mirror of https://github.com/k3s-io/k3s
80 lines
2.9 KiB
Markdown
80 lines
2.9 KiB
Markdown
# Kubernetes Proposal - Admission Control
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**Related PR:**
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| Topic | Link |
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| ----- | ---- |
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| Separate validation from RESTStorage | https://github.com/GoogleCloudPlatform/kubernetes/issues/2977 |
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## Background
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High level goals:
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* Enable an easy-to-use mechanism to provide admission control to cluster
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* Enable a provider to support multiple admission control strategies or author their own
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* Ensure any rejected request can propagate errors back to the caller with why the request failed
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Authorization via policy is focused on answering if a user is authorized to perform an action.
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Admission Control is focused on if the system will accept an authorized action.
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Kubernetes may choose to dismiss an authorized action based on any number of admission control strategies.
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This proposal documents the basic design, and describes how any number of admission control plug-ins could be injected.
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Implementation of specific admission control strategies are handled in separate documents.
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## kube-apiserver
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The kube-apiserver takes the following OPTIONAL arguments to enable admission control
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| Option | Behavior |
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| ------ | -------- |
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| admission_control | Comma-delimited, ordered list of admission control choices to invoke prior to modifying or deleting an object. |
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| admission_control_config_file | File with admission control configuration parameters to boot-strap plug-in. |
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An **AdmissionControl** plug-in is an implementation of the following interface:
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```go
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package admission
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// Attributes is an interface used by a plug-in to make an admission decision on a individual request.
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type Attributes interface {
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GetNamespace() string
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GetKind() string
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GetOperation() string
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GetObject() runtime.Object
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}
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// Interface is an abstract, pluggable interface for Admission Control decisions.
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type Interface interface {
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// Admit makes an admission decision based on the request attributes
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// An error is returned if it denies the request.
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Admit(a Attributes) (err error)
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}
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```
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A **plug-in** must be compiled with the binary, and is registered as an available option by providing a name, and implementation
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of admission.Interface.
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```go
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func init() {
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admission.RegisterPlugin("AlwaysDeny", func(client client.Interface, config io.Reader) (admission.Interface, error) { return NewAlwaysDeny(), nil })
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}
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```
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Invocation of admission control is handled by the **APIServer** and not individual **RESTStorage** implementations.
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This design assumes that **Issue 297** is adopted, and as a consequence, the general framework of the APIServer request/response flow
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will ensure the following:
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1. Incoming request
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2. Authenticate user
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3. Authorize user
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4. If operation=create|update, then validate(object)
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5. If operation=create|update|delete, then admission.Admit(requestAttributes)
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a. invoke each admission.Interface object in sequence
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6. Object is persisted
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If at any step, there is an error, the request is canceled.
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