feat: support merge generator

[crenshaw-dev]

fixes #344

[CLAassistant]

All committers have signed the CLA.

[jgwest]

Looks great @crenshaw-dev! Really nice, detailed work 🎉.

Just a couple of requests:

• It would be good to get an E2E test for the merge generator, as we have for the other generators. It should be quick to put it together if you base it on the matrix_e2e_test.go
• Plus some quick tweaks mentioned inline in the review.

(As you said below, the need for nesting makes things a bit convoluted, but that's a necessary evil due to CRD's lack of support for recursion, and our desire to continue to support CRD validation and type definitions.)

[crenshaw-dev]

I'm confused by the build failure. The field which is missing from the committed manifests was recently added (argoproj/argo-cd#7249). But as far as I can tell, it wasn't added to the argo-cd version in go.sum (2.1.0).

Even weirder (to me) is that the logs don't mention downloading argo-cd at all. Guess I need to learn more about go modules.

[jgwest]

@crenshaw-dev Don't worry about it, I think what you have is good, I'll take a look and fix it as needed (probably related to my go.mod bump on master late last week)

[crenshaw-dev]

@jgwest cool, thanks. I still need to add the e2e test, which I should be able to do this afternoon.

[jgwest]

@crenshaw-dev - any luck with this, and/or any issues that you are hitting that I can help with? I'm working on the ApplicationSet v0.3.0 release, and it would be good to get this in if you think that's possible, but no pressure 😄.

[crenshaw-dev]

@jgwest I've been unable to get my e2e test env. working. I'll start a Slack thread. I'm sure I'm missing something simple. :-)

[jgwest]

@crenshaw-dev One other issue I've noticed is that the ApplicationSet controller install YAML can no longer be applied; I see now why you changed the install script from kubectl create to kubectl apply.., with the error being "The CustomResourceDefinition "applicationsets.argoproj.io" is invalid: metadata.annotations: Too long: must have at most 262144 bytes"

[crenshaw-dev]

@jgwest yep... I'll double-check that there's no documentation which requires apply instead of create.

[crenshaw-dev]

@jgwest added e2e tests. You'll probably also want to glance at the docs commit.

[crenshaw-dev]

Looks like the doc lint error is a cert issue on kustomize.io. My guess is they'll fix the cert soon. Probably safe to ignore the error.

[jgwest]

@crenshaw-dev -

Switching from kubectl apply to kubectl create has a few major issues:

• It makes upgrade more difficult: we would need to ask the user to kubectl delete && kubectl create their application set install, vs the current model which is an in-place upgrade with apply. The in-place apply is how both applicationset controller and Argo CD work now.
  • I'm not even sure if it's possible to delete a CRD if there are CRs that are still using it? IIRC I've seen mixed results here in the past. It means, to upgrade, you might need to delete all the ApplicationSet CRs as well.
• As you are aware, we are working on merging ApplicationSet controller into Argo CD. So this change would also affect Argo CD, because the ApplicationSet CR would now be a part of the Argo CD install yaml. Thus we would require Argo CD users to kubectl delete && kubectl create upgrade Argo CD using the create/delete approach as well.

@alexmt have y'all hit this with Argo CD CR, and/or any suggestions? This would unfortunately affect Argo CD as wel,l if we were to combine argo cd/appset install YAMLs.

[crenshaw-dev]

I'm a bit ignorant of the subtleties here... Couldn't a user perform a non-disruptive upgrade using kubectl replace?

[jgwest]

LGTM, thanks again @crenshaw-dev, great work.

(And thanks @leoluz for reviewing!)