feat: Direct connection support between provider clusters

[Gabbe64]

Description

Fixes #3011

This PR introduces the possibility to make pods deployed on provider clusters communicate directly by using an established network connection (liqoctl network connect).

This feature is opt-in: users can enable it by adding the annotation key use-direct-connections: true to the Service exposing the pods that should communicate directly. This way, the default behavior remains unchanged, while also giving users the possibility to choose whether to route traffic through the consumer cluster or directly.

Implementation

As discussed during the last community meetings, the modified components are the virtual-kubelet and the ShadowEndpointslice controller.

Transmission - virtual-kubelet

When reflecting Endpointslices and the corresponding Service has the right annotation, some data is collected from the informers (without direct the API server calls) then serialized as JSON and reflected in the annotation field of the ShadowEndpointslice.

This data is:

1. The clusterID where the endpoint is deployed,
2. The local IPs contained in the Endpointslice of the consumer,
3. The same IPs, remapped by the consumer cluster.

Reception

The ShadowEndpointslice controller (in the provider cluster) receives this data and uses it to remap the addresses so to use the direct connections towards other provider clusters (if available).

To achieve this:

• Endpoints leading to pods on a different provider are identified using point 3.
• They are replaced with direct addresses, derived from the remote cluster’s podCIDR (point 1) and the host part extracted from the local IP (point 2); this required the implementation of a "forced mapping".

[adamjensenbot]

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[cheina97]

/test

[aleoli]

/test