Upgrade a DataStax Enterprise (DSE) cluster With Zero Downtime

Apply and deploy a new version of DataStax Enterprise (DSE) to an existing cluster. Modify the MissionControlCluster manifest, updating the DSE version from 6.8.25 to 6.8.26.

Prerequisites

A prepared environment on either bare-metal/VM or an existing Kubernetes cluster.

Example

The existing deployment consists of 1 datacenter (dc1) with 3 nodes, each node on a separate rack.

Workflow of user and operators

User submits a modified MissionControlCluster manifest to the Control Plane Kubernetes cluster.
Cluster-level operator detects the change and modifies the datacenter-level resource.
Datacenter-level operator detects the change and modifies the rack-level resource.
Datacenter-level operator terminates the instance in the rack.
Datacenter-level operator bootstraps a replacement node.
Datacenter-level operator repeats steps c-e for all racks in one datacenter.
Cluster-level operator repeats steps b-e for all datacenters in a cluster, one dc at a time, in the case of a multi-datacenter cluster.
User follows Upgrade SSTables steps, if required.

Upgrades of DataStax Enterprise (DSE) versions follow the same process as configuration change deployments. See Deploying Configuration Changes to a DataStax Enterprise (DSE) Cluster.

Cluster upgrade with ZDM

Modify the existing MissionControlCluster YAML (demo.yaml) in the Control Plane Kubernetes cluster, overwriting the value 6.8.25 in the spec.k8ssandra.cassandra.serverVersion field with 6.8.26:
```
apiVersion: missioncontrol.datastax.com/v1beta1
kind: MissionControlCluster
metadata:
  name: demo
spec:
  k8ssandra:
    cassandra:
      serverVersion: 6.8.26
...
```
Submit the version change to the Kubernetes Control Plane cluster with the following command:
```
kubectl apply -f demo.yaml
```
The DSE version upgrade is done as a rolling update.
Monitor the progress of the upgrade from the Data Plane east cluster, looking at the status of the CassandraDatacenter with this command:
```
kubectl get cassandradatacenter dc1 -o yaml
```
Sample results
status: cassandraOperatorProgress: Updating conditions: - lastTransitionTime: "2022-10-20T16:07:10Z" message: "" reason: "" status: "True" type: Healthy - lastTransitionTime: "2022-10-20T16:07:10Z" message: "" reason: "" status: "False" type: Stopped ...
The Updating conditions:status field value of "True" indicates that the update is in progress. Upon completion of the Updating operation, the Cass-Operator changes the Updating conditions.status field value to "False".

What’s next

Users may trigger an Upgrade SSTables operation to rewrite SSTables into newer formats, if required.