For the purposes of this guide, we’ll describe 「storage」 as a 「volume」 - a location on a disk where a user’s data resides.html
Kubernetes handles the creation and allocation of persistent volumes, under-the-hood it uses the cloud provider’s API to issue the proper commands. To that extent most of our discussion around volumes will describe Kubernetes objects.node
JupyterHub uses Kubernetes to manage user storage. There are two primary Kubernetes objects involved in allocating storage to pods:api
PersistentVolumeClaim
(PVC
) specifies what kind of storage is required. Its configuration is specified in your config.yaml
file.PersistentVolume
(PV
) is the actual volume where the user’s data resides. It is created by Kubernetes using details in a PVC
.As Kubernetes objects, they can be queried with the standard kubectl
commands (e.g., kubectl --namespace=<your-namespace> get pvc
)app
In JupyterHub, each user gets their own PersistentVolumeClaim
object, representing the data attached to their account. When a new user starts their JupyterHub server, a PersistentVolumeClaim
is created for that user. This claim tells Kubernetes what kind of storage (e.g., ssd vs. hd) as well as how much storage is needed. Kubernetes checks to see whether a PersistentVolume
object for that user exists (since this is a new user, none will exist). If no PV
object exists, then Kubernetes will use the PVC
to create a new PV
object for the user.less
Now that a PV
exists for the user, Kubernetes next must attach (or 「mount」) that PV
to the user’s pod (which runs user code). Once this is accomplished, the user will have access to their PV
within JupyterHub. Note that this all happens under-the-hood and automatically when a user logs in.ide
PersistentVolumeClaim
s and PersistentVolume
s are not deleted unless the PersistentVolumeClaim
is explicitly deleted by the JupyterHub administrator. When a user shuts down their server, their user pod is deleted and their volume is detached from the pod, but the PVC
and PV
objects still exist. In the future, when the user logs back in, JupyterHub will detect that the user has a pre-existing PVC
and will simply attach it to their new pod, rather than creating a new PVC
.ui
When Kubernetes uses the PVC
to create a new user PV
, it is sending a command to the underlying API of whatever cloud provider Kubernetes is running on. Occasionally, the request for a specific PV
might fail - for example, if your account has reached the limit in the amount of disk space available.this
Another common issue is limits on the number of volumes that may be simultaneously attached to a node in your cluster. Check your cloud provider for details on the limits of storage resources you request.google
Notespa
Some cloud providers have a limited number of disks that can be attached to each node. Since JupyterHub allocates one disk per user for persistent storage, this limits the number of users that can be running in a node at any point of time. If you need users to have persistent storage, and you end up hitting this limit, you must use more nodes in order to accommodate the disk for each user. In this case, we recommend allocating fewer resources per node (e.g. RAM) since you’ll have fewer users packed onto a single node.
Most configuration for storage is done at the cluster level and is not unique to JupyterHub. However, some bits are, and we will demonstrate here how to configure those.
Note that new PVC
s for pre-existing users will not be created unless the old ones are destroyed. If you update your users’ PVC
config via config.yaml
, then any new users will have the new PVC
created for them, but old users will not. To force an upgrade of the storage type for old users, you will need to manually delete their PVC
(e.g. kubectl --namespace=<your-namespace> delete pvc <pvc-name>
). This will delete all of the user’s data so we recommend backing up their filesystem first if you want to retain their data.
After you delete the user’s PVC
, upon their next log-in a new PVC
will be created for them according to your updated PVC
specification.
A StorageClass object is used to determine what kind of PersistentVolume
s are provisioned for your users. Most popular cloud providers have a StorageClass
marked as default. You can find out your default StorageClass
by doing:
kubectl get storageclass
and looking for the object with (default)
next to its name.
To change the kind of PersistentVolume
s provisioned for your users,
Create a new StorageClass
object following the kubernetes documentation
Specify the name of the StorageClass
you just created in config.yaml
singleuser: storage: dynamic: storageClass: <storageclass-name>
Do a helm upgrade
Note that this will only affect new users who are logging in. We recommend you do this before users start heavily using your cluster.
We will provide examples for popular cloud providers here, but will generally defer to the Kubernetes documentation.
On Google Cloud, the default StorageClass
will provision Standard Google Persistent Disks. These run on Hard Disks. For more performance, you may want to use SSDs. To use SSDs, you can create a new StorageClass
by first putting the following yaml
into a new file. We recommend a descriptive name such as storageclass.yaml
, which we’ll use below:
kind: StorageClass apiVersion: storage.k8s.io/v1 metadata: name: jupyterhub-user-ssd provisioner: kubernetes.io/gce-pd parameters: type: pd-ssd zones: <your-cluster-zone>
Replace <your-cluster-zone>
with the Zone in which you created your cluster (you can find this with gcloud container clusters list
).
Next, create this object by running kubectl apply -f storageclass.yaml
from the commandline. The Kubernetes Docs have more information on what the various fields mean. The most important field is parameters.type
, which specifies the type of storage you wish to use. The two options are:
pd-ssd
makes StorageClass
provision SSDs.pd-standard
will provision non-SSD disks.Once you have created this StorageClass
, you can configure your JupyterHub’s PVC
template with the following in your config.yaml
:
singleuser: storage: dynamic: storageClass: jupyterhub-user-ssd
Note that for storageClass:
we use the name that we specified above in metadata.name
.
You can set the size of storage requested by JupyterHub in the PVC
in your config.yaml
.
storage: capacity: 2Gi
This will request a 2Gi
volume per user. The default requests a 10Gi
volume per user.
We recommend you use the IEC Prefixes (Ki, Mi, Gi, etc) for specifying how much storage you want. 2Gi
(IEC Prefix) is (2 * 1024 * 1024 * 1024)
bytes, while 2G
(SI Prefix) is (2 * 1000 * 1000 * 1000)
bytes.
If you do not wish for users to have any persistent storage, it can be turned off. Edit the config.yaml
file and set the storage type to none
:
singleuser: storage: type: none
Next apply the changes.
After the changes are applied, new users will no longer be allocated a persistent $HOME
directory. Any currently running users will still have access to their storage until their server is restarted. You might have to manually delete current users’ PVCs
with kubectl
to reclaim any cloud disks that might have allocated. You can get a current list of PVC
s with:
kubectl --namespace=<your-namespace> get pvc
You can then delete the PVCs
you do not want with:
kubectl --namespace=<your-namespace> delete pvc <pvc-name>
Remember that deleting someone’s PVC
s will delete all their data, so do so with caution!