Terminate Kubernetes Nodes

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Modify the DSECluster manifest (object) specification and submit that change with the kubectl command to terminate one or more nodes within a datacenter in a Kubernetes Cluster.

Prerequisites

kubectl
Kubeconfig file or context pointing to a Control Plane Kubernetes cluster
A Kubernetes Data Plane cluster
An existing DSECluster manifest specifying one datacenter with three DSE nodes distributed equally across three racks.

Procedure

Review a DSECluster manifest named demo-dse.yaml that was used to create the datacenter. In that manifest the datacenters: size field is set at 6, specifying six DSE nodes equally distributed across three racks.

...
datacenters:
    - metadata:
        name: dc1
      k8sContext: east
      size: 6
      racks:
        - name: rack1
          nodeAffinityLabels:
            topology.kubernetes.io/zone: us-east1-c
        - name: rack2
          nodeAffinityLabels:
            topology.kubernetes.io/zone: us-east1-b
        - name: rack3
          nodeAffinityLabels:
            topology.kubernetes.io/zone: us-east1-d
...

Modify this DSECluster manifest to terminate one (1) node. Edit the datacenters:size: field, changing 6 to 5:

...
datacenters:
    - metadata:
        name: dc1
      k8sContext: east
      size: 5
      racks:
...

Submit this change in the Control Plane cluster to initiate the terminatation operation:
```
kubectl apply -f demo-dse.yaml
```
The node is terminated from the last rack that was specified. The StatefulSet per rack is also a factor and must be 1 before a node is terminated. For example, the operation’s algorithm chooses to terminate demo-dc1-rack3-sts-1 given the following nodes:
```
demo-dc1-rack3-sts-0

demo-dc1-rack3-sts-1
```
At any given time the number of started DSE nodes in a rack cannot be more or less than the number of started nodes in all other racks by more than one.

Monitor the status of the CassandraDatacenter with this command:

kubectl get cassandradatacenter dc1 -o yaml

Click to reveal the sample output:

status:
  cassandraOperatorProgress: Updating
  conditions:
  - lastTransitionTime: "2022-10-20T02:43:33Z"
    message: ""
    reason: ""
    status: "True"
    type: Healthy
  - lastTransitionTime: "2022-10-20T02:49:05Z"
    message: ""
    reason: ""
    status: "False"
    type: Stopped
  - lastTransitionTime: "2022-10-20T02:49:05Z"
    message: ""
    reason: ""
    status: "False"
    type: ReplacingNodes
  - lastTransitionTime: "2022-10-20T03:19:22Z"
    message: ""
    reason: ""
    status: "False"
    type: Updating
  - lastTransitionTime: "2022-10-20T02:49:05Z"
    message: ""
    reason: ""
    status: "False"
    type: RollingRestart
  - lastTransitionTime: "2022-10-20T02:49:05Z"
    message: ""
    reason: ""
    status: "False"
    type: Resuming
  - lastTransitionTime: "2022-10-20T14:57:59Z"
    message: ""
    reason: ""
    status: "True"
    type: ScalingDown
  - lastTransitionTime: "2022-10-20T02:49:05Z"
    message: ""
    reason: ""
    status: "True"
    type: Valid
  - lastTransitionTime: "2022-10-20T02:49:05Z"
    message: ""
    reason: ""
    status: "True"
    type: Initialized
  - lastTransitionTime: "2022-10-20T02:49:05Z"
    message: ""
    reason: ""
    status: "True"
    type: Ready
  - lastTransitionTime: "2022-10-20T03:19:22Z"
    message: ""
    reason: ""
    status: "False"
    type: ScalingUp
  lastServerNodeStarted: "2022-10-20T03:16:15Z"
  nodeStatuses:
    demo-dc1-rack1-sts-0:
      hostID: fedbd183-6075-4251-a37d-76102845919a
    demo-dc1-rack1-sts-1:
      hostID: b77157d1-829b-4965-9f64-4590104e7b9f
    demo-dc1-rack2-sts-0:
      hostID: 5ed4767f-b827-469e-b78e-2ceaab71943e
    demo-dc1-rack2-sts-1:
      hostID: 73813553-e081-42da-8f45-6fb67faf309b
    demo-dc1-rack3-sts-0:
      hostID: 3b456f44-556d-4f6f-9f25-5aae048f8aa8
    demo-dc1-rack3-sts-1:
      hostID: 5f316bf0-3e39-40c0-8a66-4998337336bf
  observedGeneration: 3
  quietPeriod: "2022-10-20T14:36:38Z"
  superUserUpserted: "2022-10-20T14:36:33Z"
  usersUpserted: "2022-10-20T14:36:33Z"

The ScalingDown condition has status: "True" indicating that the scaling down operation is in progress. Cass Operator updates it to "False" when the operation is complete.

Monitor the DSE node logs to verify that the node is terminated with this command:

kubectl logs -f demo-dc1-rack3-sts-1 -c server-system-logger

Sample output:

...
INFO  [pool-20-thread-1] 2022-10-20 14:58:30,229  StreamResultFuture.java:108 - [Stream plan: a8c715e0-5087-11ed-910e-b52a292b413b session: 0/10.100.5.12] Initiated streaming session for Unbootstrap
INFO  [pool-20-thread-1] 2022-10-20 14:58:30,230  StorageService.java:2143 - LEAVING: streaming hints to other nodes
INFO  [Stream-Connection-Establisher:2] 2022-10-20 14:58:30,233  StreamSession.java:385 - [Stream plan: a8c715e0-5087-11ed-910e-b52a292b413b session: 0/10.100.5.12] Starting streaming with /10.100.5.12
INFO  [pool-20-thread-1] 2022-10-20 14:58:30,234  HintsService.java:230 - Resumed hints dispatch
INFO  [HintsDispatcher:3] 2022-10-20 14:58:30,238  HintsDispatchExecutor.java:163 - Transferring all hints to /10.100.5.12: 3b456f44-556d-4f6f-9f25-5aae048f8aa8
INFO  [Stream-Connection-Establisher:2] 2022-10-20 14:58:30,241  StreamCoordinator.java:291 - [Stream plan: a8c715e0-5087-11ed-910e-b52a292b413b session: 0/10.100.5.12] Beginning stream session with /10.100.5.12
INFO  [Stream-Deserializer-10.100.5.12/10.100.5.12:7000-6c5d4795] 2022-10-20 14:58:30,249  StreamResultFuture.java:198 - [Stream plan: a8c715e0-5087-11ed-910e-b52a292b413b session: 0/10.100.5.12] Prepare completed. Receiving 0 files(0.000KiB), sending 2 files(121.051KiB)
INFO  [Stream-Serializer-/10.100.5.12:1] 2022-10-20 14:58:30,291  StreamLimiter.java:64 - Configured stream limiter with local DC throughput at 25MB/s and buffer size of 25MB, inter DC throughput at 25MB/s and buffer size of 25MB
INFO  [Stream-Deserializer-10.100.5.12/10.100.5.12:7000-6c5d4795] 2022-10-20 14:58:31,605  StreamResultFuture.java:212 - [Stream plan: a8c715e0-5087-11ed-910e-b52a292b413b session: 0/10.100.5.12] Session with /10.100.5.12 is complete
INFO  [Stream-Deserializer-10.100.5.12/10.100.5.12:7000-6c5d4795] 2022-10-20 14:58:31,615  StreamResultFuture.java:249 - [Stream plan: a8c715e0-5087-11ed-910e-b52a292b413b] All sessions completed org.apache.cassandra.streaming.StreamState@51ae56f3
INFO  [pool-20-thread-1] 2022-10-20 14:58:31,622  StorageService.java:3474 - Removing tokens [7174889864644096175, -5340669455939452840, 6589226831831228631, -3361306996063616279, -2877281716039476745, -6917033737490471623, -4440678482902958568, -5921294927776755314, 6562241473441405040, -8205472916598434127, -1406860119728070875, 4559174963203125054, -3911541421963556594, 7899698028842487330, -3141618503503578628, -2561210462966576697] for /10.100.3.7
INFO  [pool-20-thread-1] 2022-10-20 14:58:31,631  Gossiper.java:1301 - InetAddress /10.100.3.7 is now DOWN
INFO  [pool-20-thread-1] 2022-10-20 14:58:31,638  StorageService.java:4968 - Announcing that I have left the ring for 30000ms

The node (pod) is terminated after the termination operation completes. Cass Operator removes the demo-dc1-rack3-sts-1 node from the nodeStatuses map.