Merge pull request #95 from salasberryfin/out-of-cluster-adr

ADR: Running out of Rancher Manager cluster

docs/adr/0004-running-out-of-rancher-manager-cluster.md

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+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+**Table of Contents**  *generated with [DocToc](https://github.com/thlorenz/doctoc)*
+
+- [4. Running out of Rancher Manager cluster](#4-running-out-of-rancher-manager-cluster)
+  - [Context](#context)
+  - [Decision](#decision)
+  - [Consequences](#consequences)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+
+# 4. Running out of Rancher Manager cluster
+
+* Status: proposed
+* Date: 2023-08-31
+* Authors: @salasberryfin
+* Deciders: @richardcase @alexander-demicev @furkatgofurov7 @Danil-Grigorev @mjura
+
+## Context
+
+As an operator, I want the choice to deploy Rancher Turtles in the same or a 
+different cluster to Rancher Manager, so that I have a choice in my deployment 
+topology.
+
+## Decision
+
+`CAPIImportReconciler` will contain two differentiated clients:
+- `Client`: in-cluster client for the controller and the CAPI resources.
+- `RancherClient`: for the Rancher Manager cluster.
+
+A flag `rancher-kubeconfig` with a path to a kubeconfig file is used to select 
+the type of installation:
+- If no value is passed, Rancher Turtles is set to the same cluster 
+installation: `Client` and `RancherClient` are the same instance of the client.
+- If a valid path to a kubeconfig file is passed, `RancherClient` is set to 
+client created from the kubeconfig.
+
+From an end-user perspective:
+
+* No parameter is required if Rancher Manager and Rancher Turtles run in the 
+same cluster.
+* User will provide a path to a valid kubeconfig file that is available in the 
+pod if installing Rancher Turtles outside of Rancher Manager cluster.
+
+## Consequences
+
+- The path to the kubeconfig must be mounted in the pod to be accessible. This 
+pattern is aligned with what is used in [controller-runtime](https://github.com/kubernetes-sigs/controller-runtime/blob/964a416cf5acf5a67bdc5904897006447ac11509/pkg/client/config/config.go#L60).