/*
Copyright 2016 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// LimitPodHardAntiAffinityTopology admission controller rejects any pod
// that specifies "hard" (RequiredDuringScheduling) anti-affinity
// with a TopologyKey other than kubeletapis.LabelHostname.
// Because anti-affinity is symmetric, without this admission controller,
// a user could maliciously or accidentally specify that their pod (once it has scheduled)
// should block other pods from scheduling into the same zone or some other large topology,
// essentially DoSing the cluster.
// In the future we will address this problem more fully by using quota and priority,
// but for now this admission controller provides a simple protection,
// on the assumption that the only legitimate use of hard pod anti-affinity
// is to exclude other pods from the same node.
package antiaffinity // import "k8s.io/kubernetes/plugin/pkg/admission/antiaffinity"