Hardcoded HOST_IP in agent-injector does not work on fresh clusters.

[simonostendorf]

Describe the bug

Currently the Agent Injector Pod Template has a hardcoded env var HOST_IP that is used to inject the status.hostIP into the container.
This value does not exist on a fresh cluster without a cloud-controller-manager installed. This results in a Init:CreateContainerConfigError error.

This is pretty bad because vault-agent-injector cannot be used to provide secrets for the cloud-controller-manager (anymore).

To Reproduce
Steps to reproduce the behavior:

1. Create new Kubernetes cluster and dont install anything (e.g. using 1.32.1)
2. Node has no internal or external ip set because its waiting for the cloud-controller-manager
3. Install vault-agent-injector
4. Install cloud-controller-manager with vault injection annotations
5. Pod fails with Init:CreateContainerConfigError error because HOST_IP cannot be set because there is no host ip

Expected behavior

I think it would be good to make this optional (if its possible) or allow specification of injection templates or if the variable is not used inside the agent-injector it could be removed.

Environment

• Kubernetes version: kubeadm 1.32.1
• vault-k8s version: 1.18.1

Additional context

none