This version ships Redis with persistence (AOF) activated. As this component is used as a message broker and not as a cache, the previous redis deployment can be removed before lauching the upgrade.
No task should be running on the clusters, then, for each cluster where substra-backend is deployed, run the following command before upgrading:
kubectl delete statefulsets BACKEND_NAME-redis-master -n NS_NAME, where:
BACKEND_NAME is the release name as defined in Helm
NS_NAME the namespace name where your pods are deployed