SIG Scalability has mostly focused on stability and deflaking our tests, investing into framework for writing scalability tests (ClusterLoader v2) with a goal to migrate all tests to it by the end of 2018 and on the work towards extending definition of Kubernetes scalability by providing more/better user-friendly SLIs/SLOs.

### SIG Scheduling

    - [CustomResourceDefinition Defaulting](#customresourcedefinition-defaulting)
    - [CustomResourceDefinition OpenAPI Publishing](#customresourcedefinition-openapi-publishing)
  - [Cluster Lifecycle Stability and Usability Improvements](#cluster-lifecycle-stability-and-usability-improvements)
  - [Continued improvement of CSI](#continued-improvement-of-csi)
    - [Additional Notable Feature Updates](#additional-notable-feature-updates)

- Kube-apiserver: Fixed a `1.27`+ regression in watch stability by serving watch requests without a `resourceVersion` from the watch cache by default, as in <`1.27` (disabling the change in PR 115096 by default). This mitigates the impact of an etcd watch bug (https://github.com/etcd-io/etcd/pull/17555). If the 1.27 change in PR 115096 to serve these requests from underlying storage is still desired despite the impact on watch stability, it can be re-enabled with a `WatchFromStorageWithoutResourceVersion`...

          (o1, o2) ->
              ComparisonChain.start()
                  .compare(o1.iterator.peek(), o2.iterator.peek(), itemComparator)
                  // When elements are equal, use insertion order to maintain stability
                  .compare(o1.index, o2.index)
                  .result();

      queue = new PriorityQueue<>(2, heapComparator);

      int index = 0;

### Bug or Regression

- Fixed a bug where a high churn of events was causing master instability by reducing the maximum number of objects (events) attached to a single etcd lease. ([#100452](https://github.com/kubernetes/kubernetes/pull/100452), [@mborsz](https://github.com/mborsz)) [SIG API Machinery and Instrumentation]

- Kube-apiserver: fixes a 1.27+ regression in watch stability by serving watch requests without a resourceVersion from the watch cache by default, as in <1.27 (disabling the change in #115096 by default). This mitigates the impact of an etcd watch bug (https://github.com/etcd-io/etcd/pull/17555). If the 1.27 change in #115096 to serve these requests from underlying storage is still desired despite the impact on watch stability, it can be re-enabled with a `WatchFromStorageWithoutResourceVersion`...

### Apps

The core workloads API, which is composed of the DaemonSet, Deployment, ReplicaSet, and StatefulSet kinds, has been promoted to GA stability in the apps/v1 group version. As such, the apps/v1beta2 group version is deprecated, and all new code should use the kinds in the apps/v1 group version.

### Auth

- Kube-apiserver: fixes a 1.27+ regression in watch stability by serving watch requests without a resourceVersion from the watch cache by default, as in <1.27 (disabling the change in #115096 by default). This mitigates the impact of an etcd watch bug (https://github.com/etcd-io/etcd/pull/17555). If the 1.27 change in #115096 to serve these requests from underlying storage is still desired despite the impact on watch stability, it can be re-enabled with a `WatchFromStorageWithoutResourceVersion`...

     * empty at any point. (The sum ensures accuracy up through at least 1<<31 per-segment
     * modifications before recheck.)  Method containsValue() uses similar constructions for
     * stability checks.
     */
    long sum = 0L;
    Segment<K, V, E, S>[] segments = this.segments;
    for (int i = 0; i < segments.length; ++i) {
      if (segments[i].count != 0) {
        return false;
      }

  * **beta** PodSecurityPolicy objects limits use of security-sensitive features by pods.
* Kubectl
  * Display line number on JSON errors
  * Add flag -t as shorthand for --tty
* Resources
  * Improved node stability by *optionally* evicting pods upon memory pressure - [Design Doc](https://github.com/kubernetes/kubernetes/blob/release-1.3/docs/proposals/kubelet-eviction.md)