| /* |
| Copyright 2015 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. |
| */ |
| |
| // Package alwayspullimages contains an admission controller that modifies every new Pod to force |
| // the image pull policy to Always. This is useful in a multitenant cluster so that users can be |
| // assured that their private images can only be used by those who have the credentials to pull |
| // them. Without this admission controller, once an image has been pulled to a node, any pod from |
| // any user can use it simply by knowing the image's name (assuming the Pod is scheduled onto the |
| // right node), without any authorization check against the image. With this admission controller |
| // enabled, images are always pulled prior to starting containers, which means valid credentials are |
| // required. |
| package alwayspullimages |
| |
| import ( |
| "io" |
| |
| apierrors "k8s.io/apimachinery/pkg/api/errors" |
| "k8s.io/apimachinery/pkg/util/validation/field" |
| "k8s.io/apiserver/pkg/admission" |
| api "k8s.io/kubernetes/pkg/apis/core" |
| ) |
| |
| // PluginName indicates name of admission plugin. |
| const PluginName = "AlwaysPullImages" |
| |
| // Register registers a plugin |
| func Register(plugins *admission.Plugins) { |
| plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) { |
| return NewAlwaysPullImages(), nil |
| }) |
| } |
| |
| // AlwaysPullImages is an implementation of admission.Interface. |
| // It looks at all new pods and overrides each container's image pull policy to Always. |
| type AlwaysPullImages struct { |
| *admission.Handler |
| } |
| |
| var _ admission.MutationInterface = &AlwaysPullImages{} |
| var _ admission.ValidationInterface = &AlwaysPullImages{} |
| |
| // Admit makes an admission decision based on the request attributes |
| func (a *AlwaysPullImages) Admit(attributes admission.Attributes) (err error) { |
| // Ignore all calls to subresources or resources other than pods. |
| if shouldIgnore(attributes) { |
| return nil |
| } |
| pod, ok := attributes.GetObject().(*api.Pod) |
| if !ok { |
| return apierrors.NewBadRequest("Resource was marked with kind Pod but was unable to be converted") |
| } |
| |
| for i := range pod.Spec.InitContainers { |
| pod.Spec.InitContainers[i].ImagePullPolicy = api.PullAlways |
| } |
| |
| for i := range pod.Spec.Containers { |
| pod.Spec.Containers[i].ImagePullPolicy = api.PullAlways |
| } |
| |
| return nil |
| } |
| |
| // Validate makes sure that all containers are set to always pull images |
| func (*AlwaysPullImages) Validate(attributes admission.Attributes) (err error) { |
| if shouldIgnore(attributes) { |
| return nil |
| } |
| |
| pod, ok := attributes.GetObject().(*api.Pod) |
| if !ok { |
| return apierrors.NewBadRequest("Resource was marked with kind Pod but was unable to be converted") |
| } |
| |
| for i := range pod.Spec.InitContainers { |
| if pod.Spec.InitContainers[i].ImagePullPolicy != api.PullAlways { |
| return admission.NewForbidden(attributes, |
| field.NotSupported(field.NewPath("spec", "initContainers").Index(i).Child("imagePullPolicy"), |
| pod.Spec.InitContainers[i].ImagePullPolicy, []string{string(api.PullAlways)}, |
| ), |
| ) |
| } |
| } |
| for i := range pod.Spec.Containers { |
| if pod.Spec.Containers[i].ImagePullPolicy != api.PullAlways { |
| return admission.NewForbidden(attributes, |
| field.NotSupported(field.NewPath("spec", "containers").Index(i).Child("imagePullPolicy"), |
| pod.Spec.Containers[i].ImagePullPolicy, []string{string(api.PullAlways)}, |
| ), |
| ) |
| } |
| } |
| |
| return nil |
| } |
| |
| func shouldIgnore(attributes admission.Attributes) bool { |
| // Ignore all calls to subresources or resources other than pods. |
| if len(attributes.GetSubresource()) != 0 || attributes.GetResource().GroupResource() != api.Resource("pods") { |
| return true |
| } |
| |
| return false |
| } |
| |
| // NewAlwaysPullImages creates a new always pull images admission control handler |
| func NewAlwaysPullImages() *AlwaysPullImages { |
| return &AlwaysPullImages{ |
| Handler: admission.NewHandler(admission.Create, admission.Update), |
| } |
| } |