********************************** Using ROBIN Storage 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. Kubernetes CSI broke compatibility between CSI v1.0 and CSI v0.3 and hence one must implement two different StorageClasses, one each for implementing v0.3 and v1.0 version of the Spec. To facilitate this ROBIN, ships with two StorageClasses: 1. ``robin-0-3``: The StorageClass that is compatible with Kubernetes versions less than v1.13 2. ``robin``: The StorageClass that is comptabile with Kubernetes versions v1.13 and above Both storage classes follow the same parameters as described below: Definition of ROBIN CSI Storage Class: .. code-block:: yaml apiVersion: storage.k8s.io/v1 kind: StorageClass metadata: name: robin provisioner: robin reclaimPolicy: Delete parameters: # media: SSD|HDD // default is media of first available drive in the cluster # blocksize: "512"|"4096" // default is 4096 # fstype: ext4|xfs // default is ext4 # replication: "2"|"3" // default is no replication # faultdomain: disk|host // default is disk # compression: LZ4 // default is no inline compression # encryption: CHACHA20|AES256|AES128 // default is no encryption # snapshot_space_limit: "50" // default 40% of Volume size. ========================= ================================================== ``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. This value is made | available via ``cat /sys/block//queue/physical_block_size`` ``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 ``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. ``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. ========================= ================================================== .. 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) ============================================= Using ROBIN StorageClass to Provision Storage ============================================= Basic Use Case -------------- **STEP 1: Create a PersistentVolumeClaim (PVC) using ROBIN StorageClass:** .. code-block:: console :emphasize-lines: 7 $ cat mypvc.yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: mypvc annotations: volume.beta.kubernetes.io/storage-class: robin spec: accessModes: - ReadWriteOnce resources: requests: storage: 10Gi $ kubectl create -f mypvc.yaml persistentvolumeclaim/mypvc created .. note:: Notice that under metadata/annotations we have spcified the storage class as ``volume.beta.kubernetes.io/storage-class: robin``. This results in the ROBIN StorageClass to be be picked up. For Kubernetes versions less than v1.13 one should instead use ``volume.beta.kubernetes.io/storage-class: robin-0-3``. **STEP 2: Confirm that the PersistentVolumeClaim and the corresponding PersistentVolume are created:** .. code-block:: console $ kubectl get pvc NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE mypvc Bound pvc-1b37154c-4764-11e9-bac1-00155d61160d 10Gi RWO robin 2s $ kubectl get pv NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE pvc-b91ee150-4790-11e9-bac1-00155d61160d 10Gi RWO Delete Bound default/mypvc robin 24s **STEP 3: Attach this PersistentVolumeClaim to a simple Pod:** .. code-block:: console $ cat mypod.yaml 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 $ kubectl create -f mypod.yaml 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 blow below. Please notice that each annotations are prefixed with ``robin.io/``. Annotations can take exact same parameters as in ROBIN StorageClass and would override the corrosponding parameters specified in the StorageClass. .. code-block:: console :emphasize-lines: 6-11 $ cat newpvc.yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: proteced-compressed-pvc annotations: volume.beta.kubernetes.io/storage-class: robin robin.io/replication: "3" robin.io/faultdomain: host robin.io/compression: LZ4 robin.io/media: SSD spec: accessModes: - ReadWriteOnce resources: requests: storage: 1Gi $ kubectl create -f newpvc.yaml persistentvolumeclaim/proteced-compressed-pvc created .. note:: Note that the number 3 is quoted as ``"3"`` when specifying ``robin.io/replication:`` annotation. This is per the Kubernetes Spec. Not doing so would result in an error being thrown by kubectl Using ROBIN Storage 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 as follows: .. code-block:: console :emphasize-lines: 44-47 $ cat myweb.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: volume.beta.kubernetes.io/storage-class: robin robin.io/replication: "2" robin.io/media: HDD spec: accessModes: [ "ReadWriteOnce" ] resources: requests: storage: 1Gi $ 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 .. _StorageForHelmCharts: 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 Storage for persistent storage one needs to pass it as ``--set persistence.storageClass==robin`` command line option as shown below: .. code-block:: console $ helm install stable/mysql --set persistence.storageClass=robin This would result in ROBIN being used as the storage provisioner for PersistentVolumeClaims created by this helm chart. ===================================================== 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: ""`` and optionally ``robin.io/faultdomain: disk|host`` as shown below: .. code-block:: console :emphasize-lines: 8-9 $ cat replicated-pvc.yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: replicated-pvc annotations: volume.beta.kubernetes.io/storage-class: robin robin.io/replication: "3" robin.io/faultdomain: host spec: accessModes: - ReadWriteOnce resources: requests: storage: 1Gi Setting the correct value for ``robin.io/fautdomain`` to either ``disk`` or ``host`` 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. ===================================== 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 Storage as the default Kubernetes StorageClass. This can be done as follows: **STEP 1: Inspect if there is already a different StorageClass marked as default**:: $ kubectl get storageclass NAME PROVISIONER AGE standard (default) kubernetes.io/gce-pd 11d robin robin 1d **STEP 2: Mark the current, non ROBIN StorageClass as "non-default" before proceeding to the next step**:: $ kubectl patch storageclass standard \ -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. **STEP 3: Now mark ROBIN as the new default StorageClass**:: $ 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` **STEP 4: Confirm that ROBIN is now the default StorageClass:** .. code-block:: console :emphasize-lines: 4 $ kubectl get storageclass NAME PROVISIONER AGE standard kubernetes.io/gce-pd 11d robin (default) robin 1d To learn more see official documentation on how to `Change the default StorageClass `_. ================ 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 v1.13 and beyond. **STEP 1: Register a SnapshotClass with Kubernetes**: .. code-block:: console $ cat robin-snapshot-class.yaml apiVersion: snapshot.storage.k8s.io/v1alpha1 kind: VolumeSnapshotClass metadata: name: robin-snapshotclass snapshotter: robin $ kubectl create -f robin-snapshot-class.yaml volumesnapshotclass.snapshot.storage.k8s.io/robin-snapshotclass created **STEP 2: Confirm that a SnapshotClass is registered**: .. code-block:: console $ kubectl get volumesnapshotclass NAME AGE robin-snapshotclass 12h **STEP 3: Take a snapshot of a PersistentVolumeClaim**: .. code-block:: console $ cat take-snapshot.yaml apiVersion: snapshot.storage.k8s.io/v1alpha1 kind: VolumeSnapshot metadata: name: mypvc-snapshot spec: snapshotClassName: robin-snapshotclass source: name: mypvc kind: PersistentVolumeClaim $ kubectl create -f take-snapshot.yaml volumesnapshot.snapshot.storage.k8s.io/mypvc-snapshot created **STEP 4: Confirm that the VolumeSnapshot for the PersistentVolumeClaim is created**: .. code-block:: console $ kubectl get volumesnapshot NAME AGE mypvc-snapshot 1s $ kubectl get volumesnapshotcontent NAME AGE snapcontent-415d53bc-481a-11e9-bac1-00155d61160d 1s ================ Clone Volumes ================ ROBIN has a capability of taking a clone from a snapshot of a volume. We allow user 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:: Clone is still an Alpha feature in Kubernetes so it requires ``VolumeSnapshotDataSource`` feature gate be `enabled `_ on the apiserver and controller-manager. **STEP 1: Take a Clone of a VolumeSnapshot**: .. code-block:: console $ cat take-clone.yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: mypvc-clone-snap1 #annotations: # robin.io/media: # robin.io/replication: <"2", "3"> # robin.io/faultdomain: // default disk # robin.io/encryption: # 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 $ kubectl create -f take-clone.yaml persistentvolumeclaim/mypvc-clone-snap1 created **STEP 4: Confirm that the PersistentVolumeClaim for Clone is created**: .. code-block:: console $ 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 ================================================ 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.