OpenShift 4.15.0 cluster

https://docs.openshift.com/

Mandatory, A running OpenShift cluster instance.

Helm

https://helm.sh/docs/intro/install

Mandatory, the version depends on the Kubernetes instance version on which the product is deployed. 

Please refer to Helm version support page below for further details.
https://helm.sh/docs/topics/version_skew/

Cert-manager 1.1.0 or later

https://cert-manager.io

Recommended

Note, if you do not want to use cert-manager, there is an option to do the Helm install with the parameter operator.webhook.tls.cert.delegate=internal . Search for documented helm values to understand the implications of this.

kubectl

https://kubernetes.io/docs/tasks/tools/install-kubectl/

Mandatory, for all administrative tasks with the cluster