume outlives any Containers that run within the Pod, and data is preserved across Container restarts. Of course, when a Pod ceases to exist, the volume will cease to exist, too. Perhaps more importantly than this, Kubernetes supports many types of volumes, and a Pod can use any number of them simultaneously. At its core, a volume is just a directory, possibly with some data in it, which is accessible to the Containers in a Pod. How that directory comes to be, the medium that backs it, and the contents of it are determined by the particular volume type used. To use a volume, a Pod specifies what volumes to provide for the Pod (the `.spec.volumes` field) and where to mount those into Containers (the `.spec.containers.volumeMounts` field). A process in a container sees a filesystem view composed from their Docker image and volumes. The [Docker image](https://docs.docker.com/userguide/dockerimages/) is at the root of the filesystem hierarchy, and any volumes are mounted at the specified paths within the image. Volumes can not mount onto other volumes or have hard links to other volumes. Each Container in the Pod must independently specify where to mount each volume. ## Types of Volumes Kubernetes supports several types of Volumes: * [awsElasticBlockStore](#awselasticblockstore) * [azureDisk](#azuredisk) * [azureFile](#azurefile) * [cephfs](#cephfs) * [configMap](#configmap) * [csi](#csi) * [downwardAPI](#downwardapi) * [emptyDir](#emptydir) * [fc (fibre channel)](#fc) * [flocker](#flocker) * [gcePersistentDisk](#gcepersistentdisk) * [gitRepo (deprecated)](#gitrepo) * [glusterfs](#glusterfs) * [hostPath](#hostpath) * [iscsi](#iscsi) * [local](#local) * [nfs](#nfs) * [persistentVolumeClaim](#persistentvolumeclaim) * [projected](#projected) * [portworxVolume](#portworxvolume) * [quobyte](#quobyte) * [rbd](#rbd) * [scaleIO](#scaleio) * [secret](#secret) * [storageos](#storageos) * [vsphereVolume](#vspherevolume) We welcome additional contributions. ### awsElasticBlockStore {#awselasticblockstore} An `awsElasticBlockStore` volume mounts an Amazon Web Services (AWS) [EBS Volume](http://aws.amazon.com/ebs/) into your Pod. Unlike `emptyDir`, which is erased when a Pod is removed, the contents of an EBS volume are preserved and the volume is merely unmounted. This means that an EBS volume can be pre-populated with data, and that data can be "handed off" between Pods. {{< caution >}} **Important:** You must create an EBS volume using `aws ec2 create-volume` or the AWS API before you can use it. {{< /caution >}} There are some restrictions when using an `awsElasticBlockStore` volume: * the nodes on which Pods are running must be AWS EC2 instances * those instances need to be in the same region and availability-zone as the EBS volume * EBS only supports a single EC2 instance mounting a volume #### Creating an EBS volume Before you can use an EBS volume with a Pod, you need to create it. ```shell aws ec2 create-volume --availability-zone=eu-west-1a --size=10 --volume-type=gp2 ``` Make sure the zone matches the zone you brought up your cluster in. (And also check that the size and EBS volume type are suitable for your use!) #### AWS EBS Example configuration ```yaml apiVersion: v1 kind: Pod metadata: name: test-ebs spec: containers: - image: k8s.gcr.io/test-webserver name: test-container volumeMounts: - mountPath: /test-ebs name: test-volume volumes: - name: test-volume # This AWS EBS volume must already exist. awsElasticBlockStore: volumeID: fsType: ext4 ``` ### azureDisk {#azuredisk} A `azureDisk` is used to mount a Microsoft Azure [Data Disk](https://azure.microsoft.com/en-us/documentation/articles/virtual-machines-linux-about-disks-vhds/) into a Pod. More details can be found [here](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/azure_disk/README.md). ### azureFile {#azurefile} A `azureFile` is used to mount a Microsoft Azure File Volume (SMB 2.1 and 3.0) into a Pod. More details can be found [here](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/azure_file/README.md). ### cephfs {#cephfs} A `cephfs` volume allows an existing CephFS volume to be mounted into your Pod. Unlike `emptyDir`, which is erased when a Pod is removed, the contents of a `cephfs` volume are preserved and the volume is merely unmounted. This means that a CephFS volume can be pre-populated with data, and that data can be "handed off" between Pods. CephFS can be mounted by multiple writers simultaneously. {{< caution >}} **Important:** You must have your own Ceph server running with the share exported before you can use it. {{< /caution >}} See the [CephFS example](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/cephfs/) for more details. ### configMap {#configmap} The [`configMap`](/docs/tasks/configure-pod-container/configure-pod-configmap/) resource provides a way to inject configuration data into Pods. The data stored in a `ConfigMap` object can be referenced in a volume of type `configMap` and then consumed by containerized applications running in a Pod. When referencing a `configMap` object, you can simply provide its name in the volume to reference it. You can also customize the path to use for a specific entry in the ConfigMap. For example, to mount the `log-config` ConfigMap onto a Pod called `configmap-pod`, you might use the YAML below: ```yaml apiVersion: v1 kind: Pod metadata: name: configmap-pod spec: containers: - name: test image: busybox volumeMounts: - name: config-vol mountPath: /etc/config volumes: - name: config-vol configMap: name: log-config items: - key: log_level path: log_level ``` The `log-config` ConfigMap is mounted as a volume, and all contents stored in its `log_level` entry are mounted into the Pod at path "`/etc/config/log_level`". Note that this path is derived from the volume's `mountPath` and the `path` keyed with `log_level`. {{< caution >}} **Important:** You must create a [ConfigMap](/docs/tasks/configure-pod-container/configure-pod-configmap/) before you can use it. {{< /caution >}} {{< note >}} **Note:** A Container using a ConfigMap as a [subPath](#using-subpath) volume mount will not receive ConfigMap updates. {{< /note >}} ### downwardAPI {#downwardapi} A `downwardAPI` volume is used to make downward API data available to applications. It mounts a directory and writes the requested data in plain text files. {{< note >}} **Note:** A Container using Downward API as a [subPath](#using-subpath) volume mount will not receive Downward API updates. {{< /note >}} See the [`downwardAPI` volume example](/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/) for more details. ### emptyDir {#emptydir} An `emptyDir` volume is first created when a Pod is assigned to a Node, and exists as long as that Pod is running on that node. As the name says, it is initially empty. Containers in the Pod can all read and write the same files in the `emptyDir` volume, though that volume can be mounted at the same or different paths in each Container. When a Pod is removed from a node for any reason, the data in the `emptyDir` is deleted forever. {{< note >}} **Note:** A Container crashing does *NOT* remove a Pod from a node, so the data in an `emptyDir` volume is safe across Container crashes. {{< /note >}} Some uses for an `emptyDir` are: * scratch space, such as for a disk-based merge sort * checkpointing a long computation for recovery from crashes * holding files that a content-manager Container fetches while a webserver Container serves the data By default, `emptyDir` volumes are stored on whatever medium is backing the node - that might be disk or SSD or network storage, depending on your environment. However, you can set the `emptyDir.medium` field to `"Memory"` to tell Kubernetes to mount a tmpfs (RAM-backed filesystem) for you instead. While tmpfs is very fast, be aware that unlike disks, tmpfs is cleared on node reboot and any files you write will count against your Container's memory limit. #### Example Pod ```yaml apiVersion: v1 kind: Pod metadata: name: test-pd spec: containers: - image: k8s.gcr.io/test-webserver name: test-container volumeMounts: - mountPath: /cache name: cache-volume volumes: - name: cache-volume emptyDir: {} ``` ### fc (fibre channel) {#fc} An `fc` volume allows an existing fibre channel volume to be mounted in a Pod. You can specify single or multiple target World Wide Names using the parameter `targetWWNs` in your volume configuration. If multiple WWNs are specified, targetWWNs expect that those WWNs are from multi-path connections. {{< caution >}} **Important:** You must configure FC SAN Zoning to allocate and mask those LUNs (volumes) to the target WWNs beforehand so that Kubernetes hosts can access them. {{< /caution >}} See the [FC example](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/fibre_channel) for more details. ### flocker {#flocker} [Flocker](https://github.com/ClusterHQ/flocker) is an open-source clustered Container data volume manager. It provides management and orchestration of data volumes backed by a variety of storage backends. A `flocker` volume allows a Flocker dataset to be mounted into a Pod. If the dataset does not already exist in Flocker, it needs to be first created with the Flocker CLI or by using the Flocker API. If the dataset already exists it will be reattached by Flocker to the node that the Pod is scheduled. This means data can be "handed off" between Pods as required. {{< caution >}} **Important:** You must have your own Flocker installation running before you can use it. {{< /caution >}} See the [Flocker example](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/flocker) for more details. ### gcePersistentDisk {#gcepersistentdisk} A `gcePersistentDisk` volume mounts a Google Compute Engine (GCE) [Persistent Disk](http://cloud.google.com/compute/docs/disks) into your Pod. Unlike `emptyDir`, which is erased when a Pod is removed, the contents of a PD are preserved and the volume is merely unmounted. This means that a PD can be pre-populated with data, and that data can be "handed off" between Pods. {{< caution >}} **Important:** You must create a PD using `gcloud` or the GCE API or UI before you can use it. {{< /caution >}} There are some restrictions when using a `gcePersistentDisk`: * the nodes on which Pods are running must be GCE VMs * those VMs need to be in the same GCE project and zone as the PD A feature of PD is that they can be mounted as read-only by multiple consumers simultaneously. This means that you can pre-populate a PD with your dataset and then serve it in parallel from as many Pods as you need. Unfortunately, PDs can only be mounted by a single consumer in read-write mode - no simultaneous writers allowed. Using a PD on a Pod controlled by a ReplicationController will fail unless the PD is read-only or the replica count is 0 or 1. #### Creating a PD Before you can use a GCE PD with a Pod, you need to create it. ```shell gcloud compute disks create --size=500GB --zone=us-central1-a my-data-disk ``` #### Example Pod ```yaml apiVersion: v1 kind: Pod metadata: name: test-pd spec: containers: - image: k8s.gcr.io/test-webserver name: test-container volumeMounts: - mountPath: /test-pd name: test-volume volumes: - name: test-volume # This GCE PD must already exist. gcePersistentDisk: pdName: my-data-disk fsType: ext4 ``` #### Regional Persistent Disks {{< feature-state for_k8s_version="v1.10" state="beta" >}} The [Regional Persistent Disks](https://cloud.google.com/compute/docs/disks/#repds) feature allows the creation of Persistent Disks that are available in two zones within the same region. In order to use this feature, the volume must be provisioned as a PersistentVolume; referencing the volume directly from a pod is not supported. #### Manually provisioning a Regional PD PersistentVolume Dynamic provisioning is possible using a [StorageClass for GCE PD](/docs/concepts/storage/storage-classes/#gce). Before creating a PersistentVolume, you must create the PD: ```shell gcloud beta compute disks create --size=500GB my-data-disk --region us-central1 --replica-zones us-central1-a,us-central1-b ``` Example PersistentVolume spec: ```yaml apiVersion: v1 kind: PersistentVolume metadata: name: test-volume labels: failure-domain.beta.kubernetes.io/zone: us-central1-a__us-central1-b spec: capacity: storage: 400Gi accessModes: - ReadWriteOnce gcePersistentDisk: pdName: my-data-disk fsType: ext4 ``` ### gitRepo (deprecated) {#gitrepo} {{< warning >}} **Warning:** The gitRepo volume type is deprecated. To provision a container with a git repo, mount an [EmptyDir](#emptydir) into an InitContainer that clones the repo using git, then mount the [EmptyDir](#emptydir) into the Pod's container. {{< /warning >}} A `gitRepo` volume is an example of what can be done as a volume plugin. It mounts an empty directory and clones a git repository into it for your Pod to use. In the future, such volumes may be moved to an even more decoupled model, rather than extending the Kubernetes API for every such use case. Here is an example for gitRepo volume: ```yaml apiVersion: v1 kind: Pod metadata: name: server spec: containers: - image: nginx name: nginx volumeMounts: - mountPath: /mypath name: git-volume volumes: - name: git-volume gitRepo: repository: "git@somewhere:me/my-git-repository.git" revision: "22f1d8406d464b0c0874075539c1f2e96c253775" ``` ### glusterfs {#glusterfs} A `glusterfs` volume allows a [Glusterfs](http://www.gluster.org) (an open source networked filesystem) volume to be mounted into your Pod. Unlike `emptyDir`, which is erased when a Pod is removed, the contents of a `glusterfs` volume are preserved and the volume is merely unmounted. This means that a glusterfs volume can be pre-populated with data, and that data can be "handed off" between Pods. GlusterFS can be mounted by multiple writers simultaneously. {{< caution >}} **Important:** You must have your own GlusterFS installation running before you can use it. {{< /caution >}} See the [GlusterFS example](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/glusterfs) for more details. ### hostPath {#hostpath} A `hostPath` volume mounts a file or directory from the host node's filesystem into your Pod. This is not something that most Pods will need, but it offers a powerful escape hatch for some applications. For example, some uses for a `hostPath` are: * running a Container that needs access to Docker internals; use a `hostPath` of `/var/lib/docker` * running cAdvisor in a Container; use a `hostPath` of `/sys` * allowing a Pod to specify whether a given `hostPath` should exist prior to the Pod running, whether it should be created, and what it should exist as In addition to the required `path` property, user can optionally specify a `type` for a `hostPath` volume. The supported values for field `type` are: | Value | Behavior | |:------|:---------| | | Empty string (default) is for backward compatibility, which means that no checks will be performed before mounting the hostPath volume. | | `DirectoryOrCreate` | If nothing exists at the given path, an empty directory will be created there as needed with permission set to 0755, having the same group and ownership with Kubelet. | | `Directory` | A directory must exist at the given path | | `FileOrCreate` | If nothing exists at the given path, an empty file will be created there as needed with permission set to 0644, having the same group and ownership with Kubelet. | | `File` | A file must exist at the given path | | `Socket` | A UNIX socket must exist at the given path | | `CharDevice` | A character device must exist at the given path | | `BlockDevice` | A block device must exist at the given path | Watch out when using this type of volume, because: * Pods with identical configuration (such as created from a podTemplate) may behave differently on different nodes due to different files on the nodes * when Kubernetes adds resource-aware scheduling, as is planned, it will not be able to account for resources used by a `hostPath` * the files or directories created on the underlying hosts are only writable by root. You either need to run your process as root in a [privileged Container](/docs/user-guide/security-context) or modify the file permissions on the host to be able to write to a `hostPath` volume #### Example Pod ```yaml apiVersion: v1 kind: Pod metadata: name: test-pd spec: containers: - image: k8s.gcr.io/test-webserver name: test-container volumeMounts: - mountPath: /test-pd name: test-volume volumes: - name: test-volume hostPath: # directory location on host path: /data # this field is optional type: Directory ``` ### iscsi {#iscsi} An `iscsi` volume allows an existing iSCSI (SCSI over IP) volume to be mounted into your Pod. Unlike `emptyDir`, which is erased when a Pod is removed, the contents of an `iscsi` volume are preserved and the volume is merely unmounted. This means that an iscsi volume can be pre-populated with data, and that data can be "handed off" between Pods. {{< caution >}} **Important:** You must have your own iSCSI server running with the volume created before you can use it. {{< /caution >}} A feature of iSCSI is that it can be mounted as read-only by multiple consumers simultaneously. This means that you can pre-populate a volume with your dataset and then serve it in parallel from as many Pods as you need. Unfortunately, iSCSI volumes can only be mounted by a single consumer in read-write mode - no simultaneous writers allowed. See the [iSCSI example](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/iscsi) for more details. ### local {#local} {{< feature-state for_k8s_version="v1.10" state="beta" >}} {{< note >}} **Note:** The alpha PersistentVolume NodeAffinity annotation has been deprecated and will be removed in a future release. Existing PersistentVolumes using this annotation must be updated by the user to use the new PersistentVolume `NodeAffinity` field. {{< /note >}} A `local` volume represents a mounted local storage device such as a disk, partition or directory. Local volumes can only be used as a statically created PersistentVolume. Dynamic provisioning is not supported yet. Compared to `hostPath` volumes, local volumes can be used in a durable and portable manner without manually scheduling Pods to nodes, as the system is aware of the volume's node constraints by looking at the node affinity on the PersistentVolume. However, local volumes are still subject to the availability of the underlying node and are not suitable for all applications. If a node becomes unhealthy, then the local volume will also become inaccessible, and a Pod using it will not be able to run. Applications using local volumes must be able to tolerate this reduced availability, as well as potential data loss, depending on the durability characteristics of the underlying disk. The following is an example PersistentVolume spec using a `local` volume and `nodeAffinity`: ```yaml apiVersion: v1 kind: PersistentVolume metadata: name: example-pv spec: capacity: storage: 100Gi # volumeMode field requires BlockVolume Alpha feature gate to be enabled. volumeMode: Filesystem accessModes: - ReadWriteOnce persistentVolumeReclaimPolicy: Delete storageClassName: local-storage local: path: /mnt/disks/ssd1 nodeAffinity: required: nodeSelectorTerms: - matchExpressions: - key: kubernetes.io/hostname operator: In values: - example-node ``` PersistentVolume `nodeAffinity` is required when using local volumes. It enables the Kubernetes scheduler to correctly schedule Pods using local volumes to the correct node. PersistentVolume `volumeMode` can now be set to "Block" (instead of the default value "Filesystem") to expose the local volume as a raw block device. The `volumeMode` field requires `BlockVolume` Alpha feature gate to be enabled. When using local volumes, it is recommended to create a StorageClass with `volumeBindingMode` set to `WaitForFirstConsumer`. See the [example](/docs/concepts/storage/storage-classes/#local). Delaying volume binding ensures that the PersistentVolumeClaim binding decision will also be evaluated with any other node constraints the Pod may have, such as node resource requirements, node selectors, Pod affinity, and Pod anti-affinity. An external static provisioner can be run separately for improved management of the local volume lifecycle. Note that this provisioner does not support dynamic provisioning yet. For an example on how to run an external local provisioner, see the [local volume provisioner user guide](https://github.com/kubernetes-incubator/external-storage/tree/master/local-volume). {{< note >}} **Note:** The local PersistentVolume requires manual cleanup and deletion by the user if the external static provisioner is not used to manage the volume lifecycle. {{< /note >}} ### nfs {#nfs} An `nfs` volume allows an existing NFS (Network File System) share to be mounted into your Pod. Unlike `emptyDir`, which is erased when a Pod is removed, the contents of an `nfs` volume are preserved and the volume is merely unmounted. This means that an NFS volume can be pre-populated with data, and that data can be "handed off" between Pods. NFS can be mounted by multiple writers simultaneously. {{< caution >}} **Important:** You must have your own NFS server running with the share exported before you can use it. {{< /caution >}} See the [NFS example](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/nfs) for more details. ### persistentVolumeClaim {#persistentvolumeclaim} A `persistentVolumeClaim` volume is used to mount a [PersistentVolume](/docs/concepts/storage/persistent-volumes/) into a Pod. PersistentVolumes are a way for users to "claim" durable storage (such as a GCE PersistentDisk or an iSCSI volume) without knowing the details of the particular cloud environment. See the [PersistentVolumes example](/docs/concepts/storage/persistent-volumes/) for more details. ### projected {#projected} A `projected` volume maps several existing volume sources into the same directory. Currently, the following types of volume sources can be projected: - [`secret`](#secret) - [`downwardAPI`](#downwardapi) - [`configMap`](#configmap) - `serviceAccountToken` All sources are required to be in the same namespace as the Pod. For more details, see the [all-in-one volume design document](https://github.com/kubernetes/community/blob/{{< param "githubbranch" >}}/contributors/design-proposals/node/all-in-one-volume.md). The projection of service account tokens is a feature introduced in Kubernetes 1.11. To enable this feature, you need to explicitly set the `TokenRequestProjection` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) to True. #### Example Pod with a secret, a downward API, and a configmap. ```yaml apiVersion: v1 kind: Pod metadata: name: volume-test spec: containers: - name: container-test image: busybox volumeMounts: - name: all-in-one mountPath: "/projected-volume" readOnly: true volumes: - name: all-in-one projected: sources: - secret: name: mysecret items: - key: username path: my-group/my-username - downwardAPI: items: - path: "labels" fieldRef: fieldPath: metadata.labels - path: "cpu_limit" resourceFieldRef: containerName: container-test resource: limits.cpu - configMap: name: myconfigmap items: - key: config path: my-group/my-config ``` #### Example Pod with multiple secrets with a non-default permission mode set. ```yaml apiVersion: v1 kind: Pod metadata: name: volume-test spec: containers: - name: container-test image: busybox volumeMounts: - name: all-in-one mountPath: "/projected-volume" readOnly: true volumes: - name: all-in-one projected: sources: - secret: name: mysecret items: - key: username path: my-group/my-username - secret: name: mysecret2 items: - key: password path: my-group/my-password mode: 511 ``` Each projected volume source is listed in the spec under `sources`. The parameters are nearly the same with two exceptions: * For secrets, the `secretName` field has been changed to `name` to be consistent with ConfigMap naming. * The `defaultMode` can only be specified at the projected level and not for each volume source. However, as illustrated above, you can explicitly set the `mode` for each individual projection. When the `TokenRequestProjection` feature is enabled, you can inject the token for the current [service account](/docs/reference/access-authn-authz/authentication/#service-account-tokens) into a Pod at a specified path. Below is an example: ```yaml apiVersion: v1 kind: Pod metadata: name: sa-token-test spec: containers: - name: container-test image: busybox volumeMounts: - name: token-vol mountPath: "/service-account" readOnly: true volumes: - name: token-vol projected: sources: - serviceAccountToken: audience: api expirationSeconds: 3600 path: token ``` The example Pod has a projected volume containing the injected service account token. This token can be used by Pod containers to access the Kubernetes API server, for example. The `audience` field contains the intended audience of the token. A recipient of the token must identify itself with an identifier specified in the audience of the token, and otherwise should reject the token. This field is optional and it defaults to the identifier of the API server. The `expirationSeconds` is the expected duration of validity of the service account token. It defaults to 1 hour and must be at least 10 minutes (600 seconds). An administrator can also limit its maximum value by specifying the `--service-account-max-token-expiration` option for the API server. The `path` field specifies a relative path to the mount point of the projected volume. {{< note >}} **Note:** A Container using a projected volume source as a [subPath](#using-subpath) volume mount will not receive updates for those volume sources. {{< /note >}} ### portworxVolume {#portworxvolume} A `portworxVolume` is an elastic block storage layer that runs hyperconverged with Kubernetes. Portworx fingerprints storage in a server, tiers based on capabilities, and aggregates capacity across multiple servers. Portworx runs in-guest in virtual machines or on bare metal Linux nodes. A `portworxVolume` can be dynamically created through Kubernetes or it can also be pre-provisioned and referenced inside a Kubernetes Pod. Here is an example Pod referencing a pre-provisioned PortworxVolume: ```yaml apiVersion: v1 kind: Pod metadata: name: test-portworx-volume-pod spec: containers: - image: k8s.gcr.io/test-webserver name: test-container volumeMounts: - mountPath: /mnt name: pxvol volumes: - name: pxvol # This Portworx volume must already exist. portworxVolume: volumeID: "pxvol" fsType: "" ``` {{< caution >}} **Important:** Make sure you have an existing PortworxVolume with name `pxvol` before using it in the Pod. {{< /caution >}} More details and examples can be found [here](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/portworx/README.md). ### quobyte {#quobyte} A `quobyte` volume allows an existing [Quobyte](http://www.quobyte.com) volume to be mounted into your Pod. {{< caution >}} **Important:** You must have your own Quobyte setup running with the volumes created before you can use it. {{< /caution >}} See the [Quobyte example](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/quobyte) for more details. ### rbd {#rbd} An `rbd` volume allows a [Rados Block Device](http://ceph.com/docs/master/rbd/rbd/) volume to be mounted into your Pod. Unlike `emptyDir`, which is erased when a Pod is removed, the contents of a `rbd` volume are preserved and the volume is merely unmounted. This means that a RBD volume can be pre-populated with data, and that data can be "handed off" between Pods. {{< caution >}} **Important:** You must have your own Ceph installation running before you can use RBD. {{< /caution >}} A feature of RBD is that it can be mounted as read-only by multiple consumers simultaneously. This means that you can pre-populate a volume with your dataset and then serve it in parallel from as many Pods as you need. Unfortunately, RBD volumes can only be mounted by a single consumer in read-write mode - no simultaneous writers allowed. See the [RBD example](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/rbd) for more details. ### scaleIO {#scaleio} ScaleIO is a software-based storage platform that can use existing hardware to create clusters of scalable shared block networked storage. The `scaleIO` volume plugin allows deployed Pods to access existing ScaleIO volumes (or it can dynamically provision new volumes for persistent volume claims, see [ScaleIO Persistent Volumes](/docs/concepts/storage/persistent-volumes/#scaleio)). {{< caution >}} **Important:** You must have an existing ScaleIO cluster already setup and running with the volumes created before you can use them. {{< /caution >}} The following is an example Pod configuration with ScaleIO: ```yaml apiVersion: v1 kind: Pod metadata: name: pod-0 spec: containers: - image: k8s.gcr.io/test-webserver name: pod-0 volumeMounts: - mountPath: /test-pd name: vol-0 volumes: - name: vol-0 scaleIO: gateway: https://localhost:443/api system: scaleio protectionDomain: sd0 storagePool: sp1 volumeName: vol-0 secretRef: name: sio-secret fsType: xfs ``` For further detail, please the see the [ScaleIO examples](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/staging/volumes/scaleio). ### secret {#secret} A `secret` volume is used to pass sensitive information, such as passwords, to Pods. You can store secrets in the Kubernetes API and mount them as files for use by Pods without coupling to Kubernetes directly. `secret` volumes are backed by tmpfs (a RAM-backed filesystem) so they are never written to non-volatile storage. {{< caution >}} **Important:** You must create a secret in the Kubernetes API before you can use it. {{< /caution >}} {{< note >}} **Note:** A Container using a Secret as a [subPath](#using-subpath) volume mount will not receive Secret updates. {{< /note >}} Secrets are described in more detail [here](/docs/user-guide/secrets). ### storageOS {#storageos} A `storageos` volume allows an existing [StorageOS](https://www.storageos.com) volume to be mounted into your Pod. StorageOS runs as a Container within your Kubernetes environment, making local or attached storage accessible from any node within the Kubernetes cluster. Data can be replicated to protect against node failure. Thin provisioning and compression can improve utilization and reduce cost. At its core, StorageOS provides block storage to Containers, accessible via a file system. The StorageOS Container requires 64-bit Linux and has no additional dependencies. A free developer license is available. {{< caution >}} **Important:** You must run the StorageOS Container on each node that wants to access StorageOS volumes or that will contribute storage capacity to the pool. For installation instructions, consult the [StorageOS documentation](https://docs.storageos.com). {{< /caution >}} ```yaml apiVersion: v1 kind: Pod metadata: labels: name: redis role: master name: test-storageos-redis spec: containers: - name: master image: kubernetes/redis:v1 env: - name: MASTER value: "true" ports: - containerPort: 6379 volumeMounts: - mountPath: /redis-master-data name: redis-data volumes: - name: redis-data storageos: # The `redis-vol01` volume must already exist within StorageOS in the `default` namespace. volumeName: redis-vol01 fsType: ext4 ``` For more information including Dynamic Provisioning and Persistent Volume Claims, please see the [StorageOS examples](https://github.com/kubernetes/examples/blob/master/staging/volumes/storageos). ### vsphereVolume {#vsphereVolume} {{< note >}} **Prerequisite:** Kubernetes with vSphere Cloud Provider configured. For cloudprovider configuration please refer [vSphere getting started guide](https://vmware.github.io/vsphere-storage-for-kubernetes/documentation/). {{< /note >}} A `vsphereVolume` is used to mount a vSphere VMDK Volume into your Pod. The contents of a volume are preserved when it is unmounted. It supports both VMFS and VSAN datastore. {{< caution >}} **Important:** You must create VMDK using one of the following method before using with Pod. {{< /caution >}} #### Creating a VMDK volume Choose one of the following methods to create a VMDK. {{< tabs name="tabs_volumes" >}} {{% tab name="Create using vmkfstools" %}} First ssh into ESX, then use the following command to create a VMDK: ```shell vmkfstools -c 2G /vmfs/volumes/DatastoreName/volumes/myDisk.vmdk ``` {{% /tab %}} {{% tab name="Create using vmware-vdiskmanager" %}} Use the following command to create a VMDK: ```shell vmware-vdiskmanager -c -t 0 -s 40GB -a lsilogic myDisk.vmdk ``` {{% /tab %}} {{< /tabs >}} #### vSphere VMDK Example configuration ```yaml apiVersion: v1 kind: Pod metadata: name: test-vmdk spec: containers: - image: k8s.gcr.io/test-webserver name: test-container volumeMounts: - mountPath: /test-vmdk name: test-volume volumes: - name: test-volume # This VMDK volume must already exist. vsphereVolume: volumePath: "[DatastoreName] volumes/myDisk" fsType: ext4 ``` More examples can be found [here](https://github.com/kubernetes/examples/tree/master/staging/volumes/vsphere). ## Using subPath Sometimes, it is useful to share one volume for multiple uses in a single Pod. The `volumeMounts.subPath` property can be used to specify a sub-path inside the referenced volume instead of its root. Here is an example of a Pod with a LAMP stack (Linux Apache Mysql PHP) using a single, shared volume. The HTML contents are mapped to its `html` folder, and the databases will be stored in its `mysql` folder: ```yaml apiVersion: v1 kind: Pod metadata: name: my-lamp-site spec: containers: - name: mysql image: mysql env: - name: MYSQL_ROOT_PASSWORD value: "rootpasswd" volumeMounts: - mountPath: /var/lib/mysql name: site-data subPath: mysql - name: php image: php:7.0-apache volumeMounts: - mountPath: /var/www/html name: site-data subPath: html volumes: - name: site-data persistentVolumeClaim: claimName: my-lamp-site-data ``` ### Using subPath with expanded environment variables {{< feature-state for_k8s_version="v1.11" state="alpha" >}} `subPath` directory names can also be constructed from Downward API environment variables. Before you use this feature, you must enable the `VolumeSubpathEnvExpansion`feature gate. In this example, a Pod uses `subPath` to create a directory `pod1` within the hostPath volume `/var/log/pods`, using the pod name from the Downward API. The host directory `/var/log/pods/pod1` is mounted at `/logs` in the container. ```yaml apiVersion: v1 kind: Pod metadata: name: pod1 spec: containers: - name: container1 env: - name: POD_NAME valueFrom: fieldRef: apiVersion: v1 fieldPath: metadata.name image: busybox command: [ "sh", "-c", "while [ true ]; do echo 'Hello'; sleep 10; done | tee -a /logs/hello.txt" ] volumeMounts: - name: workdir1 mountPath: /logs subPath: $(POD_NAME) restartPolicy: Never volumes: - name: workdir1 hostPath: path: /var/log/pods ``` ## Resources The storage media (Disk, SSD, etc.) of an `emptyDir` volume is determined by the medium of the filesystem holding the kubelet root dir (typically `/var/lib/kubelet`). There is no limit on how much space an `emptyDir` or `hostPath` volume can consume, and no isolation between Containers or between Pods. In the future, we expect that `emptyDir` and `hostPath` volumes will be able to request a certain amount of space using a [resource](/docs/user-guide/compute-resources) specification, and to select the type of media to use, for clusters that have several media types. ## Out-of-Tree Volume Plugins The Out-of-tree volume plugins include the Container Storage Interface (`CSI`) and `FlexVolume`. They enable storage vendors to create custom storage plugins without adding them to the Kubernetes repository. Before the introduction of `CSI` and `FlexVolume`, all volume plugins (like volume types listed above) were "in-tree" meaning they were built, linked, compiled, and shipped with the core Kubernetes binaries and extend the core Kubernetes API. This meant that adding a new storage system to Kubernetes (a volume plugin) required checking code into the core Kubernetes code repository. Both `CSI` and `FlexVolume` allow volume plugins to be developed independent of the Kubernetes code base, and deployed (installed) on Kubernetes clusters as extensions. For storage vendors looking to create an out-of-tree volume plugin, please refer to [this FAQ](https://github.com/kubernetes/community/blob/master/sig-storage/volume-plugin-faq.md). ### CSI {{< feature-state for_k8s_version="v1.10" state="beta" >}} [Container Storage Interface](https://github.com/container-storage-interface/spec/blob/master/spec.md) (CSI) defines a standard interface for container orchestration systems (like Kubernetes) to expose arbitrary storage systems to their container workloads. Please read the [CSI design proposal](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/storage/container-storage-interface.md) for more information. CSI support was introduced as alpha in Kubernetes v1.9 and moved to beta in Kubernetes v1.10. Once a CSI compatible volume driver is deployed on a Kubernetes cluster, users may use the `csi` volume type to attach, mount, etc. the volumes exposed by the CSI driver. The `csi` volume type does not support direct reference from Pod and may only be referenced in a Pod via a `PersistentVolumeClaim` object. The following fields are available to storage administrators to configure a CSI persistent volume: - `driver`: A string value that specifies the name of the volume driver to use. This value must correspond to the value returned in the `GetPluginInfoResponse` by the CSI driver as defined in the [CSI spec](https://github.com/container-storage-interface/spec/blob/master/spec.md#getplugininfo). It is used by Kubernetes to identify which CSI driver to call out to, and by CSI driver components to identify which PV objects belong to the CSI driver. - `volumeHandle`: A string value that uniquely identifies the volume. This value must correspond to the value returned in the `volume.id` field of the `CreateVolumeResponse` by the CSI driver as defined in the [CSI spec](https://github.com/container-storage-interface/spec/blob/master/spec.md#createvolume). The value is passed as `volume_id` on all calls to the CSI volume driver when referencing the volume. - `readOnly`: An optional boolean value indicating whether the volume is to be "ControllerPublished" (attached) as read only. Default is false. This value is passed to the CSI driver via the `readonly` field in the `ControllerPublishVolumeRequest`. - `fsType`: If the PV's `VolumeMode` is `Filesystem` then this field may be used to specify the filesystem that should be used to mount the volume. If the volume has not been formatted and formatting is supported, this value will be used to format the volume. If a value is not specified, `ext4` is assumed. This value is passed to the CSI driver via the `VolumeCapability` field of `ControllerPublishVolumeRequest`, `NodeStageVolumeRequest`, and `NodePublishVolumeRequest`. - `volumeAttributes`: A map of string to string that specifies static properties of a volume. This map must correspond to the map returned in the `volume.attributes` field of the `CreateVolumeResponse` by the CSI driver as defined in the [CSI spec](https://github.com/container-storage-interface/spec/blob/master/spec.md#createvolume). The map is passed to the CSI driver via the `volume_attributes` field in the `ControllerPublishVolumeRequest`, `NodeStageVolumeRequest`, and `NodePublishVolumeRequest`. - `controllerPublishSecretRef`: A reference to the secret object containing sensitive information to pass to the CSI driver to complete the CSI `ControllerPublishVolume` and `ControllerUnpublishVolume` calls. This field is optional, and may be empty if no secret is required. If the secret object contains more than one secret, all secrets are passed. - `nodeStageSecretRef`: A reference to the secret object containing sensitive information to pass to the CSI driver to complete the CSI `NodeStageVolume` call. This field is optional, and may be empty if no secret is required. If the secret object contains more than one secret, all secrets are passed. - `nodePublishSecretRef`: A reference to the secret object containing sensitive information to pass to the CSI driver to complete the CSI `NodePublishVolume` call. This field is optional, and may be empty if no secret is required. If the secret object contains more than one secret, all secrets are passed. #### CSI raw block volume support {{< feature-state for_k8s_version="v1.11" state="alpha" >}} Starting with version 1.11, CSI introduced support for raw block volumes, which relies on the raw block volume feature that was introduced in a previous version of Kubernetes. This feature will make it possible for vendors with external CSI drivers to implement raw block volumes support in Kubernetes workloads. CSI block volume support is feature-gated and turned off by default. To run CSI with block volume support enabled, a cluster administrator must enable the feature for each Kubernetes component using the following feature gate flags: ``` --feature-gates=BlockVolume=true,CSIBlockVolume=true ``` Learn how to [setup your PV/PVC with raw block volume support](/docs/concepts/storage/persistent-volumes/#raw-block-volume-support). ### FlexVolume `FlexVolume` is an out-of-tree plugin interface that has existed in Kubernetes since version 1.2 (before CSI). It uses an exec-based model to interface with drivers. FlexVolume driver binaries must be installed in a pre-defined volume plugin path on each node (and in some cases master). Pods interact with FlexVolume drivers through the `flexVolume` in-tree plugin. More details can be found [here](https://github.com/kubernetes/community/blob/master/contributors/devel/flexvolume.md). ## Mount propagation {{< feature-state for_k8s_version="v1.10" state="beta" >}} Mount propagation allows for sharing volumes mounted by a Container to other Containers in the same Pod, or even to other Pods on the same node. If the "`MountPropagation`" feature is disabled or a Pod does not explicitly specify specific mount propagation, volume mounts in the Pod's Containers are not propagated. That is, Containers run with `private` mount propagation as described in the [Linux kernel documentation](https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt). Mount propagation of a volume is controlled by `mountPropagation` field in Container.volumeMounts. Its values are: * `None` - This volume mount will not receive any subsequent mounts that are mounted to this volume or any of its subdirectories by the host. In similar fashion, no mounts created by the Container will be visible on the host. This is the default mode. This mode is equal to `private` mount propagation as described in the [Linux kernel documentation](https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt) * `HostToContainer` - This volume mount will receive all subsequent mounts that are mounted to this volume or any of its subdirectories. In other words, if the host mounts anything inside the volume mount, the Container will see it mounted there. Similarly, if any Pod with `Bidirectional` mount propagation to the same volume mounts anything there, the Container with `HostToContainer` mount propagation will see it. This mode is equal to `rslave` mount propagation as described in the [Linux kernel documentation](https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt) * `Bidirectional` - This volume mount behaves the same the `HostToContainer` mount. In addition, all volume mounts created by the Container will be propagated back to the host and to all Containers of all Pods that use the same volume. A typical use case for this mode is a Pod with a `FlexVolume` or `CSI` driver or a Pod that needs to mount something on the host using a `hostPath` volume. This mode is equal to `rshared` mount propagation as described in the [Linux kernel documentation](https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt) {{< caution >}} **Caution:** `Bidirectional` mount propagation can be dangerous. It can damage the host operating system and therefore it is allowed only in privileged Containers. Familiarity with Linux kernel behavior is strongly recommended. In addition, any volume mounts created by Containers in Pods must be destroyed (unmounted) by the Containers on termination. {{< /caution >}} ### Configuration Before mount propagation can work properly on some deployments (CoreOS, RedHat/Centos, Ubuntu) mount share must be configured correctly in Docker as shown below. Edit your Docker's `systemd` service file. Set `MountFlags` as follows: ```shell MountFlags=shared ``` Or, remove `MountFlags=slave` if present. Then restart the Docker daemon: ```shell $ sudo systemctl daemon-reload $ sudo systemctl restart docker ``` {{% capture whatsnext %}} * Follow an example of [deploying WordPress and MySQL with Persistent Volumes](/docs/tutorials/stateful-application/mysql-wordpress-persistent-volume/). {{% /capture %}}