Define and document KIM architecture

[tobiscr]

Description

KIM will become a critical component of the Kyma backend and be responsible for any infrastructure (especially cluster creation) related tasks.

We see already a growing amount of expectations and requirements for KIM. This requires a well defined architecture which supports

• easy extensibility (e.g. any value of the shoot-spec should be configurable by customer values or use default config values as fallback)
• good testability (e.g. mock the Gardener API to simulate any possible use-case in unit- or E2E-tests)
• well performing (e.g. KIM has to be able to manage 10.000 clusters with an linear scaling processing time)
• comprehensive monitoring (e.g. central KPIs of KIM have to be exposed, e.g. failure rate, processing time, throughput, resource consumption)
• acceptable maintainability efforts (e.g. most of the identified incidents can be covered by the software/architecture without human intervention)

Take already known requirements into consideration when designing the new architecture:

• Limited cluster infrastructure control to Gardener based Kyma clusters for end users [EPIC] kyma#13153
• Expose Auditlog configuration
• Customizable OIDC configuration
• Helm broker doesn't deploy functions properly kyma#126
• Configurable networking filter for ingress traffic (geo-blocking) [EPIC] #136

AC:

• Create ADRs for KIM which show how the software architecture will look like

  • Add to each ADR a table and evaluate how good/bad the non-functional requirements (see list above) are supported
  • Present the results of the ADR and evaluation to @kyma-project/framefrog

• When ADR is merged, close following issues:

  • Prepare a plan for migration from current GardenerCluster CR to new Kubeconfig CRs #187
  • Create proposal for Cluster CR we expect from KEB #125

• Implement a POC of the ADR and demonstrate it to the team - PoC that creates gardener cluster when CR is created akgalwas/infrastructure-manager#1

[Disper]

We might have some overlap with https://github.com/kyma-project/kyma-environment-broker/blob/main/docs/user/01-10-architecture.md

[Disper]

Closing, as the ADR was merged.