Inject Containers and Volumes

How to inject custom init-containers, containers and volumes into the Cassandra pods.

Since v1.2, K8ssandra-operator allows injecting custom init containers, containers and volumes into the Cassandra pods.

Injecting (init-)containers

Custom init-containers and containers can be injected into the Cassandra pods through the .spec.cassandra.initContainers and .spec.cassandra.containers fields. These can be overriden at the datacenter level by setting the .spec.cassandra.datacenters[].initContainers and .spec.cassandra.dataceners[].containers fields.

apiVersion: k8ssandra.io/v1alpha1
kind: K8ssandraCluster
metadata:
  name: test
spec:
  cassandra:
    serverVersion: 4.0.3
    datacenters:
      - metadata:
          name: dc1
        size: 1
        storageConfig:
          cassandraDataVolumeClaimSpec:
            storageClassName: standard
            accessModes:
              - ReadWriteOnce
            resources:
              requests:
                storage: 5Gi
        initContainers:
          - name: init-busybox
            image: busybox
            command: ["sleep", "10"]
        containers:
          - name: busybox
            image: busybox
            command: ["sleep", "3600"]

The above example will inject the init-busybox init-container and the busybox container into the Cassandra pods, respectively in first position within their kinds. Fine grained control over the order of the injected init-containers can be achieved by also specifying the init-containers that K8ssandra-operator or cass-operator will add during the reconcile, and that should appear before the custom containers:

apiVersion: k8ssandra.io/v1alpha1
kind: K8ssandraCluster
metadata:
  name: test
spec:
  cassandra:
    serverVersion: 4.0.3
    datacenters:
      - metadata:
          name: dc1
        size: 1
        storageConfig:
          cassandraDataVolumeClaimSpec:
            storageClassName: standard
            accessModes:
              - ReadWriteOnce
            resources:
              requests:
                storage: 5Gi
        initContainers:
          - name: server-config-init
          - name: init-busybox
            image: busybox
            command: ["sleep", "10"]
        containers:
          - name: busybox
            image: busybox
            command: ["sleep", "3600"]

In the above example, the init-busybox container will be injected right after the server-config-init init-container. The order of the main containers doesn’t have any impact as they all start concurrently.

K8ssandra-operator is likely to generate the following init-containers in this order:

  • jmx-credentials: always generated (Removed in v1.5.0)
  • medusa-restore: generated if Medusa is enabled

cass-operator will generate the following init-container:

  • server-config-init: always generated

Note: The medusa-restore init-container must always be placed after the server-config-init one.

K8ssandra-operator is likely to generate the following container:

  • medusa: generated if Medusa is enabled

cass-operator will generate the following containers in this order:

  • cassandra: always generated
  • server-system-logger: always generated

Injecting volumes

Extra volumes can be injected into the Cassandra pods through the .spec.cassandra.extraVolumes field. This field allows to specify two types of volumes:

  • standard volume definitions that will be added to the Cassandra pods (.spec.cassandra.extraVolumes.volumes), and required to be mounted explicitly in the containers.
  • PVC volumes which will be mounted automatically by cass-operator and managed by the Cassandra statefulset (.spec.cassandra.extraVolumes.pvcs).
apiVersion: k8ssandra.io/v1alpha1
kind: K8ssandraCluster
metadata:
  name: test
spec:
  cassandra:
    serverVersion: 4.0.3
    datacenters:
      - metadata:
          name: dc1
        k8sContext: kind-k8ssandra-0
        size: 1
        storageConfig:
          cassandraDataVolumeClaimSpec:
            storageClassName: standard
            accessModes:
              - ReadWriteOnce
            resources:
              requests:
                storage: 5Gi
        initContainers:
          - name: "server-config-init"
          - name: init-busybox
            image: busybox
            command: ["sleep", "10"]
            volumeMounts:
              - name: busybox-vol
                mountPath: /etc/busybox
        containers:
          - name: "cassandra"
          - name: "server-system-logger"
          - name: busybox
            image: busybox
            command: ["sleep", "3600"]
            volumeMounts:
              - name: busybox-vol
                mountPath: /etc/busybox
        extraVolumes:
          volumes:
            - name: busybox-vol
              emptyDir: {}
          pvcs:
            - name: sts-extra-vol
              mountPath: "/etc/extra"
              pvcSpec:
                storageClassName: standard
                accessModes:
                  - ReadWriteOnce
                resources:
                  requests:
                    storage: 10Mi

The above example adds an emptyDir volume named busybox-vol, which is mounted in the init-busybox init-container and the busybox container. It also adds a PVC volume named sts-extra-vol, which is managed by the Cassandra statefulset and mounted on all containers created by cass-operator under /etc/extra. That includes server-system-logger and cassandra. Mounting this volume into other (init-)containers should be done explicitly.

Next steps

  • Explore other K8ssandra Operator tasks.
  • See the Reference topics for information about K8ssandra Operator Custom Resource Definitions (CRDs) and the single K8ssandra Operator Helm chart.

Last modified June 12, 2024: Release v1.17.0 (8804770)