Add stream metadata

[cgwalters]

Moving a subthread from coreos/fedora-coreos-tracker#98 (comment) (part of openshift/enhancements#201 )here.

Basically let's add https://mirror.openshift.com/dependencies/rhcos/stream-4.8.json

(Note that stream metadata contains multiple architectures by design, so it's not under the existing arch-dependent location).

This could then also be used by coreos-installer download -o rhcos -s rhcos-4.8, and we'd also update all the UPI documentation to refer to it instead of e.g. hardcoding AMIs in the documentation.

Now, we have the option to move this data out of openshift/installer entirely; in connected installs we just download it dynamically, in disconnected installs we require the user to mirror it. I'm on the fence about this; perhaps too big of a change for 4.8.

Proposal: mirror.openshift.com path

• Introduce github.com/openshift/rhel-coreos-bootimage that contains a single stream.json file with multiple branches.
• Add an initially-manual flow to submit a PR there to bump it, that works just like bumping openshift/installer would - e.g. we have CI hooked up
• Add an ART process that scrapes this JSON from git and syncs it to mirror.openshift.com
• Initially also do a manual PR to update openshift/installer

The major disadvantage of this is that we would have bootimages in two places, and the potential for divergence between IPI and UPI. But, I am hopeful that if we streamline CI for rhel-coreos-bootimage we can just wave through sync PRs to update openshift/installer.

It also slightly breaks the "hermetic" nature of the current (openshift-install, release image) tuple because there's another input which can change over time not versioned with those. Perhaps a middle ground compromise is that we add versioned stream metadata, i.e. https://mirror.openshift.com/dependencies/rhcos/stream-4.8-20200325.json and openshift-install has a pinned copy of it.

Proposal: Embed in release image path

• Introduce github.com/openshift/rhel-coreos-bootimage that contains a single stream.json file with multiple branches.
• Add a Dockerfile which puts this JSON in a container image
• Add that container image to the release image
• Change openshift/installer to pull and extract that piece of the release image

Advantages: Makes it more obvious how to get this data "in cluster" for eventual in-cluster updates. Versioned with the release image naturally.
Disadvantages: Nontrivial change to openshift/installer because it has to pull the release image client side (but maybe openshift-installer can just require oc to be present and fork off oc image extract?)

[cgwalters]

For the implementation of this, I think the simplest is probably to directly go from the existing RHCOS cosa metadata and every time we do a build that generates bootimages, update the stream immediately at bootimages.svc. The mirror.openshift.com version would derive from the installer-pinned version.

[bgilbert]

I think the simplest is probably to directly go from the existing RHCOS cosa metadata

To be clear, is the proposal that the stream metadata would be exactly the meta.json? I'd be in favor of using an explicitly designed schema, either the FCOS stream metadata schema or a new one.

[cgwalters]

Oh no the idea is it looks exactly the same as the existing FCOS stream metadata; why would it differ? I'm just saying that we don't create intermediate release.json, i.e. the translation is just cosa meta.json ➡️ stream, right?

[bgilbert]

Ah, okay. As an implementation detail, it might make sense to internally generate an intermediate release.json so we can reuse existing tooling.

[cgwalters]

That said, openshift/enhancements#201 calls for having this as part of the release image. Though...hmm, perhaps the simplest thing is that the installer uploads it as a configmap into the cluster. Now if we decide that this will ultimately be the MCO's job, perhaps it becomes oc -n machine-config-operator configmap/bootimages? Or it could go in oc -n openshift configmap/coreos-bootimages?

But a problem is that doesn't make it easy to get from oc for UPI installs in a way that reliably picks up the same installer-pinned version...which we might want for the "simulate UPI in CI" case. But some UPI installs are going to want to access the mirror.openshift.com data (particularly bare metal), so we could say even e.g. AWS UPI installs should get the AMIs from there, and we do the same for our CI.

But if we do want to implement the oc adm release info --bootimages or whatever...:

"oc adm release new scrapes openshift-install"

First, something like openshift/installer#4102
Then next, we change oc adm release new to explicitly scrape the data out of the installer image and add it to the image it generates (so it's convenient to download). Or we could even try to compress it into container image metadata for the image.

[LorbusChris]

@cgwalters one reason it seemed enticing to me to store the bootimage refs in the payload as opposed to the installer repo was that they wouldn't have to be maintained in the installer repo's rhcos.json (and fcos.json for OKD) in the future.

I nonetheless think having a configmap for the bootimages does make a lot of sense, but why not scrape that data off the payload?