Promote Parallel Image Pull Limit to Beta

Signed-off-by: ruiwen-zhao <ruiwen@google.com>

keps/sig-node/3673-kubelet-parallel-image-pull-limit/README.md

@@ -385,6 +385,7 @@ A new node_e2e test with  `serialize-image-pulls==false` will be added to make s
 
 #### Beta
 - Gather feedback from developers and surveys
+- Add e2e test to cover the parallel image pull case
 
 #### GA
 - Gather feedback from real-world usage from kubernetes vendors.
@@ -585,6 +586,7 @@ https://github.com/kubernetes/kubernetes/pull/97058/files#diff-7826f7adbc1996a05
 This section must be completed when targeting beta to a release.
 -->
 
+
 ###### How can a rollout or rollback fail? Can it impact already running workloads?
 
 <!--
@@ -597,13 +599,19 @@ rollout. Similarly, consider large clusters and how enablement/disablement
 will rollout across nodes.
 -->
 
+This is an opt-in feature, and it does not change any default behavior. If there is any bug in this feature, image pulls might fail.
+No running workloads will be imapcted.
+
 ###### What specific metrics should inform a rollback?
 
 <!--
 What signals should users be paying attention to when the feature is young
 that might indicate a serious problem?
 -->
 
+In worst case, image pulls might fail. Users can monitor image pull k8s events and `runtime_operations_errors_total` metric to see if there is an increase
+of image pull failures. 
+
 ###### Were upgrade and rollback tested? Was the upgrade->downgrade->upgrade path tested?
 
 <!--
@@ -612,12 +620,18 @@ Longer term, we may want to require automated upgrade/rollback tests, but we
 are missing a bunch of machinery and tooling and can't do that now.
 -->
 
+This is an opt-in feature, and it does not change any default behavior. We manually tested enabling and disabling this feature by changing kubelet config and
+restarting kubelet.
+
+
 ###### Is the rollout accompanied by any deprecations and/or removals of features, APIs, fields of API types, flags, etc.?
 
 <!--
 Even if applying deprecation policies, they may still surprise some users.
 -->
 
+No.
+
 ### Monitoring Requirements
 
 <!--
@@ -635,6 +649,8 @@ checking if there are objects with field X set) may be a last resort. Avoid
 logs or events for this purpose.
 -->
 
+See the section below.
+
 ###### How can someone using this feature know that it is working for their instance?
 
 <!--
@@ -646,13 +662,10 @@ and operation of this feature.
 Recall that end users cannot usually observe component logs or access metrics.
 -->
 
-- [ ] Events
-  - Event Reason:
-- [ ] API .status
-  - Condition name:
-  - Other field:
-- [ ] Other (treat as last resort)
-  - Details:
+- [X] Events
+  - Event Reason: Pulling
+
+This feature sets a limit on the parallel image pulls, so an operator can look at image pull k8s events, and see the number of images pulled at the same time.
 
 ###### What are the reasonable SLOs (Service Level Objectives) for the enhancement?
 
@@ -677,15 +690,19 @@ question.
 Pick one more of these and delete the rest.
 -->
 
-- [ ] Metrics
-  - Metric name:
-  - [Optional] Aggregation method:
+We can rely on the existing metrics on image pull to determine if this feature has any impact on image pulling. 
+
+- [X] Metrics
+  - Metric name: runtime_operations_errors_total
+  - [Optional] Aggregation method: operation_type=pull_image
   - Components exposing the metric:
 - [ ] Other (treat as last resort)
   - Details:
 
 ###### Are there any missing metrics that would be useful to have to improve observability of this feature?
 
+No.
+
 <!--
 Describe the metrics themselves and the reasons why they weren't added (e.g., cost,
 implementation difficulties, etc.).
@@ -699,6 +716,8 @@ This section must be completed when targeting beta to a release.
 
 ###### Does this feature depend on any specific services running in the cluster?
 
+No.
+
 <!--
 Think about both cluster-level services (e.g. metrics-server) as well
 as node-level agents (e.g. specific version of CRI). Focus on external or
@@ -817,8 +836,12 @@ details). For now, we leave it here.
 
 ###### How does this feature react if the API server and/or etcd is unavailable?
 
+N/A. This feature does not rely on any component other than kubelet.
+
 ###### What are other known failure modes?
 
+No known failure modes.
+
 <!--
 For each of them, fill in the following information by copying the below template:
   - [Failure mode brief description]
@@ -834,6 +857,9 @@ For each of them, fill in the following information by copying the below templat
 
 ###### What steps should be taken if SLOs are not being met to determine the problem?
 
+If this feature impact image pulling. The user should unset MaxParallelImagePulls (i.e. setting MaxParallelImagePulls to nil), 
+or set SerialImagePulls to true to enable serial image pulling.
+
 ## Implementation History
 
 <!--
@@ -847,6 +873,10 @@ Major milestones might include:
 - when the KEP was retired or superseded
 -->
 
+### Alpha
+
+Alpha feature was implemented in 1.27.
+
 ## Drawbacks
 
 <!--