Is it possible to upgrade the service version via Helm if the previous version was installed via kubectl apply, without deleting the application?

You cannot directly update an application through Helm if it was initially installed using kubectl apply without deleting the application. The reason is that Helm manages resources through its own release mechanism and stores the state in a ConfigMap or Secret within the cluster. If resources are created manually (kubectl apply), Helm is unaware of them and cannot manage them.

To switch to Helm management without deleting the application, you can:

• Create a Helm chart that describes the current state of the application.
• Use helm import (if available) or manually synchronize resources with Helm.
• Or delete the manually created resources and then install the application via Helm.

In general, for proper management and updates through Helm, it is recommended to initially install the application using Helm.