Add Job finalizer in creation strategy

Then, the finalizer can be used by the job controller to determine if the Job should be tracked with finalizers.
There is no longer need for a distinction between empty struct and nil.

Signed-off-by: Aldo Culquicondor <[email protected]>

Author: alculquicondor

keps/sig-apps/2307-job-tracking-without-lingering-pods/README.md

@@ -153,7 +153,8 @@ type JobStatus struct {
 
     // UncountedTerminatedPods holds UIDs of Pods that have finished but
     // haven't been accounted in the counters.
-    // If nil, Job tracking doesn't make use of this structure.
+    // Old jobs might not be tracked using this field, in which case this
+    // field remains null.
     // +optional
     UncountedTerminatedPods *UncountedTerminatedPods
 }
@@ -179,8 +180,8 @@ could be stopped at any point and executed again from the first step without
 losing information. Generally, all the steps happen in a single Job sync
 cycle.
 
-0. The Job controller adds a the `batch.kubernetes.io/job-completion` finalizer
-   to the Job.
+0. kube-apiserver adds the `batch.kubernetes.io/job-completion` finalizer
+   to newly created Jobs.
 1. The Job controller calculates the number of succeeded Pods as the sum of:
    - `.status.succeeded`,
    - the size of `job.status.uncountedTerminatedPods.succeeded` and
@@ -329,19 +330,22 @@ time, the cluster can have Jobs whose Pods don't have the
 `batch.kubernetes.io/job-completion` finalizer. It would be hard to add the
 finalizer to all Pods while preventing race conditions.
 
-We use `.status.uncountedTerminatedPods != nil` to indicate whether the Job
-was created after the feature was enabled. If this field is nil, the Job
-controller tracks Pods using the legacy tracking.
+The job controller uses the existence of the finalizer
+`batch.kubernetes.io/job-completion` to determine if it should use tracking with
+finalizers. If the finalizer is not present, and the Job is not yet completed,
+the job controllers tracks Pods using the legacy tracking (with lingering Pods).
 
-The kube-apiserver sets `.status.uncountedTerminatedPods` to an empty struct
-when the feature gate `JobTrackingWithFinalizers` is enabled, at Job
-creation.
+The kube-apiserver sets the `batch.kubernetes.io/job-completion` finalizer to
+newly created Jobs when the feature gate `JobTrackingWithFinalizers` is enabled.
 
 When the feature is disabled after being enabled for some time, the next time
 the Job controller syncs a Job:
-1. It removes finalizers from all Pods owned by the Job.
+1. It removes finalizers from the Job and all the Pods owned by it.
 2. Sets `.status.uncountedTerminatedPods` to nil.
 
+After this point, the Job will no longer be tracked using finalizers, even if
+the feature gate is re-enabled.
+
 ### Version Skew Strategy
 
 No implications to node runtime.
@@ -476,8 +480,8 @@ previous answers based on experience in the field._
     - estimated throughput: one per Pod created by the Job controller, when Pod
       finishes or is removed.
     - originating component: kube-controller-manager
-  - PATCH Jobs, to add and remove finalizers.
-    - estimated throughput: two calls for each Job created.
+  - PATCH Jobs, to remove finalizers.
+    - estimated throughput: one call for each Job created.
     - originating component: kube-controller-manager
   - PUT Job status, to keep track of uncounted Pods.
     - estimated throughput: at least one per Job sync. The job controller