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Storage Guide

How to configure storage options for the Altinity Kubernetes Operator

The Altinity Kubernetes Operator users have different options regarding persistent storage depending on their environment and situation. The following guides detail how to set up persistent storage for local and cloud storage environments.

1 - Persistent Storage Overview

Allocate persistent storage for Altinity Kubernetes Operator clusters

Users setting up storage in their local environments can establish persistent volumes in different formats based on their requirements.

Allocating Space

Space is allocated through the Kubernetes PersistentVolume object. ClickHouse clusters established with the Altinity Kubernetes Operator then use the PersistentVolumeClaim to receive persistent storage.

The PersistentVolume can be set in one of two ways:

  • Manually: Manual allocations set the storage area before the ClickHouse cluster is created. Space is then requested through a PersistentVolumeClaim when the ClickHouse cluster is created.
  • Dynamically: Space is allocated when the ClickHouse cluster is created through the PersistentVolumeClaim, and the Kubernetes controlling software manages the process for the user.

For more information on how persistent volumes are managed in Kubernetes, see the Kubernetes documentation Persistent Volumes.

Storage Types

Data stored for ClickHouse clusters in the following ways:

No Persistent Storage

If no persistent storage claim template is specified, then no persistent storage will be allocated. When Kubernetes is stopped or a new manifest applied, all previous data will be lost.

In this example two shards are specified but has no persistent storage allocated:

apiVersion: "clickhouse.altinity.com/v1"
kind: "ClickHouseInstallation"
metadata:
  name: "no-persistent"
spec:
  configuration:
    clusters:
      - name: "no-persistent"
        layout:
          shardsCount: 2
          replicasCount: 1

When applied to the namespace test, no persistent storage is found:

kubectl -n test get pv
No resources found

Cluster Wide Storage

If neither the dataVolumeClaimTemplate or the logVolumeClaimTemplate are specified (see below), then all data is stored under the requested volumeClaimTemplate. This includes all information stored in each pod.

In this example, two shards are specified with one volume of storage that is used by the entire pods:

apiVersion: "clickhouse.altinity.com/v1"
kind: "ClickHouseInstallation"
metadata:
  name: "cluster-storage"
spec:
  configuration:
    clusters:
      - name: "cluster-storage"
        layout:
          shardsCount: 2
          replicasCount: 1
        templates:
            volumeClaimTemplate: cluster-storage-vc-template
  templates:
    volumeClaimTemplates:
      - name: cluster-storage-vc-template
        spec:
          storageClassName: standard
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 500Mi

When applied to the namespace test the following persistent volumes are found. Note that each pod has 500Mb of storage:

kubectl -n test get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                                                        STORAGECLASS   REASON   AGE
pvc-6e70c36a-f170-47b5-93a6-88175c62b8fe   500Mi      RWO            Delete           Bound    test/cluster-storage-vc-template-chi-cluster-storage-cluster-storage-1-0-0   standard                21s
pvc-ca002bc4-0ad2-4358-9546-0298eb8b2152   500Mi      RWO            Delete           Bound    test/cluster-storage-vc-template-chi-cluster-storage-cluster-storage-0-0-0   standard                39s

Cluster Wide Split Storage

Applying the dataVolumeClaimTemplate and logVolumeClaimTemplate template types to the Altinity Kubernetes Operator controlled ClickHouse cluster allows for specific data from each ClickHouse pod to be stored in a particular persistent volume:

  • dataVolumeClaimTemplate: Sets the storage volume for the ClickHouse node data. In a traditional ClickHouse server environment, this would be allocated to /var/lib/clickhouse.
  • logVolumeClaimTemplate: Sets the storage volume for ClickHouse node log files. In a traditional ClickHouse server environment, this would be allocated to /var/log/clickhouse-server.

This allows different storage capacities for log data versus ClickHouse database data, as well as only capturing specific data rather than the entire pod.

In this example, two shards have different storage capacity for dataVolumeClaimTemplate and logVolumeClaimTemplate:

apiVersion: "clickhouse.altinity.com/v1"
kind: "ClickHouseInstallation"
metadata:
  name: "cluster-split-storage"
spec:
  configuration:
    clusters:
      - name: "cluster-split"
        layout:
          shardsCount: 2
          replicasCount: 1
        templates:
          dataVolumeClaimTemplate: data-volume-template
          logVolumeClaimTemplate: log-volume-template
  templates:
    volumeClaimTemplates:
      - name: data-volume-template
        spec:
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 500Mi
      - name: log-volume-template
        spec:
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 100Mi

In this case, retrieving the PersistentVolume allocations shows two storage volumes per pod based on the specifications in the manifest:

kubectl -n test get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                                                     STORAGECLASS   REASON   AGE
pvc-0b02c5ba-7ca1-4578-b3d9-ff8bb67ad412   100Mi      RWO            Delete           Bound    test/log-volume-template-chi-cluster-split-storage-cluster-split-1-0-0    standard                21s
pvc-4095b3c0-f550-4213-aa53-a08bade7c62c   100Mi      RWO            Delete           Bound    test/log-volume-template-chi-cluster-split-storage-cluster-split-0-0-0    standard                40s
pvc-71384670-c9db-4249-ae7e-4c5f1c33e0fc   500Mi      RWO            Delete           Bound    test/data-volume-template-chi-cluster-split-storage-cluster-split-1-0-0   standard                21s
pvc-9e3fb3fa-faf3-4a0e-9465-8da556cb9eec   500Mi      RWO            Delete           Bound    test/data-volume-template-chi-cluster-split-storage-cluster-split-0-0-0   standard                40s

Pod Mount Based Storage

PersistentVolume objects can be mounted directly into the pod’s mountPath. Any other data is not stored when the container is stopped unless it is covered by another PersistentVolumeClaim.

In the following example, each of the 2 shards in the ClickHouse cluster has the volumes tied to specific mount points:

apiVersion: "clickhouse.altinity.com/v1"
kind: "ClickHouseInstallation"
metadata:
  name: "pod-split-storage"
spec:
  configuration:
    clusters:
      - name: "pod-split"
        # Templates are specified for this cluster explicitly
        templates:
          podTemplate: pod-template-with-volumes
        layout:
          shardsCount: 2
          replicasCount: 1

  templates:
    podTemplates:
      - name: pod-template-with-volumes
        spec:
          containers:
            - name: clickhouse
              image: yandex/clickhouse-server:21.8
              volumeMounts:
                - name: data-storage-vc-template
                  mountPath: /var/lib/clickhouse
                - name: log-storage-vc-template
                  mountPath: /var/log/clickhouse-server

    volumeClaimTemplates:
      - name: data-storage-vc-template
        spec:
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 500Mi
      - name: log-storage-vc-template
        spec:
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 100Mi
kubectl -n test get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                                                 STORAGECLASS   REASON   AGE
pvc-37be9f84-7ba5-404e-8299-e95a291014a8   500Mi      RWO            Delete           Bound    test/data-storage-vc-template-chi-pod-split-storage-pod-split-1-0-0   standard                24s
pvc-5b2f8694-326d-41cb-94ec-559725947b45   100Mi      RWO            Delete           Bound    test/log-storage-vc-template-chi-pod-split-storage-pod-split-1-0-0    standard                24s
pvc-84768e78-e44e-4295-8355-208b07330707   500Mi      RWO            Delete           Bound    test/data-storage-vc-template-chi-pod-split-storage-pod-split-0-0-0   standard                43s
pvc-9e123af7-01ce-4ab8-9450-d8ca32b1e3a6   100Mi      RWO            Delete           Bound    test/log-storage-vc-template-chi-pod-split-storage-pod-split-0-0-0    standard                43s