Persistent Storage charts

These charts implement persistent storage that is within Kubernetes.

See the Kubernetes documentation for background material on how persistent storage works:

Using persistent storage is optional during development, but should be provisioned for and configured during production and realistic testing scenarios.

Local Directory

The local-directory chart creates local volumes on specific nodes, from directories. As there are no enforced limits for volume size and the node names are preconfigured, this chart is intended for use only for development and testing.

Multiple directories can be specified in the volumes list - an example is given in the values.yaml file of the chart. You should create another values file that is specific to your deployment that overrides these with the deployments node and directory names, and then ensure that these directories are created before running this chart.

The StorageClass created for all volumes created by this chart is local-directory.

There is an ansible playbook that automates the creation of directories on all the kubernetes nodes given a values file. Make sure that the inventory name in ansible matches the name of the host in the volumes list, then invoke with:

ansible-playbook -i <path to ansible inventory> --extra-vars "helm_values_file:<path to values.yaml>" local-directory-playbook.yaml

to create all local directories.

Then load the helm chart:

helm install -f <path to values.yaml> -n local-directory local-directory

You should then be able to list the local directory PV's:

$ kubectl get pv
large-pv   10Gi       RWO            Retain           Available             local-directory             8s
small-pv   2Gi        RWO            Retain           Available             local-directory             8s

Local Provisioner

The local-provisioner chart provides a local, non-distributed PersistentVolume that is usable on one specific node. It does this by running the k8s external storage local volume provisioner.

This type of storage is useful for workloads that have their own intrinsic HA or redundancy strategies, and only need storage on multiple nodes.

This provisioner is not "dynamic" in the sense that that it can't create a new PersistentVolume on demand from a storage pool, but the provisioner can automatically create volumes as disks/partitions are mounted on the nodes.

To create a new PV, a disk or partition on a node has to be formatted and mounted in specific locations, after which the provisioner will automatically create a PersistentVolume for the mount. As these volumes can't be split or resized, care must be taken to ensure that the correct quantity, types, and sizes of mounts are created for all the PersistentVolumeClaim's required to be bound for a specific workload.

By default, two StorageClasses were created to differentiate between Hard Disks and SSD's:

  • local-hdd, which offers PV's on volumes mounted in /mnt/local-storage/hdd/*
  • local-ssd, which offers PV's on volumes mounted in /mnt/local-storage/ssd/*

Adding a new local volume on a node

If you wanted to add a new volume to a node, you'd physically install a new disk in the system, then determine the device file it uses. Assuming that it's a hard disk and the device file is /dev/sdb, you might partition, format, and mount the disk like this:

$ sudo parted -s /dev/sdb \
    mklabel gpt \
    mkpart primary ext4 1MiB 100%
$ sudo mkfs.ext4 /dev/sdb1
$ echo "/dev/sdb1 /mnt/local-storage/hdd/sdb1 ext4 defaults 0 0" | sudo tee -a /etc/fstab
$ sudo mount /mnt/local-storage/hdd/sdb1

Then check that the PersistentVolume is created by the local-provisioner:

$ kubectl get pv
local-pv-2bfa2c43   19Gi       RWO            Delete           Available                          local-hdd                  6h

$ kubectl describe pv local-pv-
Name:              local-pv-2bfa2c43
Labels:            <none>
Finalizers:        []
StorageClass:      local-hdd
Status:            Available
Reclaim Policy:    Delete
Access Modes:      RWO
Capacity:          19Gi
Node Affinity:
  Required Terms:
    Term 0: in [node1]
    Type:  LocalVolume (a persistent volume backed by local storage on a node)
    Path:  /mnt/local-storage/hdd/sdb1
Events:    <none>

Ceph deployed with Rook

Rook provides an abstraction layer for Ceph and other distributed persistent data storage systems.

There are 3 Rook charts included with CORD:

  • rook-operator, which runs the volume provisioning portion of Rook (and is a thin wrapper around the upstream rook-ceph chart

  • rook-cluster, which defines the Ceph cluster and creates these StorageClass objects usable by other charts:

    • cord-ceph-rbd, dynamically create PersistentVolumes when a PersistentVolumeClaim is created. These volumes are only usable by a single container at a time.

    • cord-cephfs, a single shared filesystem which is mountable ReadWriteMulti on multiple containers via PersistentVolumeClaim. It's size is predetermined.

  • rook-tools, which provides a toolbox container for troubleshooting problems with Rook/Ceph

To create persistent volumes, you will need to load the first 2 charts, with the third only needed for troubleshooting and diagnostics.

Rook Node Prerequisties

By default, all the nodes running k8s are expected to have a directory named /mnt/ceph where the Ceph data is stored (the cephDataDir variable can be used to change this path).

In a production deployment, this would ideally be located on its own block storage device.

There should be at least 3 nodes with storage available to provide data redundancy.

Loading Rook Charts

First, add the rook-beta repo to helm, then load the rook-operator chart into the rook-ceph-system namespace:

helm repo add rook-beta
helm dep update rook-operator
helm install --namespace rook-ceph-system -n rook-operator rook-operator

Check that it's running (it will start the rook-ceph-agent and rook-discover DaemonSets):

$ kubectl -n rook-ceph-system get pods
NAME                                  READY     STATUS    RESTARTS   AGE
rook-ceph-agent-4c66b                 1/1       Running   0          6m
rook-ceph-agent-dsdsr                 1/1       Running   0          6m
rook-ceph-agent-gwjlk                 1/1       Running   0          6m
rook-ceph-operator-687b7bb6ff-vzjsl   1/1       Running   0          7m
rook-discover-9f87r                   1/1       Running   0          6m
rook-discover-lmhz9                   1/1       Running   0          6m
rook-discover-mxsr5                   1/1       Running   0          6m

Next, load the rook-cluster chart, which connects the storage on the nodes to the Ceph pool, and the CephFS filesystem:

helm install -n rook-cluster rook-cluster

Check that the cluster is running - this may take a few minutes, and look for the rook-ceph-mds-* containers to start:

$ kubectl -n rook-ceph get pods
NAME                                                  READY     STATUS      RESTARTS   AGE
rook-ceph-mds-cord-ceph-filesystem-7564b648cf-4wxzn   1/1       Running     0          1m
rook-ceph-mds-cord-ceph-filesystem-7564b648cf-rcvnx   1/1       Running     0          1m
rook-ceph-mgr-a-75654fb698-zqj67                      1/1       Running     0          5m
rook-ceph-mon0-v9d2t                                  1/1       Running     0          5m
rook-ceph-mon1-4sxgc                                  1/1       Running     0          5m
rook-ceph-mon2-6b6pj                                  1/1       Running     0          5m
rook-ceph-osd-id-0-85d887f76c-44w9d                   1/1       Running     0          4m
rook-ceph-osd-id-1-866fb5c684-lmxfp                   1/1       Running     0          4m
rook-ceph-osd-id-2-557dd69c5c-qdnmb                   1/1       Running     0          4m
rook-ceph-osd-prepare-node1-bfzzm                     0/1       Completed   0          4m
rook-ceph-osd-prepare-node2-dt4gx                     0/1       Completed   0          4m
rook-ceph-osd-prepare-node3-t5fnn                     0/1       Completed   0          4m

$ kubectl -n rook-ceph get storageclass
NAME            PROVISIONER                    AGE
cord-ceph-rbd             6m
cord-cephfs   6m

$ kubectl -n rook-ceph get filesystems
NAME                   AGE
cord-ceph-filesystem   6m

$ kubectl -n rook-ceph get pools
NAME             AGE
cord-ceph-pool   6m

$ kubectl -n rook-ceph get persistentvolume
cord-cephfs-pv      20Gi       RWX            Retain           Available             cord-cephfs              7m

At this point you can create a PersistentVolumeClaim on cord-ceph-rbd and a corresponding PersistentVolume will be created by the rook-ceph-operator acting as a volume provisioner and bound to the PVC.

Creating a PeristentVolumeClaim on cord-cephfs will mount the same CephFS filesystem on every container that requests it. The CephFS PV implementation currently isn't as mature as the Ceph RDB volumes, and may not remount properly when used with a PVC.

Troubleshooting Rook

Checking the rook-ceph-operator logs can be enlightening:

kubectl -n rook-ceph-system logs -f rook-ceph-operator-...

The Rook toolbox container has been containerized as the rook-tools chart, and provides a variety of tools for debugging Rook and Ceph.

Load the rook-tools chart:

helm install -n rook-tools rook-tools

Once the container is running (check with kubectl -n rook-ceph get pods), exec into it to run a shell to access all tools:

kubectl -n rook-ceph exec -it rook-ceph-tools bash

or run a one-off command:

kubectl -n rook-ceph exec rook-ceph-tools -- ceph status

or mount the CephFS volume:

kubectl -n rook-ceph exec -it rook-ceph-tools bash
mkdir /mnt/cephfs
mon_endpoints=$(grep mon_host /etc/ceph/ceph.conf | awk '{print $3}')
my_secret=$(grep key /etc/ceph/keyring | awk '{print $3}')
mount -t ceph -o name=admin,secret=$my_secret $mon_endpoints:/ /mnt/cephfs
ls /mnt/cephfs

Cleaning up after Rook

The rook-operator chart will leave a few DaemonSet behind after it's removed. Clean these up using these commands:

kubectl -n rook-ceph-system delete daemonset rook-ceph-agent
kubectl -n rook-ceph-system delete daemonset rook-discover
helm delete --purge rook-operator

If you have other charts that create PersistentVolumeClaims, you may need to clean them up manually (for example, if you've changed the StorageClass they use), list them with:

kubectl --all-namespaces get pvc

Files may be left behind in the Ceph storage directory and/or Rook configuration that need to be deleted before starting rook-* charts. If you've used the automation-tools/kubespray-installer scripts to set up a environment named test, you can delete all these files with the following commands:

cd cord/automation-tools/kubespray-installer
ansible -i inventories/test/inventory.cfg -b -m shell -a "rm -rf /var/lib/rook && rm -rf /mnt/ceph/*" all

The current upgrade process for Rook involves manual intervention and inspection using the tools container.

Using Persistent Storage

The general process for using persistent storage is to create a PersistentVolumeClaim on the appropriate StorageClass for the workload you're trying to run.

Example: XOS Database on a local directory

For development and testing, it may be useful to persist the XOS database.

First, configure your nodes to deploy the local-directory chart, then run:

If you haven't done it yet, add the CORD repository to the list of your local repositories and update the repo index:

helm repo add cord
helm repo update
helm install -f examples/xos-db-local-dir.yaml -n xos-core cord/xos-core

Example: XOS Database on a Ceph RBD volume

The XOS Database (Postgres) wants a volume that persists if a node goes down or is taken out of service, not shared with other containers running Postgres, thus the Ceph RBD volume is a reasonable choice to use with it.

Deploy the rook-operator and rook-cluster charts, then load the XOS core charts with:

helm install -f examples/xos-db-ceph-rbd.yaml -n xos-core cord/xos-core

Example: Docker Registry on CephFS shared filesystem

The Docker Registry wants a filesystem that is the shared across all containers, so it's a suitable workload for the cephfs shared filesystem.

Deploy the rook-operator and rook-cluster charts, then load the registry chart with:

helm install -f examples/registry-cephfs.yaml -n docker-registry stable/docker-registry

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