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OpenEBS for PostgreSQL

OpenEBS and PostgreSQL


Introduction


OpenEBS is deployed under PostgreSQL for a variety of reasons discussed below. The basics are that PostgreSQL is typically deployed as a StatefulSet on Kubernetes and requires persistent storage for each instance of PostgreSQL StorageManager. OpenEBS provides persistent volumes on the fly when StorageManagers are scaled up.


Advantages of using OpenEBS for PostgreSQL database:

  • No need to manage the local disks, they are managed by OpenEBS
  • Large size PVs can be provisioned by OpenEBS and PostgreSQL
  • Start with small storage and add disks as needed on the fly. Sometimes PostgreSQL instances are scaled up because of capacity on the nodes. With OpenEBS persistent volumes, capacity can be thin provisioned and disks can be added to OpenEBS on the fly without disruption of service
  • PostgreSQL sometimes need highly available storage, in such cases OpenEBS volumes can be configured with 3 replicas.
  • If required, OpenEBS can be used to take backups of the PostgreSQL data periodically and back them up to S3 or to any object storage or to other PVs backed by OpenEBS so that restoration of the same data is possible to the same or any other Kubernetes cluster


Note: PostgreSQL can be deployed both as deployment or as statefulset. When PostgreSQL deployed as statefulset, you would not typically also replicate the data at OpenEBS level. When PostgreSQL is deployed as a deployment, consider 3 OpenEBS replicas, and choose your the StorageClass accordingly.



Deployment model


OpenEBS and PostgreSQL

As shown above, OpenEBS volumes need to be configured with single replica. This configuration works fine when the nodes (hence the OpenEBS cStor pool) is deployed across Kubernetes zones.



Configuration workflow


  1. Install OpenEBS

    If OpenEBS is not installed in your K8s cluster, this can done from here. If OpenEBS is already installed, go to the next step.

  2. Configure cStor Pool

    If cStor Pool is not configured in your OpenEBS cluster, this can be done from here. As PostgreSQL is a StatefulSet application, it requires single storage replication factor. During cStor Pool creation, make sure that the maxPools parameter is set to >=3. If cStor pool is already configured, go to the next step. Sample YAML named openebs-config.yaml for configuring cStor Pool is provided in the Configuration details below.

  3. Create Storage Class

    You must configure a StorageClass to provision cStor volume on cStor pool. In this solution we are using a StorageClass to consume the cStor Pool which is created using external disks attached on the Nodes. The storage pool is created using the steps provided in the Step 3. In this solution,PostgreSQL is a deployment. Since it requires replication at the storage level so cStor volume replicaCount is 3. Sample YAML named openebs-sc-disk.yaml to consume cStor pool with cStor volume replica count as 3 is provided in the configuration details below.

  4. Launch and test PostgreSQL

    Install PostgreSQL deployment on OpenEBS volume using the following command.

    helm install --name my-release --set persistence.storageClass=openebs-cstor-disk  stable/postgresql

    This will create a PostgreSQL deployment with 3 replica of cStor volume with a PVC size of 8Gi. More details can be read from here.



Reference at openebs.ci


A live deployment of PostgreSQL using OpenEBS volumes can be seen at the website www.openebs.ci

Deployment YAML spec files for PostgreSQL and OpenEBS resources are found here

OpenEBS-CI dashboard of PostgreSQL



Post deployment Operations


Monitor OpenEBS Volume size

It is not seamless to increase the cStor volume size (refer to the roadmap item). Hence, it is recommended that sufficient size is allocated during the initial configuration.

Monitor cStor Pool size

In some cases the cStor pool may not be dedicated to only the PostgreSQL database. It is recommended to watch the pool capacity and add more disks to the pool before it hits 80% threshold. See cStorPool metrics.



Configuration Details


openebs-config.yaml

#Use the following YAMLs to create a cStor Storage Pool.
# and associated storage class.
apiVersion: openebs.io/v1alpha1
kind: StoragePoolClaim
metadata:
  name: cstor-disk
spec:
  name: cstor-disk
  type: disk
  poolSpec:
    poolType: striped
  # NOTE - Appropriate disks need to be fetched using `kubectl get blockdevices -n openebs`
  # `Block devices` is a custom resource supported by OpenEBS with `node-disk-manager`
  # as the disk operator
# Replace the following with actual disk CRs from your cluster `kubectl get blockdevices -n openebs`
# Uncomment the below lines after updating the actual disk names.
  blockDevices:
    blockDeviceList:
# Replace the following with actual disk CRs from your cluster from `kubectl get blockdevices -n openebs`
#   - blockdevice-69cdfd958dcce3025ed1ff02b936d9b4
#   - blockdevice-891ad1b581591ae6b54a36b5526550a2
#   - blockdevice-ceaab442d802ca6aae20c36d20859a0b
---

openebs-sc-disk.yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: openebs-cstor-disk
  annotations:
    openebs.io/cas-type: cstor
    cas.openebs.io/config: |
      - name: StoragePoolClaim
        value: "cstor-disk"
      - name: ReplicaCount
        value: "3"       
provisioner: openebs.io/provisioner-iscsi
reclaimPolicy: Delete
---



See Also:


OpenEBS architecture

OpenEBS use cases

cStor pools overview



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