mirror of https://github.com/k3s-io/k3s
375 lines
13 KiB
Markdown
375 lines
13 KiB
Markdown
<!-- BEGIN MUNGE: UNVERSIONED_WARNING -->
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<!-- BEGIN STRIP_FOR_RELEASE -->
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<img src="http://kubernetes.io/img/warning.png" alt="WARNING"
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width="25" height="25">
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<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
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If you are using a released version of Kubernetes, you should
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refer to the docs that go with that version.
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<!-- TAG RELEASE_LINK, added by the munger automatically -->
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<strong>
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The latest release of this document can be found
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[here](http://releases.k8s.io/release-1.1/docs/design/namespaces.md).
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Documentation for other releases can be found at
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[releases.k8s.io](http://releases.k8s.io).
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</strong>
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--
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<!-- END STRIP_FOR_RELEASE -->
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<!-- END MUNGE: UNVERSIONED_WARNING -->
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# Namespaces
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## Abstract
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A Namespace is a mechanism to partition resources created by users into
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a logically named group.
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## Motivation
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A single cluster should be able to satisfy the needs of multiple user communities.
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Each user community wants to be able to work in isolation from other communities.
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Each user community has its own:
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1. resources (pods, services, replication controllers, etc.)
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2. policies (who can or cannot perform actions in their community)
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3. constraints (this community is allowed this much quota, etc.)
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A cluster operator may create a Namespace for each unique user community.
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The Namespace provides a unique scope for:
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1. named resources (to avoid basic naming collisions)
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2. delegated management authority to trusted users
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3. ability to limit community resource consumption
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## Use cases
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1. As a cluster operator, I want to support multiple user communities on a single cluster.
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2. As a cluster operator, I want to delegate authority to partitions of the cluster to trusted users
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in those communities.
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3. As a cluster operator, I want to limit the amount of resources each community can consume in order
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to limit the impact to other communities using the cluster.
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4. As a cluster user, I want to interact with resources that are pertinent to my user community in
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isolation of what other user communities are doing on the cluster.
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## Design
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### Data Model
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A *Namespace* defines a logically named group for multiple *Kind*s of resources.
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```go
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type Namespace struct {
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TypeMeta `json:",inline"`
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ObjectMeta `json:"metadata,omitempty"`
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Spec NamespaceSpec `json:"spec,omitempty"`
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Status NamespaceStatus `json:"status,omitempty"`
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}
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```
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A *Namespace* name is a DNS compatible label.
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A *Namespace* must exist prior to associating content with it.
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A *Namespace* must not be deleted if there is content associated with it.
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To associate a resource with a *Namespace* the following conditions must be satisfied:
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1. The resource's *Kind* must be registered as having *RESTScopeNamespace* with the server
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2. The resource's *TypeMeta.Namespace* field must have a value that references an existing *Namespace*
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The *Name* of a resource associated with a *Namespace* is unique to that *Kind* in that *Namespace*.
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It is intended to be used in resource URLs; provided by clients at creation time, and encouraged to be
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human friendly; intended to facilitate idempotent creation, space-uniqueness of singleton objects,
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distinguish distinct entities, and reference particular entities across operations.
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### Authorization
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A *Namespace* provides an authorization scope for accessing content associated with the *Namespace*.
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See [Authorization plugins](../admin/authorization.md)
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### Limit Resource Consumption
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A *Namespace* provides a scope to limit resource consumption.
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A *LimitRange* defines min/max constraints on the amount of resources a single entity can consume in
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a *Namespace*.
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See [Admission control: Limit Range](admission_control_limit_range.md)
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A *ResourceQuota* tracks aggregate usage of resources in the *Namespace* and allows cluster operators
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to define *Hard* resource usage limits that a *Namespace* may consume.
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See [Admission control: Resource Quota](admission_control_resource_quota.md)
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### Finalizers
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Upon creation of a *Namespace*, the creator may provide a list of *Finalizer* objects.
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```go
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type FinalizerName string
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// These are internal finalizers to Kubernetes, must be qualified name unless defined here
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const (
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FinalizerKubernetes FinalizerName = "kubernetes"
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)
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// NamespaceSpec describes the attributes on a Namespace
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type NamespaceSpec struct {
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// Finalizers is an opaque list of values that must be empty to permanently remove object from storage
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Finalizers []FinalizerName
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}
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```
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A *FinalizerName* is a qualified name.
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The API Server enforces that a *Namespace* can only be deleted from storage if and only if
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it's *Namespace.Spec.Finalizers* is empty.
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A *finalize* operation is the only mechanism to modify the *Namespace.Spec.Finalizers* field post creation.
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Each *Namespace* created has *kubernetes* as an item in its list of initial *Namespace.Spec.Finalizers*
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set by default.
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### Phases
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A *Namespace* may exist in the following phases.
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```go
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type NamespacePhase string
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const(
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NamespaceActive NamespacePhase = "Active"
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NamespaceTerminating NamespaceTerminating = "Terminating"
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)
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type NamespaceStatus struct {
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...
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Phase NamespacePhase
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}
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```
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A *Namespace* is in the **Active** phase if it does not have a *ObjectMeta.DeletionTimestamp*.
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A *Namespace* is in the **Terminating** phase if it has a *ObjectMeta.DeletionTimestamp*.
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**Active**
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Upon creation, a *Namespace* goes in the *Active* phase. This means that content may be associated with
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a namespace, and all normal interactions with the namespace are allowed to occur in the cluster.
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If a DELETE request occurs for a *Namespace*, the *Namespace.ObjectMeta.DeletionTimestamp* is set
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to the current server time. A *namespace controller* observes the change, and sets the *Namespace.Status.Phase*
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to *Terminating*.
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**Terminating**
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A *namespace controller* watches for *Namespace* objects that have a *Namespace.ObjectMeta.DeletionTimestamp*
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value set in order to know when to initiate graceful termination of the *Namespace* associated content that
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are known to the cluster.
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The *namespace controller* enumerates each known resource type in that namespace and deletes it one by one.
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Admission control blocks creation of new resources in that namespace in order to prevent a race-condition
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where the controller could believe all of a given resource type had been deleted from the namespace,
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when in fact some other rogue client agent had created new objects. Using admission control in this
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scenario allows each of registry implementations for the individual objects to not need to take into account Namespace life-cycle.
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Once all objects known to the *namespace controller* have been deleted, the *namespace controller*
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executes a *finalize* operation on the namespace that removes the *kubernetes* value from
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the *Namespace.Spec.Finalizers* list.
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If the *namespace controller* sees a *Namespace* whose *ObjectMeta.DeletionTimestamp* is set, and
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whose *Namespace.Spec.Finalizers* list is empty, it will signal the server to permanently remove
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the *Namespace* from storage by sending a final DELETE action to the API server.
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### REST API
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To interact with the Namespace API:
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| Action | HTTP Verb | Path | Description |
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| ------ | --------- | ---- | ----------- |
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| CREATE | POST | /api/{version}/namespaces | Create a namespace |
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| LIST | GET | /api/{version}/namespaces | List all namespaces |
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| UPDATE | PUT | /api/{version}/namespaces/{namespace} | Update namespace {namespace} |
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| DELETE | DELETE | /api/{version}/namespaces/{namespace} | Delete namespace {namespace} |
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| FINALIZE | POST | /api/{version}/namespaces/{namespace}/finalize | Finalize namespace {namespace} |
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| WATCH | GET | /api/{version}/watch/namespaces | Watch all namespaces |
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This specification reserves the name *finalize* as a sub-resource to namespace.
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As a consequence, it is invalid to have a *resourceType* managed by a namespace whose kind is *finalize*.
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To interact with content associated with a Namespace:
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| Action | HTTP Verb | Path | Description |
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| ---- | ---- | ---- | ---- |
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| CREATE | POST | /api/{version}/namespaces/{namespace}/{resourceType}/ | Create instance of {resourceType} in namespace {namespace} |
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| GET | GET | /api/{version}/namespaces/{namespace}/{resourceType}/{name} | Get instance of {resourceType} in namespace {namespace} with {name} |
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| UPDATE | PUT | /api/{version}/namespaces/{namespace}/{resourceType}/{name} | Update instance of {resourceType} in namespace {namespace} with {name} |
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| DELETE | DELETE | /api/{version}/namespaces/{namespace}/{resourceType}/{name} | Delete instance of {resourceType} in namespace {namespace} with {name} |
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| LIST | GET | /api/{version}/namespaces/{namespace}/{resourceType} | List instances of {resourceType} in namespace {namespace} |
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| WATCH | GET | /api/{version}/watch/namespaces/{namespace}/{resourceType} | Watch for changes to a {resourceType} in namespace {namespace} |
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| WATCH | GET | /api/{version}/watch/{resourceType} | Watch for changes to a {resourceType} across all namespaces |
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| LIST | GET | /api/{version}/list/{resourceType} | List instances of {resourceType} across all namespaces |
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The API server verifies the *Namespace* on resource creation matches the *{namespace}* on the path.
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The API server will associate a resource with a *Namespace* if not populated by the end-user based on the *Namespace* context
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of the incoming request. If the *Namespace* of the resource being created, or updated does not match the *Namespace* on the request,
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then the API server will reject the request.
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### Storage
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A namespace provides a unique identifier space and therefore must be in the storage path of a resource.
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In etcd, we want to continue to still support efficient WATCH across namespaces.
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Resources that persist content in etcd will have storage paths as follows:
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/{k8s_storage_prefix}/{resourceType}/{resource.Namespace}/{resource.Name}
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This enables consumers to WATCH /registry/{resourceType} for changes across namespace of a particular {resourceType}.
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### Kubelet
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The kubelet will register pod's it sources from a file or http source with a namespace associated with the
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*cluster-id*
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### Example: OpenShift Origin managing a Kubernetes Namespace
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In this example, we demonstrate how the design allows for agents built on-top of
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Kubernetes that manage their own set of resource types associated with a *Namespace*
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to take part in Namespace termination.
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OpenShift creates a Namespace in Kubernetes
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```json
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{
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"apiVersion":"v1",
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"kind": "Namespace",
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"metadata": {
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"name": "development",
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"labels": {
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"name": "development"
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}
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},
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"spec": {
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"finalizers": ["openshift.com/origin", "kubernetes"]
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},
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"status": {
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"phase": "Active"
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}
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}
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```
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OpenShift then goes and creates a set of resources (pods, services, etc) associated
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with the "development" namespace. It also creates its own set of resources in its
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own storage associated with the "development" namespace unknown to Kubernetes.
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User deletes the Namespace in Kubernetes, and Namespace now has following state:
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```json
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{
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"apiVersion":"v1",
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"kind": "Namespace",
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"metadata": {
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"name": "development",
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"deletionTimestamp": "..."
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"labels": {
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"name": "development"
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}
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},
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"spec": {
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"finalizers": ["openshift.com/origin", "kubernetes"]
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},
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"status": {
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"phase": "Terminating"
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}
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}
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```
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The Kubernetes *namespace controller* observes the namespace has a *deletionTimestamp*
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and begins to terminate all of the content in the namespace that it knows about. Upon
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success, it executes a *finalize* action that modifies the *Namespace* by
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removing *kubernetes* from the list of finalizers:
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```json
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{
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"apiVersion":"v1",
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"kind": "Namespace",
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"metadata": {
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"name": "development",
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"deletionTimestamp": "..."
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"labels": {
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"name": "development"
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}
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},
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"spec": {
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"finalizers": ["openshift.com/origin"]
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},
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"status": {
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"phase": "Terminating"
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}
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}
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```
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OpenShift Origin has its own *namespace controller* that is observing cluster state, and
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it observes the same namespace had a *deletionTimestamp* assigned to it. It too will go
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and purge resources from its own storage that it manages associated with that namespace.
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Upon completion, it executes a *finalize* action and removes the reference to "openshift.com/origin"
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from the list of finalizers.
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This results in the following state:
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```json
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{
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"apiVersion":"v1",
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"kind": "Namespace",
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"metadata": {
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"name": "development",
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"deletionTimestamp": "..."
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"labels": {
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"name": "development"
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}
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},
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"spec": {
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"finalizers": []
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},
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"status": {
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"phase": "Terminating"
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}
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}
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```
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At this point, the Kubernetes *namespace controller* in its sync loop will see that the namespace
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has a deletion timestamp and that its list of finalizers is empty. As a result, it knows all
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content associated from that namespace has been purged. It performs a final DELETE action
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to remove that Namespace from the storage.
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At this point, all content associated with that Namespace, and the Namespace itself are gone.
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[]()
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<!-- END MUNGE: GENERATED_ANALYTICS -->
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