k8s-cassandra-nodeLabel2pod

cassandra-node2pod.yml

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: cassandra-rackdc
data:
  cassandra-rackdc.properties: |
    dc= datacenter
    rack= RACK
---
apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: node2pod
spec:
  replicas: 1
  template:
    metadata:
      labels:
        name: node2pod
        app: node2pod
    spec:
      initContainers:
      - name: node2pod
        imagePullPolicy: IfNotPresent
        image: <image-with-k8s-access>
        command:
        - "sh"
        - "-c"
        - "cp /config/cassandra-rackdc.properties /shared/cassandra-rackdc.properties && \
           sed -i.bak s/RACK/$(kubectl get no -Llabel | grep ${NODE_NAME} | awk '{print $6}')/g /shared/cassandra-rackdc.properties"
        env:
        - name: NODE_NAME
          valueFrom:
            fieldRef:
              fieldPath: spec.nodeName
        volumeMounts:
        - name: cassandra-rackdc
          mountPath: /config/
        - name: shared
          mountPath: /shared/
      containers:
      - name: cassandra
        image: cassandra
        volumeMounts:
        - name: shared
          mountPath: /etc/cassandra-rackdc.properties
          subPath: cassandra-rackdc.properties
      volumes:
        - name: cassandra-rackdc
          configMap:
            name: cassandra-rackdc
        - name: shared
          emptyDir: {}

Hey @gmaslowski thanks for sharing that! Wondering, don't you need to setup keys etc for accessing the kube api and execute a kubectl command through the initContainer? As it's not part of the downward API, but you execute a full kubectl command, hence it goes through the Kubernetes API

Hi @koslib. Yes, k8s access is important to be setup in "a way". Any that is convenient and secure of course. Hence the image: <image-with-k8s-access> is just there. So you either create an image with keys (not recommended) or you can inject the keys from within securely provided secrets.

Yeah maybe a ClusterRole, ClusterRoleBinding and ServiceAccount combo.

Pasting for posterity what worked for me while hacking something quick:

apiVersion: v1
kind: ServiceAccount
metadata:
  name: node-listing-sa
  namespace: default

---

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  namespace: default
  name: node-listing-clusterrole
rules:
  - apiGroups: [""]
    resources: ["nodes"]
    verbs: ["get", "list"]


---

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: node-listing-rolebinding
  namespace: default
subjects:
  - kind: ServiceAccount
    name: node-listing-sa
    namespace: default
roleRef:
  kind: ClusterRole
  name: node-listing-clusterrole
  apiGroup: rbac.authorization.k8s.io

Thanks again for the article and the gist!