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Introduce an interface for controllers to improve consistency #3263

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Introduce an interface for controllers to improve consistency #3263

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Commits on Nov 9, 2023

  1. operator: Let AROControllers configure their own loggers 

    Progressing toward not exporting controller name constants.
    Matthew Barnes committed Nov 9, 2023
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  2. operator: Introduce AROReconciler interface 

    Initial methods are geared toward controller registration:

	GetName() string
	SetupWithManager(ctrl.Manager) error

All AROController subtypes must implement SetupWithManager.
    Matthew Barnes committed Nov 9, 2023
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  3. operator: Do not export controller name constants 

    Use AROReconciler.GetName instead.
    Matthew Barnes committed Nov 9, 2023
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  4. operator: Consistency tweaks

    Matthew Barnes committed Nov 9, 2023
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  5. operator: Add EnabledFlag field to AROController

    Matthew Barnes committed Nov 9, 2023
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  6. operator: Add reconcile methods to AROReconciler interface 

    This introduces two new methods in AROReconciler:

  ReconcileEnabled(ctx, request, cluster) -> (result, error)
  ReconcileDisabled(ctx, request, cluster) -> (result, error)

One or the other method will be called based on the controller's
"enabled" operator flag.

AROController itself now implements the Reconcile method in order
to consistently handle disabled controllers.  Subtypes need only
implement the ReconcileEnabled method, called when the controller
is enabled.

The Reconcile method uses the "template method" design pattern
from object-oriented programming.  This warrants some explanation
since the pattern looks a little odd in Golang.

Some background reading:
https://golangbyexample.com/template-method-design-pattern-golang/

AROController provides ReconcileDisabled but leaves ReconcileEnabled
unimplemented, so ReconcileEnabled is effectively an abstract method.
Therefore AROController itself is not an AROReconciler according to
Golang's interface semantics, but its subtypes are.

Because AROController's Reconcile method calls ReconcileEnabled,
which is abstract, it needs a way to cast itself to an AROReconciler.

This is the purpose of the Reconciler field in AROController.  The
field is set during subtype instantiation:

   r := ExampleReconciler{
       AROController: base.AROController {
           Log:         ...
           Client:      ...
           Name:        ...
           EnabledFlag: ...
       }
   }
   r.Reconciler = r
   return r

The Reconciler field is essentially a virtual method table like
those inherent in polymorphic languages like C++ and Python.  It
allows AROController to call abstract AROReconciler methods that
are implemented by a subtype.
    Matthew Barnes committed Nov 9, 2023
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  7. operator: Add unit tests for AROController's Reconcile

    Matthew Barnes committed Nov 9, 2023
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