Merge pull request #59293 from roycaihw/openapi_endpoint

Automatic merge from submit-queue (batch tested with PRs 60011, 59256, 59293, 60328, 60367). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Serve OpenAPI spec with single /openapi/v2 endpoint

**What this PR does / why we need it**:
We are deprecating format-separated endpoints (`/swagger.json`, `/swagger-2.0.0.json`, `/swagger-2.0.0.pb-v1`, `/swagger-2.0.0.pb-v1.gz`) for OpenAPI spec, and switching to a single `/openapi/v2` endpoint in Kubernetes 1.10. The design doc and deprecation process are tracked at: https://docs.google.com/document/d/19lEqE9lc4yHJ3WJAJxS_G7TcORIJXGHyq3wpwcH28nU

Requested format is specified by setting HTTP headers

header | possible values
-- | --
Accept | `application/json`, `application/com.github.proto-openapi.spec.v2@v1.0+protobuf`
Accept-Encoding | `gzip`

This PR changes dynamic_client (and kubectl as a result) to use the new endpoint. The old endpoints will remain in 1.10 and 1.11, and get removed in 1.12.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
action required: Deprecate format-separated endpoints for OpenAPI spec. Please use single `/openapi/v2` endpoint instead.
```

/sig api-machinery

Kubernetes-commit: d6153194d929ad6c036d5bbbf67a6f892e75feb5

vendor/k8s.io/api/autoscaling/v1/generated.proto

@@ -44,6 +44,49 @@ message CrossVersionObjectReference {
   optional string apiVersion = 3;
 }
 
+// ExternalMetricSource indicates how to scale on a metric not associated with
+// any Kubernetes object (for example length of queue in cloud
+// messaging service, or QPS from loadbalancer running outside of cluster).
+message ExternalMetricSource {
+  // metricName is the name of the metric in question.
+  optional string metricName = 1;
+
+  // metricSelector is used to identify a specific time series
+  // within a given metric.
+  // +optional
+  optional k8s.io.apimachinery.pkg.apis.meta.v1.LabelSelector metricSelector = 2;
+
+  // targetValue is the target value of the metric (as a quantity).
+  // Mutually exclusive with TargetAverageValue.
+  // +optional
+  optional k8s.io.apimachinery.pkg.api.resource.Quantity targetValue = 3;
+
+  // targetAverageValue is the target per-pod value of global metric (as a quantity).
+  // Mutually exclusive with TargetValue.
+  // +optional
+  optional k8s.io.apimachinery.pkg.api.resource.Quantity targetAverageValue = 4;
+}
+
+// ExternalMetricStatus indicates the current value of a global metric
+// not associated with any Kubernetes object.
+message ExternalMetricStatus {
+  // metricName is the name of a metric used for autoscaling in
+  // metric system.
+  optional string metricName = 1;
+
+  // metricSelector is used to identify a specific time series
+  // within a given metric.
+  // +optional
+  optional k8s.io.apimachinery.pkg.apis.meta.v1.LabelSelector metricSelector = 2;
+
+  // currentValue is the current value of the metric (as a quantity)
+  optional k8s.io.apimachinery.pkg.api.resource.Quantity currentValue = 3;
+
+  // currentAverageValue is the current value of metric averaged over autoscaled pods.
+  // +optional
+  optional k8s.io.apimachinery.pkg.api.resource.Quantity currentAverageValue = 4;
+}
+
 // configuration of a horizontal pod autoscaler.
 message HorizontalPodAutoscaler {
   // Standard object metadata. More info: https://git.k8s.io/community/contributors/devel/api-conventions.md#metadata
@@ -160,6 +203,14 @@ message MetricSpec {
   // to normal per-pod metrics using the "pods" source.
   // +optional
   optional ResourceMetricSource resource = 4;
+
+  // external refers to a global metric that is not associated
+  // with any Kubernetes object. It allows autoscaling based on information
+  // coming from components running outside of cluster
+  // (for example length of queue in cloud messaging service, or
+  // QPS from loadbalancer running outside of cluster).
+  // +optional
+  optional ExternalMetricSource external = 5;
 }
 
 // MetricStatus describes the last-read state of a single metric.
@@ -186,6 +237,14 @@ message MetricStatus {
   // to normal per-pod metrics using the "pods" source.
   // +optional
   optional ResourceMetricStatus resource = 4;
+
+  // external refers to a global metric that is not associated
+  // with any Kubernetes object. It allows autoscaling based on information
+  // coming from components running outside of cluster
+  // (for example length of queue in cloud messaging service, or
+  // QPS from loadbalancer running outside of cluster).
+  // +optional
+  optional ExternalMetricStatus external = 5;
 }
 
 // ObjectMetricSource indicates how to scale on a metric describing a