Demystifying MeshNetworks when using Multi-Cluster deployments or VMs

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I put this visually to make it easier to talk about these concepts (and even easier to spot misunderstandings).

image
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The configuration shown in the image is applied to the cluster west-cluster; elaborating the points from the image:

  1. The endpoints for the workloads on east-network are retrieved from the registry east-cluster (which has the prerequisite that the secret on how to query the east cluster is already in the istio-system namespace)
  2. To reach the workloads in the east-network network the gateway at the IP 58.23.129.75 will be used. To be more concrete, the CP uses this information to configure workloads in the west-network on how to route traffic to workloads in the east-network
  3. The west-network where the CP is itself installed queries the workload endpoints dynamically from the west-cluster registry (Do we need the secret for west-cluster kubeconfig?).
  4. To reach the workloads on the same network we are pointing to the Ingress Controller istio-ingressgateway ? I picked this example from the docs, and am not sure why is this the case?

Why do we need 4? And did I understand the other points (1-3) correctly?