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Use Cases Affecting the Roadmap for PoC2023q1


The outline mentions features that need not be implement at first. In the following sections we consider some particular use cases.


MVI needs customization. We can demo an MVI scenario without: self-sufficient edge clusters, summarization, upsync (Return and/or summarization of reported state from associated objects), sophisticated handling of workload conflicts.

What about denaturing?


I am not sure what is workable here. Following are some possibilities. They vary in two dimensions.

How C2P controller consumes reports#

Through view of workload APIExport and workload APIBindings#

As outlined in PR 241: - the C2P team maintains CRDs, APIResourceSchemas, and an APIExport for the policy and report resources; - the C2P team puts those APIResourceSchemas and that APIExport in a kcp workspace of their choice; - the workload management workspace has an APIBinding to that APIExport; - the EdgePlacement selects that APIBinding for downsync; - the APIBinding goes to the mailbox workspace but not the edge cluster; - those CRDs are pre-installed on the edge clusters; - the APIExport's view shows the report objects in the mailbox workspaces (as well as anywhere else they exist).

This is not a great choice because of "those CRDs are pre-installed on the edge clusters".

It is also not a great choice because it requires the C2P team to maintain two copies of the Kyverno resource definitions.

This is a bad choice because it is not consistent with the preferred way to demonstrate installation of Kyverno, which is to have Helm install Kyverno into the workload management workspace.

Through a new kind of view#

We could define a new kind of view that does what we want.

Through view of EMC APIExport and mailbox APIBindings#

This approach also uses APIExport and APIBinding objects but in a different way than above. In this approach the placement translator maintains one APIExport in the edge service provider workspace and a corresponding APIBinding object in each mailbox workspace, and they work together as follows.

The APIExport has an empty LatestResourceSchemas but a large dynamic PermissionClaims slice. In particular, there is a PermissionClaim for every resource involved in downsync or upsync in any EdgePlacement object. Some day we might try something more granular, but today is not that day.

In each mailbox workspace, the corresponding APIBinding's list of accepted PermissionClaims has an entry for every resource downsynced or upsynced to that workspace.

As a consequence, the APIExport's view holds all the objects whose kind/resource is defined by those APIBindings.

Through an API for consuming from mailboxes#

The C2P Controller uses the API proposed in PR 240 to read the report objects from the mailbox workspaces. This has the downside of exposing the mailbox workspaces as part of the KubeStellar interface --- which they were NOT originally intended to be.

C2P Controller consumes report summaries prepared by KubeStellar#

In this scenario: - we have defined and implemented summarization in KubeStellar; - that summarization is adequate for the needs of the C2P Controller; - that controller consumes summaries rather than the reports themselves.

Mailbox vs. Edge#

The latest plan is to use full EMC.

Using the current TMC syncer#

In this scenario the edge clusters are not self-sufficient; the workload containers in an edge cluster use kube api services from the corresponding mailbox workspace. The key insight here is that from an outside perspective, a pair of (edge cluster, corresponding mailbox workspace) operates as a unit and the rest of the world does not care about internal details of that unit. But that is only true if you do not require too much from the networking. In this scenario, a workload container runs in the edge cluster and a workload Service object is about proxying/load-balancing in the edge cluster. An admission control webhook normally directs the apiserver to call out to a virtual IP address associated with a Service; that is a problem in this scenario because the apiserver in question is the one holding the mailbox workspace but the Service that gets connections to the workload containers is in the edge cluster. This scenario will work if the C2P workload does not include admission control webhooks. Note that Kubernetes release 1.26 introduces CEL-based validating admission control policies, so using them would not involve webhooks.

Expand TMC to support webhooks#

The problem with webhooks would go away if TMC were expanded to support them, perhaps through some sort of tunneling so that a client in the center can open connections to a Service at the edge.

Pre-deploy controllers and resources on edge clusters#

In this scenario, the PVP/PEP is pre-deployed on the edge clusters, and the policy and report resources (which are cluster-scoped) are predefined there too. This scenario would continue to use the TMC syncer, but only need it to downsync the policies and upsync the reports.

Use full EMC#

No shortcuts here, no limitations.