90 lines
3.2 KiB
Markdown
90 lines
3.2 KiB
Markdown
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---
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---
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Kubernetes supports multiple virtual clusters backed by the same physical cluster.
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These virtual clusters are called namespaces.
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## When to Use Multiple Namespaces
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Namespaces are intended for use in environments with many users spread across multiple
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teams, or projects. For clusters with a few to tens of users, you should not
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need to create or think about namespaces at all. Start using namespaces when you
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need the features they provide.
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Namespaces provide a scope for names. Names of resources need to be unique within a namespace, but not across namespaces.
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Namespaces are a way to divide cluster resources between multiple uses (via [resource quota](/docs/admin/resource-quota)).
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In future versions of Kubernetes, objects in the same namespace will have the same
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access control policies by default.
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It is not necessary to use multiple namespaces just to separate slightly different
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resources, such as different versions of the same software: use [labels](/docs/user-guide/labels) to distinguish
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resources within the same namespace.
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## Working with Namespaces
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Creation and deletion of namespaces is described in the [Admin Guide documentation
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for namespaces](/docs/admin/namespaces)
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### Viewing namespaces
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You can list the current namespaces in a cluster using:
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```shell
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$ kubectl get namespaces
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NAME LABELS STATUS
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default <none> Active
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kube-system <none> Active
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```
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Kubernetes starts with two initial namespaces:
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* `default` The default namespace for objects with no other namespace
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* `kube-system` The namespace for objects created by the Kubernetes system
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### Setting the namespace for a request
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To temporarily set the namespace for a request, use the `--namespace` flag.
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For example:
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```shell
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$ kubectl --namespace=<insert-namespace-name-here> run nginx --image=nginx
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$ kubectl --namespace=<insert-namespace-name-here> get pods
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```
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### Setting the namespace preference
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You can permanently save the namespace for all subsequent kubectl commands in that
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context.
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First get your current context:
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```shell
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$ export CONTEXT=$(kubectl config view | grep current-context | awk '{print $2}')
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```
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Then update the default namespace:
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```shell
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$ kubectl config set-context $(CONTEXT) --namespace=<insert-namespace-name-here>
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```
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## Namespaces and DNS
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When you create a [Service](/docs/user-guide/services), it creates a corresponding [DNS entry](/docs/admin/dns).
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This entry is of the form `<service-name>.<namespace-name>.svc.cluster.local`, which means
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that if a container just uses `<service-name>` it will resolve to the service which
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is local to a namespace. This is useful for using the same configuration across
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multiple namespaces such as Development, Staging and Production. If you want to reach
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across namespaces, you need to use the fully qualified domain name (FQDN).
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## Not All Objects are in a Namespace
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Most kubernetes resources (e.g. pods, services, replication controllers, and others) are
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in a some namespace. However namespace resources are not themselves in a namespace.
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And, low-level resources, such as [nodes](/docs/admin/node) and
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persistentVolumes, are not in any namespace. Events are an exception: they may or may not
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have a namespace, depending on the object the event is about.
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