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Merge pull request #41256 from tengqm/tweak-namespaces 

Reformat paragraphs in the namespaces task page
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content/en/docs/tasks/administer-cluster/namespaces.md
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@ -8,25 +8,26 @@ weight: 340
---
<!-- overview -->
This page shows how to view, work in, and delete {{< glossary_tooltip text="namespaces" term_id="namespace" >}}. The page also shows how to use Kubernetes namespaces to subdivide your cluster.
This page shows how to view, work in, and delete {{< glossary_tooltip text="namespaces" term_id="namespace" >}}.
The page also shows how to use Kubernetes namespaces to subdivide your cluster.
## {{% heading "prerequisites" %}}
* Have an [existing Kubernetes cluster](/docs/setup/).
* You have a basic understanding of Kubernetes {{< glossary_tooltip text="Pods" term_id="pod" >}}, {{< glossary_tooltip term_id="service" text="Services" >}}, and {{< glossary_tooltip text="Deployments" term_id="deployment" >}}.
* You have a basic understanding of Kubernetes {{< glossary_tooltip text="Pods" term_id="pod" >}},
{{< glossary_tooltip term_id="service" text="Services" >}}, and
{{< glossary_tooltip text="Deployments" term_id="deployment" >}}.
<!-- steps -->
## Viewing namespaces
1. List the current namespaces in a cluster using:
List the current namespaces in a cluster using:
```shell
kubectl get namespaces
```
```
```console
NAME STATUS AGE
default Active 11d
kube-system Active 11d
@ -37,7 +38,10 @@ Kubernetes starts with three initial namespaces:
* `default` The default namespace for objects with no other namespace
* `kube-system` The namespace for objects created by the Kubernetes system
* `kube-public` This namespace is created automatically and is readable by all users (including those not authenticated). This namespace is mostly reserved for cluster usage, in case that some resources should be visible and readable publicly throughout the whole cluster. The public aspect of this namespace is only a convention, not a requirement.
* `kube-public` This namespace is created automatically and is readable by all users
(including those not authenticated). This namespace is mostly reserved for cluster usage,
in case that some resources should be visible and readable publicly throughout the whole cluster.
The public aspect of this namespace is only a convention, not a requirement.
You can also get the summary of a specific namespace using:
@ -50,7 +54,7 @@ Or you can get detailed information with:
```shell
kubectl describe namespaces <name>
```
```
```console
Name: default
Labels: <none>
Annotations: <none>
@ -66,11 +70,11 @@ Resource Limits
Note that these details show both resource quota (if present) as well as resource limit ranges.
Resource quota tracks aggregate usage of resources in the *Namespace* and allows cluster operators
to define *Hard* resource usage limits that a *Namespace* may consume.
Resource quota tracks aggregate usage of resources in the Namespace and allows cluster operators
to define *Hard* resource usage limits that a Namespace may consume.
A limit range defines min/max constraints on the amount of resources a single entity can consume in
a *Namespace*.
a Namespace.
See [Admission control: Limit Range](https://git.k8s.io/design-proposals-archive/resource-management/admission_control_limit_range.md)
@ -88,7 +92,7 @@ in the API reference.
Avoid creating namespace with prefix `kube-`, since it is reserved for Kubernetes system namespaces.
{{< /note >}}
1. Create a new YAML file called `my-namespace.yaml` with the contents:
Create a new YAML file called `my-namespace.yaml` with the contents:
```yaml
apiVersion: v1
@ -98,22 +102,25 @@ in the API reference.
```
Then run:
```
```shell
kubectl create -f ./my-namespace.yaml
```
2. Alternatively, you can create namespace using below command:
Alternatively, you can create namespace using below command:
```
```shell
kubectl create namespace <insert-namespace-name-here>
```
The name of your namespace must be a valid
[DNS label](/docs/concepts/overview/working-with-objects/names#dns-label-names).
There's an optional field `finalizers`, which allows observables to purge resources whenever the namespace is deleted. Keep in mind that if you specify a nonexistent finalizer, the namespace will be created but will get stuck in the `Terminating` state if the user tries to delete it.
There's an optional field `finalizers`, which allows observables to purge resources whenever the
namespace is deleted. Keep in mind that if you specify a nonexistent finalizer, the namespace will
be created but will get stuck in the `Terminating` state if the user tries to delete it.
More information on `finalizers` can be found in the namespace [design doc](https://git.k8s.io/design-proposals-archive/architecture/namespaces.md#finalizers).
More information on `finalizers` can be found in the namespace
[design doc](https://git.k8s.io/design-proposals-archive/architecture/namespaces.md#finalizers).
## Deleting a namespace
@ -131,37 +138,37 @@ This delete is asynchronous, so for a time you will see the namespace in the `Te
## Subdividing your cluster using Kubernetes namespaces
1. Understand the default namespace
By default, a Kubernetes cluster will instantiate a default namespace when provisioning the cluster to hold the default set of Pods,
Services, and Deployments used by the cluster.
By default, a Kubernetes cluster will instantiate a default namespace when provisioning the
cluster to hold the default set of Pods, Services, and Deployments used by the cluster.
Assuming you have a fresh cluster, you can introspect the available namespaces by doing the following:
```shell
kubectl get namespaces
```
```
```console
NAME STATUS AGE
default Active 13m
```
2. Create new namespaces
### Create new namespaces
For this exercise, we will create two additional Kubernetes namespaces to hold our content.
In a scenario where an organization is using a shared Kubernetes cluster for development and production use cases:
In a scenario where an organization is using a shared Kubernetes cluster for development and
production use cases:
The development team would like to maintain a space in the cluster where they can get a view on the list of Pods, Services, and Deployments
they use to build and run their application. In this space, Kubernetes resources come and go, and the restrictions on who can or cannot modify resources
are relaxed to enable agile development.
- The development team would like to maintain a space in the cluster where they can get a view on
the list of Pods, Services, and Deployments they use to build and run their application.
In this space, Kubernetes resources come and go, and the restrictions on who can or cannot modify
resources are relaxed to enable agile development.
The operations team would like to maintain a space in the cluster where they can enforce strict procedures on who can or cannot manipulate the set of
Pods, Services, and Deployments that run the production site.
- The operations team would like to maintain a space in the cluster where they can enforce strict
procedures on who can or cannot manipulate the set of Pods, Services, and Deployments that run
the production site.
One pattern this organization could follow is to partition the Kubernetes cluster into two namespaces: `development` and `production`.
Let's create two new namespaces to hold our work.
One pattern this organization could follow is to partition the Kubernetes cluster into two
namespaces: `development` and `production`. Let's create two new namespaces to hold our work.
Create the `development` namespace using kubectl:
@ -180,47 +187,51 @@ This delete is asynchronous, so for a time you will see the namespace in the `Te
```shell
kubectl get namespaces --show-labels
```
```
```console
NAME STATUS AGE LABELS
default Active 32m <none>
development Active 29s name=development
production Active 23s name=production
```
3. Create pods in each namespace
### Create pods in each namespace
A Kubernetes namespace provides the scope for Pods, Services, and Deployments in the cluster.
Users interacting with one namespace do not see the content in another namespace.
To demonstrate this, let's spin up a simple Deployment and Pods in the `development` namespace.
```shell
kubectl create deployment snowflake --image=registry.k8s.io/serve_hostname -n=development --replicas=2
kubectl create deployment snowflake \
--image=registry.k8s.io/serve_hostname \
-n=development --replicas=2
```
We have created a deployment whose replica size is 2 that is running the pod called `snowflake` with a basic container that serves the hostname.
We have created a deployment whose replica size is 2 that is running the pod called `snowflake`
with a basic container that serves the hostname.
```shell
kubectl get deployment -n=development
```
```
```console
NAME READY UP-TO-DATE AVAILABLE AGE
snowflake 2/2 2 2 2m
```
```shell
kubectl get pods -l app=snowflake -n=development
```
```
```console
NAME READY STATUS RESTARTS AGE
snowflake-3968820950-9dgr8 1/1 Running 0 2m
snowflake-3968820950-vgc4n 1/1 Running 0 2m
```
And this is great, developers are able to do what they want, and they do not have to worry about affecting content in the `production` namespace.
And this is great, developers are able to do what they want, and they do not have to worry about
affecting content in the `production` namespace.
Let's switch to the `production` namespace and show how resources in one namespace are hidden from the other.
The `production` namespace should be empty, and the following commands should return nothing.
Let's switch to the `production` namespace and show how resources in one namespace are hidden from
the other. The `production` namespace should be empty, and the following commands should return nothing.
```shell
kubectl get deployment -n=production
@ -235,7 +246,8 @@ This delete is asynchronous, so for a time you will see the namespace in the `Te
kubectl get deployment -n=production
```
```
```console
NAME READY UP-TO-DATE AVAILABLE AGE
cattle 5/5 5 5 10s
```
@ -243,7 +255,7 @@ This delete is asynchronous, so for a time you will see the namespace in the `Te
```shell
kubectl get pods -l app=cattle -n=production
```
```
```console
NAME READY STATUS RESTARTS AGE
cattle-2263376956-41xy6 1/1 Running 0 34s
cattle-2263376956-kw466 1/1 Running 0 34s
@ -252,70 +264,66 @@ This delete is asynchronous, so for a time you will see the namespace in the `Te
cattle-2263376956-sxpth 1/1 Running 0 34s
```
At this point, it should be clear that the resources users create in one namespace are hidden from the other namespace.
At this point, it should be clear that the resources users create in one namespace are hidden from
the other namespace.
As the policy support in Kubernetes evolves, we will extend this scenario to show how you can provide different
authorization rules for each namespace.
<!-- discussion -->
## Understanding the motivation for using namespaces
A single cluster should be able to satisfy the needs of multiple users or groups of users (henceforth a 'user community').
A single cluster should be able to satisfy the needs of multiple users or groups of users
(henceforth in this document a _user community_).
Kubernetes _namespaces_ help different projects, teams, or customers to share a Kubernetes cluster.
It does this by providing the following:
1. A scope for [Names](/docs/concepts/overview/working-with-objects/names/).
2. A mechanism to attach authorization and policy to a subsection of the cluster.
1. A scope for [names](/docs/concepts/overview/working-with-objects/names/).
1. A mechanism to attach authorization and policy to a subsection of the cluster.
Use of multiple namespaces is optional.
Each user community wants to be able to work in isolation from other communities.
Each user community has its own:
1. resources (pods, services, replication controllers, etc.)
2. policies (who can or cannot perform actions in their community)
3. constraints (this community is allowed this much quota, etc.)
1. policies (who can or cannot perform actions in their community)
1. constraints (this community is allowed this much quota, etc.)
A cluster operator may create a Namespace for each unique user community.
The Namespace provides a unique scope for:
1. named resources (to avoid basic naming collisions)
2. delegated management authority to trusted users
3. ability to limit community resource consumption
1. delegated management authority to trusted users
1. ability to limit community resource consumption
Use cases include:
1. As a cluster operator, I want to support multiple user communities on a single cluster.
2. As a cluster operator, I want to delegate authority to partitions of the cluster to trusted users
in those communities.
3. As a cluster operator, I want to limit the amount of resources each community can consume in order
to limit the impact to other communities using the cluster.
4. As a cluster user, I want to interact with resources that are pertinent to my user community in
1. As a cluster operator, I want to delegate authority to partitions of the cluster to trusted
users in those communities.
1. As a cluster operator, I want to limit the amount of resources each community can consume in
order to limit the impact to other communities using the cluster.
1. As a cluster user, I want to interact with resources that are pertinent to my user community in
isolation of what other user communities are doing on the cluster.
## Understanding namespaces and DNS
When you create a [Service](/docs/concepts/services-networking/service/), it creates a corresponding [DNS entry](/docs/concepts/services-networking/dns-pod-service/).
When you create a [Service](/docs/concepts/services-networking/service/), it creates a corresponding
[DNS entry](/docs/concepts/services-networking/dns-pod-service/).
This entry is of the form `<service-name>.<namespace-name>.svc.cluster.local`, which means
that if a container uses `<service-name>` it will resolve to the service which
is local to a namespace. This is useful for using the same configuration across
multiple namespaces such as Development, Staging and Production. If you want to reach
across namespaces, you need to use the fully qualified domain name (FQDN).
## {{% heading "whatsnext" %}}
* Learn more about [setting the namespace preference](/docs/concepts/overview/working-with-objects/namespaces/#setting-the-namespace-preference).
* Learn more about [setting the namespace for a request](/docs/concepts/overview/working-with-objects/namespaces/#setting-the-namespace-for-a-request)
* See [namespaces design](https://git.k8s.io/design-proposals-archive/architecture/namespaces.md).