applicationset proposal

gistfile1.txt

I'm just jotting down a quick idea I had for this project. 

I use ArgoCD and kustomize to manage different environments of microservices. I've been thinking of using this CRD to create an ApplicationSet of my entire stack (in my case 2 namespaces of services) via the git directory generator.

```
apps/
  serviceA/
    argoCD-app.yaml
    base/
      kustomization.yaml
      deployment.yaml
    envs/
      prod/
      staging/
      dev/
  serviceB/
    base/
    envs/
      prod/
      staging/
      dev/
```

My idea is that being able to have a hierarchy of git paths to choose would enable easy to deploy "feature branch" envs that cross service and repo boundaries.

Say my stack is compose of 5 services. And 2 are in active development between 2 teams or a shared feature or something. Each service repo has a branch named `ephemeral/fancy-new-feature`. Using some templating, on first commit via CI my gitops tool duplicates the `/dev` env to `ephemeral/fancy-new-feature`. 

```
spec:
  generators:
  - git:
      repoURL: https://github.com/infra-team/cluster-deployments.git
      directories:
      - path: **/ephemeral/*
 	  - path: **/dev/*
```

```
apps/
  serviceA/
    argoCD-app.yaml
    base/
      kustomization.yaml
      deployment.yaml
    envs/
      prod/
      staging/
      dev/
      ephemeral/
        fancy-new-feature/
  serviceB/
    base/
    envs/
      prod/
      staging/
      dev/
      ephemeral/
        fancy-new-feature/
  serviceC/
    base/
    envs/
      prod/
      staging/
      dev/
  ...
  database/  (ie: deploy a db local to your dev branch but for prod level use external db)
    base/
    envs/
      dev/
```

What I'm proposing is the git directory generator looks for `**/ephemeral/*` and fallsback to `**/dev/*` where `/dev` exists. If either doesn't exist then we don't generate it.

I could see this being useful for a few usecases. Since I use ambassador on a wildcard ingress, I can now expose this feature work to a stakeholder for quick feedback. Perhaps this enables things like telepresense or VScode remote dev server. 

I've been thinking about how to do this via gitops for a while now, I think this CRD may be my answer for a clean solution.