feat: Allow templating in GlobalTenantResource and TenantResource

[h4wkmoon]

Describe the feature

It would be nice to allow some templating in GlobalTenantResource and TenantResource. For now, I can see 2 variables that could be templated: the tenant name, and the namespace name.

We have a use-case where we want to deploy an ingress in specific namespaces for specific tenants. The hostname of the ingress has the tenant name in it.

What would the new user story look like?

As a cluster-admin, I would like to be able to use tenant name, and namespace name in the manifest of resource generated by globaltenantresources.
As a tenant owner, I would like to be able to use tenant name, and namespace name in the manifest of resource generated by tenantresources.

Expected behavior

This resource would create an ingress with the interpolated hostname.
Double curly brackets is just a proposal. Any other templating synthax may be ok. Kyverno has similar features. It can be used as an example.

apiVersion: capsule.clastix.io/v1beta2
kind: GlobalTenantResource
metadata:
  name: some-ingress
spec:
  tenantSelector:
    matchLabels:
      somelabel: "somevalue"
  resyncPeriod: 60s
  resources:
    - namespaceSelector:
        matchLabels:
          somelabel: "somevalue"
      rawItems:
      - apiVersion: networking.k8s.io/v1
        kind: Ingress
        metadata:
          name: something
        spec:
          rules:
          - host: something.{{tenant_name}}.mydomain
            [...]

[prometherion]

This could be done, thanks for sharing your proposal!

I'd say we should stick to the Go templating guidelines, so curly brackets as delimitators are good.

I was thinking something like as:

• {{ tenant.name }} for the given Tenant Name
• {{ namespace }} for the Namespace where the resource will be deployed

Any other ones that could be helpful?

Keep in mind that we can just support templating for rawItems, at the current state.

[h4wkmoon]

Nothing else comes to my mind.
Thx.

[aslafy-z]

@prometherion Wouldn't it be nice to get the whole Tenant object into the templating engine? So we can use {{ tenant.metadata.name}} and access all the other fields? I don't have a real use case for it as of now.

[prometherion]

Wouldn't it be nice to get the whole Tenant object into the templating engine?

"With great power comes great responsibility", and templating is so error-prone and I think we should stick to simplicity.

If there's a real and documented use-case for further templating, we can talk, I'm totally open to it.