4. Using ROBIN CNS in Kubernetes

The Container Storage Interface (CSI) is a standard for exposing storage to workloads on Kubernetes. To enable automatic creation/deletion of volumes for CSI Storage, a Kubernetes resource called StorageClass must be created and registered within the Kubernetes cluster. Associated with the StorageClass is a CSI provisioner plugin that does the heavy lifting at disk and storage management layers to provision storage volumes based on the various attributes defined in the StorageClass. Kubernetes CSI was introduced in Kubernetes v1.9 release, promoted to beta in Kuberentes v1.10 release as CSI v0.3, followed by a GA release in Kubernetes v1.13 as CSI v1.0.

ROBIN ships with StorageClasses as below:

1. robin - The StorageClass that is default and will not have any feature enabled and can be used for standard RWO/RWX volumes

2. robin-repl-3 - The StorageClass for volume needing 3 replicas with fault domain as ‘Host’

3. robin-immediate - The StorageClass that will create volume as soon as PVC is created and will not wait for the first consumer of that volume.

All storage classes follow the same parameters as described below. All parameters are optional so enable or remove it as per the requirements.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
    name: <"storage-class-name">
provisioner: robin
reclaimPolicy: Delete
parameters:
    media: <SSD, HDD>
    blocksize: <"512", "4096">
    fstype: <ext4, xfs>
    replication: <"2", "3">
    faultdomain: <disk, host>
    compression: <LZ4>
    encryption: <CHACHA20, AES256, AES128>
    workload: <ordinary, throughput, latency, dedicated>
    snapshot_space_limit: <"50">
    rpool: <"default">

media	The media type ROBIN should use to allocate PersistentVolumes. Two values are supported: HDD for spinning-disks and SSD for Solid State Devices. ROBIN automatically discovers the media type of the underlying local disks. If not provided ROBIN will choose type of the first discovered media. For example, GCE Standard Persistent Disk is treated as HDD media type and GCE SSD Persistent Disk is treated as an SSD media type.
blocksize	By default ROBIN uses 4096 as the block size of the underlying logical block device it creates. You can overwrite it by setting it to 512 for certain workloads that require it.
fstype	By default the logical block device created by ROBIN is formatted using ext4 filesystem. It can also be changed to xfs
replication	By default ROBIN does not enable replication for the logical block device. It can be set to ‘2’ or ‘3’ to setup 2-way or 3-way replication. Robin implements a strictly consistent data replication guarantee. Which means that a write IO is NOT acknowledged back to the client until it is made durable on all replicas.
faultdomain	The fault domain to be used when “replication” is turned on. Setting the right fault domain maximizes data safety. Setting it to disk results in ensuring that Robin picks two different disks to keep the replication copies. ROBIN also tries to pick disks on different nodes to ensure higher availability in the event of node failures. But on a very busy cluster, if there are no spare disks on different nodes, setting the fault domain to disk would result in disks from the same node to be picked up for storing the replicated copies of the volume. To prevent this and to ensure that your application can tolerate entire node going down, you can set the fault domain to host. Doing so would gurantee that ROBIN never picks disks from the same node when storing replicated data of a volume. If disks across different nodes are not available, then the volume creation is failed rather than degrading to disk level fault domain. The default value is disk.
compression	By default inline data compression is disabled. It can be enabled by setting it to LZ4 which turns on inline block-level data compression using LZ4 compression algorithm. Support for other compression algorithms is on the roadmap
encryption	By default data-at-rest encryption is not enabled. To enable it set it to CHACHA20, AES128 or AES256, which uses one of these algorithms to perform block-level encryption of data for that PersistentVolume.
workload	throughput : If a volume has high throughput requirements this workload type can be used. Typically these are volumes that are used for large stream of IOs such as data volumes. Robin allocates no more than 1 such volumes per device. This type of volume can share the device with other ordinary volumes. latency : If a volume has low latency requirements this workload type can be used. Typically these are volumes that are used for heart beats. The amount of data written is small, but the IO has to complete within strict time limits. By default ROBIN allocates no more than 2 such volumes per device. This type of volumes can share device along with other ordinary volumes. dedicated : The entire device is dedicated to a volume when this workload type is used. This ensures that the volume gets all the IO bandwidth offered by the device. No other volume can share the device. ordinary : All other volumes that are not classified as any of the above are given this workload type. Any number of ordinary volumes can share the same device.
snapshot_space_limit	This is how much space that is set aside for snapshots for this volume. For example, if volume size is 100GB, value of “30” here would be 30GB space reserved for snapshots. New snapshot creation will fail once this limit is reached. Default is 40% of volume size.
rpool	Resource pools are a construct in Robin which allow you to group nodes in the cluster together for allocation purposes. Pools provide resource isolation. The default resource pool is default

Note

Make sure that for blocksize and replication, the values are passed as quoted strings to adhere to CSI spec. That is, blocksize should be passed as “4096” (quoted) and NOT as 4096 (unquoted)

4.1. Using Robin CNS Storage Class to Provision Storage

4.1.1. Basic Use Case

• Creating a PVC with Robin CNS StorageClass:

  First configure YAML similar to the one shown below for a PersistentVolumeClaim (PVC) using the Robin CNS StorageClass.

  apiVersion: v1
  kind: PersistentVolumeClaim
  metadata:
     name: mypvc
  
  spec:
     accessModes:
         - ReadWriteOnce
     resources:
         requests:
            storage: 10Gi
     storageClassName: robin
  

  Run the following command to create the PVC defined in above yaml:

  $ kubectl create -f mypvc.yaml
  persistentvolumeclaim/mypvc created
  

  Note

  Notice that under metadata/annotations we have spcified the storage class as storageClassName: robin. This results in the ROBIN CNS Storage Class to be be picked up.

  Verify the desired PVC exists and was created successfully by running the following command:

  $ kubectl get pvc
  NAME                        STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
  mypvc                       Pending                                                                        robin          7s
  

• Attach the PersistentVolumeClaim to a simple Pod:

  Configure a Pod YAML, similar to the one showcased below, wherein which the volume we created previously is referenced.

  kind: Pod
  apiVersion: v1
  metadata:
      name: myweb
  spec:
      volumes:
        - name: htdocs
          persistentVolumeClaim:
            claimName: mypvc
      containers:
        - name: myweb0
          image: nginx
          ports:
              - containerPort: 80
                name: "http-server"
          volumeMounts:
              - mountPath: "/usr/share/nginx/html"
                name: htdocs
  

  Run the following command to actually create the Pod:

  $ kubectl create -f mypod.yaml
  

  We can confirm that the PersistentVolumeClaim is bound to the pod and a PersistantVolume is created by issuing the following commands:

  $ kubectl get pvc
  NAME                        STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
  mypvc                       Bound    pvc-7a18d80c-6c26-4585-a949-24d9005e3d7f   10Gi       RWO            robin          6m1s
  
  $ kubectl get pv
  NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                               STORAGECLASS   REASON   AGE
  pvc-7a18d80c-6c26-4585-a949-24d9005e3d7f   10Gi       RWO            Delete           Bound    default/mypvc                       robin                   5m32s
  

4.1.2. Customizing Volume Provisioning

Let’s say that we’d like to create a PVC which meets the following requirements:

• Data is replicated 3-ways

• The Pod should continue to have access to data even if 2 of the 3 disks or the nodes on which these disks are hosted go down

• The data must be compressed

• The data should only reside on SSD media

This is accomplished by specifying these requirements under metadata/annotations section of the PVC Spec as described in the YAML below. Please notice that each annotations are prefixed with robin.io/. Except fstype, Annotations can take exact same parameters as in ROBIN CNS Storage Class YAML detailed above and would override the corresponding parameters specified in the StorageClass.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
   name: proteced-compressed-pvc
   annotations:
      robin.io/replication: "3"
      robin.io/faultdomain: host
      robin.io/compression: LZ4
      robin.io/media: SSD

spec:
   accessModes:
       - ReadWriteOnce
   resources:
       requests:
          storage: 1Gi
   storageClassName: robin

Run the following command to create the PVC:

$ kubectl create -f newpvc.yaml
persistentvolumeclaim/proteced-compressed-pvc created

$ kubectl get pvc
NAME                        STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
mypvc                       Bound     pvc-7a18d80c-6c26-4585-a949-24d9005e3d7f   10Gi       RWO            robin          62m
proteced-compressed-pvc     Pending                                                                        robin          47s

Note

Note that the number 3 is quoted as “3” when specifying the robin.io/replication: annotation. This is per the Kubernetes Spec. Not doing so would result in an error being thrown by Kuberentes

4.1.3. Using ROBIN CNS in a StatefulSet

In a StatefulSet a PVC is not directly referenced as in the above examples, but instead a volumeClaimTemplate is used to describe the type of PVC that needs to be created as part of the creation of the StatefulSet resource. This is accomplished via the following YAML:

apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
      app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: k8s.gcr.io/nginx-slim:0.8
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
      annotations:
        robin.io/replication: "2"
        robin.io/media: SSD
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi
      storageClassName: robin

The following commands can be used to create the Statefulset and ensure the correct PVCs are used:

$ kubectl create -f myweb.yaml
service/nginx created
statefulset.apps/web created


$ kubectl get statefulset
NAME   READY   AGE
web    2/2     12s

$ kubectl get pvc
NAME        STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
www-web-0   Bound    pvc-2b97d8fc-479d-11e9-bac1-00155d61160d   1Gi        RWO            robin          8s
www-web-1   Bound    pvc-436536e6-479d-11e9-bac1-00155d61160d   1Gi        RWO            robin          8s

$ kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM               STORAGECLASS   REASON   AGE
pvc-2b97d8fc-479d-11e9-bac1-00155d61160d   1Gi        RWO            Delete           Bound    default/www-web-0   robin                   10s
pvc-436536e6-479d-11e9-bac1-00155d61160d   1Gi        RWO            Delete           Bound    default/www-web-1   robin                   10s

4.1.4. Provisioning Storage for Helm Charts

Helm charts are a popular way to deploy an entire stack of Kubernetes resources in one shot. A helm chart is installed using helm install command. To use Robin CNS for persistent storage one needs to pass it as --set persistence.storageClass=robin command line option as shown below:

$ helm install --name pgsqldb stable/mysql --set persistence.storageClass=robin

This would result in Robin being used as the storage provisioner for PersistentVolumeClaims created by this helm chart.

4.2. Protecting PVCs using ROBIN’s Volume Replication

Robin uses storage volume-level replication to ensure that data is always available in the event of nodes and disk failures. When replication is configured to 2, at least 2 copies of the volume on maintained on different disks, if set to 3 at least 3 copies are maintained. This ensures that the volume’s data is available in the event of 1 or 2 disk/node failures. Configuring replication is done by annotating the PVC spec with robin.io/replication: "<count>" and optionally robin.io/faultdomain: disk|host|rack as shown in the YAML below:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
   name: replicated-pvc
   annotations:
      robin.io/replication: "3"
      robin.io/faultdomain: host

spec:
   accessModes:
       - ReadWriteOnce
   resources:
       requests:
          storage: 1Gi
   storageClassName: robin

Setting the correct value for robin.io/fautdomain to either disk or host or rack ensures that this PVC’s data is available in the event of just a disk or also node failures.

How are faults handled?

ROBIN uses strict-consistency semantics to guarantee correctness for your mission critical stateful applications. Which means that a “write” IO is not ackowledged back to the application until it has been made durable on all the healthy replicas disks. It is possible that one or more replica disks for a volume can go down for short periods of time (node going through a reboot cycle), or for longer periods of time (node has a hardware fault and can’t be brought online unti the part is replaced). ROBIN handles both cases gracefully. When a replica disk becomes available during IO, ROBIN automatically evicts it from the replication group. IOs continue to go to the remaining healthy replicas. When the faulted disks becomes available ROBIN automatically brings it up to the same state as the other healthy disks before adding it back into the replication group. This is automatically handled and transparent to the application.

When a disk suffers a more serious error. For example, an IO error is returned by the disk during a write or read operation. In this case ROBIN marks that disk as faulted and generates an alert for the storage admin to investigate. The storage admin can then determine the nature of the error and then mark that disk as healthy, in which case ROBIN adds it back into the replication group and initiates a data resync to bring it up to the same level as the other healthy disks. If the error is serious (e.g., SMART counters returns corruption), or if the node has a motherboard or IO card fault that needs to be replaced, the storage admin can permanently decommison that disk or node from the Kubernetes cluster. Doing so would also automatically evict that disk from the replication group of the PVC. The storage admin can then add a new healthy disk to the replication group so that the PVC can be brought back to the same level of availability as before.

There is a practical reason why ROBIN doesn’t automatically trigger rebuilds of fauluted disks. ROBIN is currently being used in mission critical workloads with multiple-petabytes under management by the ROBIN storage stack. We have seen scenarios where an IO controller card has failed while it has 12 disks of 10TiB each. That is 120 TiB of storage capacity under a single IO controller card. Rebuilding 120 TiB of data takes more time than replacing a faulted IO controller card with a healthy one. Also, moving 120 TiB of data over the network from healthy disks on other nodes puts a significant load on the network switches and the applications running on the nodes from which the data is pulled. This results in noticeable performance deradation. With our experience managing storage under large scale deployments and taking feedback from admins managing those cluters we have determined that it is best to inform an admin of a failure and let them decide, based on cost and time, wheather they want to replace a faulty hardware or want ROBIN to initiate a rebuild.

4.3. Making Robin the default StorageClass

To avoid typing the name of the StorageClass each time a new chart is deployed, it is highly recommend to set Robin’s StorageClass as the default Kubernetes StorageClass. This can be done as follows:

• Check for the current default StorageClass:

  Inspect if there is already a different StorageClass marked as default by running the following command:

  $ kubectl get storageclass
  NAME            PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
  gp2 (default)   kubernetes.io/aws-ebs   Delete          WaitForFirstConsumer   true                   8d
  robin           robin                   Delete          WaitForFirstConsumer   true                   5d5h
  

• Set the non-Robin StorageClass as “non-default”:

  In order to mark the current default StorageClass as “non-default” run the following command:

  $ kubectl patch storageclass gp2 \
     -p '{"metadata": {"annotations":{"storageclass.beta.kubernetes.io/is-default-class":"false"}}}'
  

  Note

  Before patching the storage class ensure that the annotation specified is correct. The above example is specific to a GKE cluster running version 1.12 of Kubernetes.

• Mark Robin as the new default StorageClass:

  To set the Robin CNS native StorageClass as the default for the cluster, run the following command:

  $ kubectl patch storageclass robin \
    -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"true"}}}'
  

  Note

  Before patching the ROBIN storage class ensure that name specified is correct as for Kubernetes versions newer than 1.13 it appears as robin but for older versions it is displayed as robin-0-3

• Verify that Robin is now the default StorageClass:

  Issue the following command to confirm that Robin is now the default StorageClass:

  $ kubectl get storageclass
  NAME              PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
  gp2               kubernetes.io/aws-ebs   Delete          WaitForFirstConsumer   true                   8d
  robin (default)   robin                   Delete          WaitForFirstConsumer   true                   5d5h
  

To learn more see official documentation on how to Change the default StorageClass.

4.4. ReadWriteMany (RWX) Volumes

Robin supports the ReadWriteMany (RWX) access mode of Persistent Volumes (PVs). An RWX PVC can be used by many Pods in the same namespace for read and write operations. For more information, see Persistent Volumes.

Robin RWX volumes are based on the shared file system. The shared file system that Robin uses is the network file system (NFS).

Note

• Robin RWX PVC supports only helm deployment, not bundle deployment.

• Robin RWX PVC supports non-root application Pods. For more information, see here.

4.4.1. NFS server Pod

Every RWX PVC results in an NFS export from an NFS server Pod. When you create a PVC, the NFS server Pod is created based on the demand and the configuration of NFS server creation.

Note

All Robin NFS server Pods are High Availability (HA) compliant. Robin monitors the health of the NFS server Pods and executes a failover if any NFS server Pod is offline.

There are two types of NFS server Pod.

• Shared NFS server Pod

• Exclusive NFS server Pod

• Shared NFS server Pod

In a shared NFS server Pod, multiple RWX PVC exports are allocated to one NFS server Pod. The shared NFS server Pod is the default server Pod for Robin RWX PVC.

Set the default server type to a shared NFS server Pod

To set the default_server_type to a shared NFS server Pod, run the following command:

# robin config update nfs default_server_type shared

Allocate the shared NFS server Pod for PVC

To allocate the shared NFS server Pod for the PVC, use the following annotation:

robin.io/nfs-server-type: "shared"

Example

To create a shared NFS server Pod which exports 1G RWX PVC.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nfs-shared-1
  annotations:
   robin.io/nfs-server-type: "shared"
spec:
  accessModes:
     - ReadWriteMany
  resources:
    requests:
      storage: 1Gi

• Exclusive NFS server Pod

In an exclusive NFS server Pod, each RWX PVC results in a dedicated NFS server Pod.

Set the default server type to an exclusive NFS server Pod

To set the default_server_type to an exclusive NFS server Pod, run the following command:

# robin config update nfs default_server_type exclusive

Allocate the exclusive NFS server Pod for PVC

To allocate the exclusive NFS server Pod for the PVC, use the following annotation:

robin.io/nfs-server-type: "exclusive"

Example

To create an exclusive NFS server Pod which exports 1G RWX PVC.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nfs-excl-1
  annotations:
   robin.io/nfs-server-type: "exclusive"
spec:
  accessModes:
     - ReadWriteMany
  resources:
    requests:
      storage: 1Gi

4.4.2. Set resource limits for RWX PVC

You can set maximum and request limits for CPU and memory only for the exclusive NFS server Pods with RWX volume through the following PVC annotations.

Set limits for CPU

To set the maximum limit for CPU, use the following annotation:

robin.io/nfs-cpu-limit: <limit value>

To set the request limit for CPU, use the following annotation:

robin.io/nfs-cpu-request: <request value>

Set limits for memory

To set the maximum limit for memory, use the following annotation:

robin.io/nfs-memory-limit: <limit value>

To set the request limit for memory, use the following annotation:

robin.io/nfs-memory-request: <request value>

Example

To create an exclusive NFS server Pod with PVC annotations which exports 1G RWX PVC.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: CSI-PVC-robin
  labels:
    app.kubernetes.io/instance: robin
    app.kubernetes.io/managed-by: robin.io
    app.kubernetes.io/name: robin
  annotations:
    robin.io/media: HDD
    robin.io/compression: LZ4
    robin.io/nfs-server-type: "exclusive"
    robin.io/nfs-cpu-limit: 300m
    robin.io/nfs-memory-limit: 300Mi
    robin.io/nfs-cpu-request: 240m
    robin.io/nfs-memory-request: 240Mi
spec:
  accessModes:
     - ReadWriteMany
  resources:
    requests:
      storage: 1Gi
  StorageClassName: robin

Note

• The PVC annotations override the global default value.

• You can use these PVC annotations only when you are creating a new PVC.

4.4.3. Configure NFS server Pod attributes

If you want to create an NFS server Pod other than the default configuration, you can change the NFS server Pod attributes.

The modified values are applied only to the next NFS server Pod creation. These values are not applied to the existing NFS server Pods.

View NFS server Pod attributes and values

To view the list of NFS server Pod attributes and their values, run the following command:

# robin config list nfs

NFS server Pod attributes and their values

Attribute	Default Value	Valid Value
default_server_type	shared	shared - multiple RWX PVC exports are allocated to one NFS server Pod. exclusive - each RWX PVC results in a dedicated NFS server Pod.
excl_pod_cpu	100m	As per your requirement.
excl_pod_memory	200Mi	As per your requirement.
exclusive_pod_cpu_limit	UNLIMITED	As per your requirement.
exclusive_pod_memory_limit	UNLIMITED	As per your requirement.
failover_enabled	1	1 – to enable the failover. 0 – to disable the failover.
max_exports_per_pod	8	As per your requirement.
nfs_server_storage_affinity	none	none - an NFS server Pod is created on a node where sufficient storage and other resources are available, without checking for allocated volume. preferred - an NFS server Pod is created on the same node as the volume is allocated. If no sufficient storage and other resources are available on the node, the NFS server Pod is created on the available node. required - an NFS server Pod is created on the same node as the volume is allocated. If no sufficient storage and other resources are available on the node, the NFS server Pod creation fails.
pod_creation_timeout	600	As per your requirement.
service_creation_timeout	60	As per your requirement.
shared_pod_cpu	100m	As per your requirement.
shared_pod_cpu_limit	UNLIMITED	As per your requirement.
shared_pod_failover_serialized	1	1 – to enable the shared Pod failover. 0 – to disable the shared Pod failover.
shared_pod_memory	200Mi	As per your requirement.
shared_pod_memory_limit	UNLIMITED	As per your requirement.
shared_pod_placement	PACK	PACK – selects the NFS server Pod that is assigned to the most and under the max limit. SPREAD – selects the NFS server Pod with minimum PVC assignments and ensures that all NFS server Pods are equally loaded.

Update the NFS server Pod attributes

To update the NFS server Pod attributes, run the following command:

# robin config update nfs <attribute> <valid value>

Example

To update the shared_pod_placement attribute of the NFS server Pod.

# robin config update nfs shared_pod_placement SPREAD
The 'nfs' attribute 'shared_pod_placement' has been updated

4.5. Robin StorageClass with GID and UID to Run Non-Root App Pods

In Kubernetes, only the root user can access all the persistent volumes. However, using new parameters in Robin’s StorageClass, you can allow a specific set of users to access the persistent volume. You can provide read and write access for a non-root user to a persistent volume by providing GID and UID when creating a new Robin StorageClass. Use this StorageClass in the PVC and set Pod’s security context with the runAsUser value. When you provide a GID for read and write access to the persistent volumes, any non-root user that belongs to the group ID, including a Pod, is granted access to the file storage.

The following is the sample YAML file:

allowVolumeExpansion: true
apiVersion: storage.k8s.io/v1
kind: StorageClass
labels:
  app.kubernetes.io/instance: robin
  app.kubernetes.io/managed-by: robin.io
  app.kubernetes.io/name: robin
metadata:
        name: robin-gid
parameters:
  gidAllocate: "true"
  gidFixed: "1001"
  media: HDD
  uidFixed: "1001"
provisioner: robin
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer

Note

There are Kubernetes known permission issues when you mount a volume with subPath for non-root users. As a workaround, you can remove the subPath parameter or use init container to chown the path. For details about the known issue, see here.

4.6. Snapshot Volumes

Just like storage management, which is done by an external storage provisioner such as Robin, taking snapshots of a volume is also done using a Snapshoting provisioner that is registered with Kubernetes. See more details on the official documentation on Volume Snapshots. Robin supports Kubernetes snapshots for Kubernetes versions v1.13 and beyond.

• Register a SnapshotClass with Kubernetes:

  First configure an appropriate YAML (an example is given below) representing the SnapshotClass.

  apiVersion: snapshot.storage.k8s.io/v1beta1
  kind: VolumeSnapshotClass
  metadata:
    name: robin-snapshotclass
    labels:
      app.kubernetes.io/instance: robin
      app.kubernetes.io/managed-by: robin.io
      app.kubernetes.io/name: robin
  driver: robin
  deletionPolicy: Delete
  

  Create the SnapshotClass by running the following command:

  $ kubectl create -f csi-robin-snapshotclass.yaml
  volumesnapshotclass.snapshot.storage.k8s.io/robin-snapshotclass created
  

  Moreover confirm that a SnapshotClass is registered via the following command:

  $ kubectl get volumesnapshotclass
  NAME                  DRIVER   DELETIONPOLICY   AGE
  robin-snapshotclass   robin    Delete           18s
  

• Take a snapshot of a PersistentVolumeClaim:

  In order to actually take a snapshot of PVC, first configure a YAML with the name of the SnapshotClass and the PVC that needs to be snapshotted like below.

  apiVersion: snapshot.storage.k8s.io/v1beta1
  kind: VolumeSnapshot
  metadata:
    name: snapshot-mypvc
    labels:
      app.kubernetes.io/instance: robin
      app.kubernetes.io/managed-by: robin.io
      app.kubernetes.io/name: robin
  spec:
    volumeSnapshotClassName: robin-snapshotclass
    source:
      persistentVolumeClaimName: mypvc
  

  Run the following command to actually create the snapshot:

  $ kubectl create -f take-snapshot.yaml
  volumesnapshot.snapshot.storage.k8s.io/snapshot-mypvc created
  

  Lastly verify that the VolumeSnapshot for the PersistentVolumeClaim is created with the following command:

  $ kubectl get volumesnapshot
  NAME                 READYTOUSE   SOURCEPVC   SOURCESNAPSHOTCONTENT   RESTORESIZE   SNAPSHOTCLASS         SNAPSHOTCONTENT                                    CREATIONTIME   AGE
  snapshot-mypvc       false        mypvc                                             robin-snapshotclass   snapcontent-06c17c2b-e7bb-4dc9-86df-e5fd05821977                  4m28s
  
  
  $ kubectl get volumesnapshotcontent
  NAME                                               READYTOUSE   RESTORESIZE   DELETIONPOLICY   DRIVER   VOLUMESNAPSHOTCLASS   VOLUMESNAPSHOT       AGE
  snapcontent-06c17c2b-e7bb-4dc9-86df-e5fd05821977                              Delete           robin    robin-snapshotclass   snapshot-mypvc       41s
  

4.7. Clone Volumes

Robin has the capability of creating a clone from a snapshot of a volume. We allow users to have RW clone so that old data can be read from parent snapshot and new data can be overwritten on the newly provisioned cloned volume. See more details on the official Kubernetes documentation on Volume Snapshot Restores and Clones. ROBIN supports Kubernetes Clones for Kubernetes v1.13 and beyond.

Note

The clone functionality is still an Alpha feature in Kubernetes so it requires VolumeSnapshotDataSource feature gate be enabled on the apiserver and controller-manager. More documentation on how to enable the feature can be found here.

• Clone a VolumeSnapshot:

  Configure a YAML as below in order to clone a VolumeSnapshot.

  Note

  All robin.io annotations showcased below refer to the same options described in the Robin CNS StorageClass YAML.

  apiVersion: v1
  kind: PersistentVolumeClaim
  metadata:
    name: mypvc-clone-snap1
  #annotations:
    # robin.io/media: <SSD, HDD>
    # robin.io/replication: <"2", "3">
    # robin.io/faultdomain: <disk, host>          // default disk
    # robin.io/encryption: <CHACHA20, AES256, AES128>
    # robin.io/snapshot_space_limit: "50"         // default 40%. Percentage of Vol size.
  
  spec:
    storageClassName: robin
    dataSource:
      name: mypvc-snap1
      kind: VolumeSnapshot
      apiGroup: snapshot.storage.k8s.io
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
  

  Create the clone by running the following command:

  $ kubectl create -f take-clone.yaml
  persistentvolumeclaim/mypvc-clone-snap1 created
  

• Confirm that the PersistentVolumeClaim for Clone is created:

  One can verify that the clone was successfully created by issuing the following command:

  $ kubectl get pvc
  NAME                STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
  mypvc               Bound    pvc-83ed719a-5500-11e9-a0b7-00155d320462   1Gi        RWO            robin          49m
  mypvc-clone-snap1   Bound    pvc-6dd554d1-5506-11e9-a0b7-00155d320462   1Gi        RWO            robin          7m19s
  

4.8. Expand Volumes

Robin supports volume expansion. To expand a pvc do the following.

• List the PersistentVolumes:

  In order to list all the available PV’s available on the cluster, run the following command:

  $ kubectl get pv -n robinapps
  NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM               STORAGECLASS   REASON   AGE
  pvc-651722f9-dad2-4d62-85d9-de556bb8d555   8Gi        RWO            Delete           Bound    robinapps/mysqldb   robin                   14h
  

• Edit the PersistentVolume:

  Next we need to edit the desired PersistentVolume. Under the spec section change the storage attribute under capacity field to the desired value as hightlighted below:

  $ kubectl edit persistentVolume/pvc-651722f9-dad2-4d62-85d9-de556bb8d555  -n robinapps
  

    -------
    # Please edit the object below. Lines beginning with a '#' will be ignored,
    # and an empty file will abort the edit. If an error occurs while saving this file will be
    # reopened with the relevant failures.
    #
    apiVersion: v1
    kind: PersistentVolume
    metadata:
      annotations:
        pv.kubernetes.io/provisioned-by: robin
      creationTimestamp: "2020-10-06T04:44:39Z"
      finalizers:
      - kubernetes.io/pv-protection
      - external-attacher/robin
      managedFields:
      - apiVersion: v1
        fieldsType: FieldsV1
        fieldsV1:
          f:metadata:
            f:finalizers:
              v:"external-attacher/robin": {}
        manager: csi-attacher
        operation: Update
        time: "2020-10-06T04:44:39Z"
      - apiVersion: v1
        fieldsType: FieldsV1
        fieldsV1:
          f:metadata:
            f:annotations:
              .: {}
              f:pv.kubernetes.io/provisioned-by: {}
          f:spec:
            f:accessModes: {}
            f:capacity: {}
            f:claimRef:
              .: {}
              f:apiVersion: {}
              f:kind: {}
              f:name: {}
              f:namespace: {}
              f:resourceVersion: {}
              f:uid: {}
            f:csi:
              .: {}
              f:driver: {}
              f:fsType: {}
              f:volumeAttributes:
                .: {}
                f:csi.storage.k8s.io/pv/name: {}
                f:csi.storage.k8s.io/pvc/name: {}
                f:csi.storage.k8s.io/pvc/namespace: {}
                f:storage.kubernetes.io/csiProvisionerIdentity: {}
              f:volumeHandle: {}
            f:persistentVolumeReclaimPolicy: {}
            f:storageClassName: {}
            f:volumeMode: {}
        manager: csi-provisioner
        operation: Update
        time: "2020-10-06T04:44:39Z"
      - apiVersion: v1
        fieldsType: FieldsV1
        fieldsV1:
          f:status:
            f:phase: {}
        manager: kube-controller-manager
        operation: Update
        time: "2020-10-06T04:44:39Z"
      - apiVersion: v1
        fieldsType: FieldsV1
        fieldsV1:
          f:spec:
            f:capacity:
              f:storage: {}
        manager: kubectl
        operation: Update
        time: "2020-10-06T19:25:31Z"
      name: pvc-651722f9-dad2-4d62-85d9-de556bb8d555
      resourceVersion: "4678372"
      selfLink: /api/v1/persistentvolumes/pvc-651722f9-dad2-4d62-85d9-de556bb8d555
      uid: 0151065d-fd69-4479-85e2-d4c47c414a90
    spec:
      accessModes:
      - ReadWriteOnce
      capacity:
        storage: 16Gi
      claimRef:
        apiVersion: v1
        kind: PersistentVolumeClaim
        name: mysqldb
        namespace: robinapps
        resourceVersion: "4415500"
        uid: 651722f9-dad2-4d62-85d9-de556bb8d555
      csi:
        driver: robin
        fsType: ext4
        volumeAttributes:
          csi.storage.k8s.io/pv/name: pvc-651722f9-dad2-4d62-85d9-de556bb8d555
          csi.storage.k8s.io/pvc/name: mysqldb
          csi.storage.k8s.io/pvc/namespace: robinapps
          storage.kubernetes.io/csiProvisionerIdentity: 1601911186270-8081-robin
        volumeHandle: "1601911167:5"
      persistentVolumeReclaimPolicy: Delete
      storageClassName: robin
      volumeMode: Filesystem
    status:
      phase: Bound
    -------
    persistentvolume/pvc-651722f9-dad2-4d62-85d9-de556bb8d555 edited
  

• Verify the change to the PersistentVolume:

  Lastly confirm that the PersistantVolume’s capacity has been increased by running the following command:

  $ kubectl get pv -n robinapps
  NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM               STORAGECLASS   REASON   AGE
  pvc-651722f9-dad2-4d62-85d9-de556bb8d555   16Gi       RWO            Delete           Bound    robinapps/mysqldb   robin                   14h
  

4.9. Thin Provisioning

Robin supports Thin Provisioning of the Volumes so that large storage volumes can be created without upfront physical capacity. Thin Provisioning is disabled by default and can be enabled on a cluster by changing the robin config storage_provision_factor.

• Check current Thin Provisioning factor:

  Check the current setting and also current storage capacity on the cluster. Notice the Free/Max column for the drives.

  $ robin config list server storage_provision_factor
  Section | Attribute                | Value
  --------+--------------------------+-------
  server  | storage_provision_factor | 0.8
  
  $ robin drive list
  ID | WWN                                       | Host        | Path /dev/disk/by-id                          | Size(GB) | Movable | Type | Free/Max(GB) | Vols | Role    | Status | LastOpr | Write Unit
  ---+-------------------------------------------+-------------+-----------------------------------------------+----------+---------+------+--------------+------+---------+--------+---------+------------
  1  | 0xQEMU_QEMU_HARDDISK_4a92cb43-9402-417a-9 | vnode-95-30 | scsi-0QEMU_QEMU_HARDDISK_4a92cb43-9402-417a-9 | 50       | N       | HDD  | 38/38 (100%) | 0/10 | Storage | ONLINE | READY   | 512
  3  | 0xQEMU_QEMU_HARDDISK_276268ff-b7e4-4a9c-a | vnode-95-39 | scsi-0QEMU_QEMU_HARDDISK_276268ff-b7e4-4a9c-a | 50       | N       | HDD  | 38/38 (100%) | 0/10 | Storage | ONLINE | READY   | 512
  2  | 0xQEMU_QEMU_HARDDISK_e85533b3-da77-42ba-9 | vnode-95-96 | scsi-0QEMU_QEMU_HARDDISK_e85533b3-da77-42ba-9 | 50       | N       | HDD  | 30/38 (79%)  | 1/10 | Storage | ONLINE | READY   | 512
  

• Update Thin Provisioning factor:

  Update the Thin Provisioning factor validate that visible capacity on the cluster has been updated.

  $ robin config update server storage_provision_factor 2
  The 'server' attribute 'storage_provision_factor' has been updated
  
  $ robin config list server storage_provision_factor
  Section | Attribute                | Value
  --------+--------------------------+-------
  server  | storage_provision_factor | 2
  
  $ robin drive list
  ID | WWN                                       | Host        | Path /dev/disk/by-id                          | Size(GB) | Movable | Type | Free/Max(GB) | Vols | Role    | Status | LastOpr | Write Unit
  ---+-------------------------------------------+-------------+-----------------------------------------------+----------+---------+------+--------------+------+---------+--------+---------+------------
  1  | 0xQEMU_QEMU_HARDDISK_4a92cb43-9402-417a-9 | vnode-95-30 | scsi-0QEMU_QEMU_HARDDISK_4a92cb43-9402-417a-9 | 50       | N       | HDD  | 96/96 (100%) | 0/10 | Storage | ONLINE | READY   | 512
  3  | 0xQEMU_QEMU_HARDDISK_276268ff-b7e4-4a9c-a | vnode-95-39 | scsi-0QEMU_QEMU_HARDDISK_276268ff-b7e4-4a9c-a | 50       | N       | HDD  | 96/96 (100%) | 0/10 | Storage | ONLINE | READY   | 512
  2  | 0xQEMU_QEMU_HARDDISK_e85533b3-da77-42ba-9 | vnode-95-96 | scsi-0QEMU_QEMU_HARDDISK_e85533b3-da77-42ba-9 | 50       | N       | HDD  | 88/96 (92%)  | 1/10 | Storage | ONLINE | READY   | 512
  
  Only storage disks are shown. Issue `robin disk list --role all` to view all disks
  

Note

When Thin Provisioning is enabled and application writes data it takes up physical space on the disk. There is a possibility that Application sees out of space issues when thin provsioned clusters are not actively managed. For example, a drive with size 100GB can host 2 volumes with total size of 200GB and if combined data written to those volumes goes above 100GB, the volumes would see ERR_NOSPACE errors and filesystem would be moved to Read only state.

4.10. Handling Disruptions

With Robin, highly available applications can be deployed on Kubernetes as ROBIN can handle failures of drives, rack or hosts automatically. On a Baremetal setup, volumes can be setup with a replication factor of 2 or 3 to ensure that storage is available even if a drive fails. Users can also choose the fault domain to be ‘host’ to protect against node reboots or lost.

However, in a public cloud environment the cloud disks can be detached from one cloud node and reattached to another one. For example, in AWS an EBS volume can be detached on one EC2 host and reattached to a different EC2 host. Same with GCP where a PD can be moved across GCE nodes. If a cloud node (EC2, GCE, Azure VM) is terminated or rebooted, one would want any cloud drive attached to them (EBS, PD, Block) to be moved to the one or more of the remaining healthy nodes automatically. This is not limited to just cloud disks, but also SAN LUNS that are offered to ROBIN as disks. The SAN LUNS can also be multi-mounted onto multiple nodes or moved around from node to node. User can still choose to replicate volume on public cloud as it takes sometime to detach and attach drives on cloud platforms.

Just having the storage available during a disruption will not help if Kubernetes can not access it from the Pod. For example a Kubernetes StatefulSet serializes the mounting and unmounting of a volume to protect against possible corruptions. ROBIN utilizes smart detection techniques to ensure that even if a volume is mounted on multiple nodes, it can differentiate the IOs issued from the previous stale mount and the new mount. With this consistency guarantees, ROBIN enables the Kubernetes StatefulSet to unmount a volume from a dead node and remount it on a healthy node where the Pod is scheduled to run. ROBIN actively monitors these events to allow for the fast failover of the Pods without user intervention and consequently enables users to reliably deploy highly available stateful applications on Kubernetes.