Reconciliation Loop (Old)

1. Update subresource status.conditions (with operator-utils)

Use https://github.com/redhat-cop/operator-utils

Usage:

1. Update Reconciler with:

   import "github.com/redhat-cop/operator-utils/pkg/util"
   
   ...
   type MyReconciler struct {
     util.ReconcilerBase
     Log logr.Logger
     ... other optional fields ...
   }
   

2. Update CRD:

     // +patchMergeKey=type
     // +patchStrategy=merge
     // +listType=map
     // +listMapKey=type
     Conditions []metav1.Condition `json:"conditions,omitempty" patchStrategy:"merge"     patchMergeKey:"type"`
   }
   
   func (m *MyCRD) GetConditions() []metav1.Condition {
     return m.Status.Conditions
   }
   
   func (m *MyCRD) SetConditions(conditions []metav1.Condition) {
     m.Status.Conditions = conditions
   }
   

3. Replace return ctrl.Result{}, err with:

   return r.ManageError(ctx, instance, err)
   

4. Replace return ctrl.Result{}, nil with:

   return r.ManageSuccess(ctx, instance)
   

   1. Object will have conditions:

   kubectl get mysqluser -o yaml
   

   status:
     conditions:
     - lastTransitionTime: "2021-12-28T12:26:21Z"
       message: ""
       observedGeneration: 1
       reason: LastReconcileCycleSucceded
       status: "True"
       type: ReconcileSuccess
   

2. Update subresource status

1. Set mysqluser instance.

   mysqlUser.Status.Phase = "NotReady"
   mysqlUser.Status.Reason = msg
   

   1. Save the instance.

   err := r.Status.Update(ctx, mysqlUser)
   

When updating the status subresource from the client, the StatusWriter must be used. The status subresource is retrieved with Status() and updated with Update() or patched with Patch().

https://sdk.operatorframework.io/docs/building-operators/golang/references/client/#updating-status-subresource

3. Display field in the result of kubectl get (additionalPrinterColumns)

If you don't want to kubebuilder marker, you can write CRD by yourself.

1. Add a column to Status.

    type MySQLStatus struct {
           // INSERT ADDITIONAL STATUS FIELD - define observed state of cluster
           // Important: Run "make" to regenerate code after modifying this file
   +
   +       //+kubebuilder:default=0
   +       UserCount int32 `json:"userCount"`
    }
   

2. Add kubebuilder marker.

    //+kubebuilder:object:root=true
    //+kubebuilder:subresource:status
   +//+kubebuilder:printcolumn:name="UserCount",type="integer",JSONPath=".status.userCount",description="The number of MySQLUsers that belongs to the MySQL"
   
    // MySQL is the Schema for the mysqls API
    type MySQL struct {
   

3. Run make manifests.

        singular: mysql
      scope: Namespaced
      versions:
   -  - name: v1alpha1
   +  - additionalPrinterColumns:
   +    - description: The number of MySQLUsers that belongs to the MySQL
   +      jsonPath: .status.userCount
   +      name: UserCount
   +      type: integer
   +    name: v1alpha1
        schema:
          openAPIV3Schema:
            description: MySQL is the Schema for the mysqls API
   @@ -52,6 +57,13 @@ spec:
                type: object
              status:
                description: MySQLStatus defines the observed state of MySQL
   +            properties:
   +              userCount:
   +                default: 0
   +                format: int32
   +                type: integer
   +            required:
   +            - userCount
                type: object
            type: object
        served: true
   

4. kubectl get

   kubectl get mysql
   NAME           USERCOUNT
   mysql-sample
   

https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#additional-printer-columns

4. Add OwnerReference or SetControllerReference between CustomResources

1. Add SetControllerReference for MySQL

   controllerutil.SetControllerReference(mysql, mysqlUser, r.Scheme)
   err := r.GetClient().Update(ctx, mysqlUser)
   if err != nil {
       return r.ManageError(ctx, mysqlUser, err) // requeue
   }
   

2. Get in yaml format.

   kubectl get mysqluser nakamasato -o yaml
   ...
   metadata:
     ...
     ownerReferences:
     - apiVersion: mysql.nakamasato.com/v1alpha1
       blockOwnerDeletion: true
       controller: true
       kind: MySQL
       name: mysql-sample
       uid: 0689bf66-86a3-40a5-8e50-5e91533a8dc8
     resourceVersion: "928"
     uid: 09c69b78-79c5-4af8-9f84-7eb5dba52371
   ...
   

3. SetControllerReference: Use this when you want to reconcile the owner object on changes to controlled one. > SetControllerReference sets owner as a Controller OwnerReference on controlled. This is used for garbage collection of the controlled object and for reconciling the owner object on changes to controlled (with a Watch + EnqueueRequestForOwner).

   Usually use with the following line in SetupWithManager:

   Owns(&mysqlv1alpha1.MySQLUser{}).
   

   - SetOwnerReference: Use this when you just want garbage collection.

   SetOwnerReference is a helper method to make sure the given object contains an object reference to the object provided. This allows you to declare that owner has a dependency on the object without specifying it as a controller.

5. Finalizer (Handle Cleanup on Deletion of external resource)

Finalizer is set to wait until dependents are deleted before deleting the object.

1. When a new object is created, add the finalizer.
2. When an object is deleted, DeletionTimestamp will be set.
3. Execute the finalizer logic if the finalizer exists.

4. Remove the finalizer.

   Once the list of finalizers is empty, meaning all finalizers have been executed, the resource is deleted by Kubernetes.

5. https://kubernetes.io/blog/2021/05/14/using-finalizers-to-control-deletion/

6. https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#advanced-topics
7. https://book.kubebuilder.io/reference/using-finalizers.html
8. https://sdk.operatorframework.io/docs/building-operators/golang/advanced-topics/#handle-cleanup-on-deletion