Restart the DSE cluster

DataStax Mission Control is current in Private Preview. It is subject to the beta agreement executed between you and DataStax. DataStax Mission Control is not intended for production use, has not been certified for production workloads, and might contain bugs and other functional issues. There is no guarantee that DataStax Mission Control will ever become generally available. DataStax Mission Control is provided on an “AS IS” basis, without warranty or indemnity of any kind.

If you are interested in trying out DataStax Mission Control please contact your DataStax account team.

Restart all nodes in a cluster in a rolling fashion to provide zero downtime to applications. Restart nodes in a DataStax Enterprise (DSE) cluster after adding or terminating one or more nodes.

Performance Impact

Running a restart task has no significant implications on the performance or stability of the cluster as long as the replication factor (RF) is set to 3 or higher. This RF setting tolerates one node being down while maintaining quorum read and write operations.

Prerequisites

The kubectl CLI tool.
Kubeconfig file` or context pointing to a Control Plane Kubernetes cluster.

Workflow of user and operators

User defines a restart CassandraTask.
User submits a restart CassandraTask to the Data Plane Kubernetes cluster where the datacenter is deployed.
DC-operator detects new task custom resource definition (CRD).
DC-operator iterates one rack at a time.
DC-operator triggers and monitors cleanup operations one pod at a time.
DC-operator reports task progress and status.
User requests a status report of the rolling restart CassandraTask with the kubectl command, and views the status response.

Procedure

Define the restart CassandraTask. This task manifest is in a YAML file, which defines the task and the command in the kind section. The filename for this example is restart-task.cassandratask.yaml.

In order to perform a rolling restart on an entire cluster, you must create a separate restart CassandraTask per datacenter (DC). Restart nodes one datacenter at a time.

Here is a sample:
```
apiVersion: control.k8ssandra.io/v1alpha1
kind: CassandraTask
metadata:
  name: restart-dc
spec:
  datacenter:
    name: dc1
    namespace: demo
  jobs:
    - name: restart-dc1
      command: restart
```
Key options:
- metadata.name: a unique identifer within the Kubernetes namespace where the task is submitted. While the name can be any value, consider including the datacenter name to prevent collision with other options.
- spec.datacenter: a unique namespace and name combination used to determine which datacenter to target with this operation
- spec.jobs[0].command: MUST be restart for this operation
- Optional: spec.jobs[0].args.keyspace_name: restricts this operation to a particular keyspace. Omitting this value results in ALL keyspaces being restarted. By default all keyspaces are rebuilt.
Submit the restart CassandraTask custom resource definition with this kubectl command:
```
kubectl apply -f restart-task.cassandratask.yaml
```
Submit the rebuild CassandraTask object to the Kubernetes cluster where the specified datacenter is deployed.

Review the restart status with this command:

kubectl get cassandratask restart-dc1 | yq .status

Upon completion of the restart task, the DC-level operators update or add the following fields in the CassandraTask YAML file to indicate the status:

either a status.succeeded or status.failed field with a count of the pods that have been restarted and whether each restart was successful or unsuccessful

K8SSAND-1837 issue records an issue with these status fields not being reliably updated.
status.completionTime field: timestamp
status.condition.status: True

status.condition.type: Complete

Sample output:

kind: CassandraTask
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"control.k8ssandra.io/v1alpha1","kind":"CassandraTask","metadata":{"annotations":{},"name":"restart-dc","namespace":"mission-control"},"spec":{"datacenter":{"name":"dc1","namespace":"mission-control"},"jobs":[{"command":"restart","name":"restart-dc1"}]}}
  creationTimestamp: "2022-10-15T21:24:35Z"
  generation: 2
  labels:
    app.kubernetes.io/created-by: cass-operator
    app.kubernetes.io/instance: cassandra-demo
    app.kubernetes.io/managed-by: cass-operator
    app.kubernetes.io/name: cassandra
    app.kubernetes.io/version: 6.8.26
    cassandra.datastax.com/cluster: demo
    cassandra.datastax.com/datacenter: dc1
    control.k8ssandra.io/status: completed
  name: restart-dc
  namespace: mission-control
  ownerReferences:
  - apiVersion: cassandra.datastax.com/v1beta1
    blockOwnerDeletion: true
    controller: true
    kind: CassandraDatacenter
    name: dc1
    uid: 51561d2f-2d20-4a16-b90c-fe9b0655f1ba
  resourceVersion: "780428"
  uid: 2202880f-16f0-4b83-a5ce-ab3057cd6d70
spec:
  concurrencyPolicy: Forbid
  datacenter:
    name: dc1
    namespace: mission-control
  jobs:
  - args: {}
    command: restart
    name: restart-dc1
  restartPolicy: Never
status:
  completionTime: "2022-10-15T21:36:54Z"
  conditions:
  - lastTransitionTime: "2022-10-15T21:36:54Z"
    status: "True"
    type: Complete
  startTime: "2022-10-15T21:24:35Z"