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I am trying to deploy Cassandra on my local Kind cluster running on my Ubuntu 22.04 machine. The only instruction I found is this, that uses a StatefulSet for that. I am just wondering to know, isn't a Deployment file something newer? Why they didn't use Deployment file instead of StatefulSet? If it is better to use a Deployment file, can anybody help me to convert this StatefulSet to a Deployment file?

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: cassandra
  labels:
    app: cassandra
spec:
  serviceName: cassandra
  replicas: 3
  selector:
    matchLabels:
      app: cassandra
  template:
    metadata:
      labels:
        app: cassandra
    spec:
      terminationGracePeriodSeconds: 1800
      containers:
      - name: cassandra
        image: gcr.io/google-samples/cassandra:v13
        imagePullPolicy: Always
        ports:
        - containerPort: 7000
          name: intra-node
        - containerPort: 7001
          name: tls-intra-node
        - containerPort: 7199
          name: jmx
        - containerPort: 9042
          name: cql
        resources:
          limits:
            cpu: "500m"
            memory: 1Gi
          requests:
            cpu: "500m"
            memory: 1Gi
        securityContext:
          capabilities:
            add:
              - IPC_LOCK
        lifecycle:
          preStop:
            exec:
              command: 
              - /bin/sh
              - -c
              - nodetool drain
        env:
          - name: MAX_HEAP_SIZE
            value: 512M
          - name: HEAP_NEWSIZE
            value: 100M
          - name: CASSANDRA_SEEDS
            value: "cassandra-0.cassandra.default.svc.cluster.local"
          - name: CASSANDRA_CLUSTER_NAME
            value: "K8Demo"
          - name: CASSANDRA_DC
            value: "DC1-K8Demo"
          - name: CASSANDRA_RACK
            value: "Rack1-K8Demo"
          - name: POD_IP
            valueFrom:
              fieldRef:
                fieldPath: status.podIP
        readinessProbe:
          exec:
            command:
            - /bin/bash
            - -c
            - /ready-probe.sh
          initialDelaySeconds: 15
          timeoutSeconds: 5
        # These volume mounts are persistent. They are like inline claims,
        # but not exactly because the names need to match exactly one of
        # the stateful pod volumes.
        volumeMounts:
        - name: cassandra-data
          mountPath: /cassandra_data

These are converted to volume claims by the controller


and mounted at the paths mentioned above.


do not use these in production until ssd GCEPersistentDisk or other


ssd pd


volumeClaimTemplates:


    

  • metadata:
  name: cassandra-data
spec:
  accessModes: [ "ReadWriteOnce" ]
  storageClassName: fast
  resources:
    requests:
      storage: 1Gi
    • 





kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: fast
provisioner: k8s.io/minikube-hostpath
parameters:
  type: pd-ssd
larsks
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best_of_man
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1 Answers1

1

A StatefulSet is different from a Deployment. From the documentation:

Like a Deployment, a StatefulSet manages Pods that are based on an identical container spec. Unlike a Deployment, a StatefulSet maintains a sticky identity for each of their Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.

You use StatefulSets when your pods need to maintain some sort of unique state -- for example, the volumeClaimTemplates section of the manifest means that each pod gets a unique PersistentVolumeClaim. This isn't possible using a Deployment.

In general you cannot convert a StatefulSet into a Deployment unless you only plan on having a single replica.

larsks
  • 47,453