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Share a Cluster with Namespaces

This page shows how to view, work in, and delete namespacesAn abstraction used by Kubernetes to support multiple virtual clusters on the same physical cluster. . The page also shows how to use Kubernetes namespaces to subdivide your cluster.

Before you begin

Viewing namespaces

  1. List the current namespaces in a cluster using:

    kubectl get namespaces
    NAME          STATUS    AGE
default       Active    11d
kube-system   Active    11d
kube-public   Active    11d

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.

You can also get the summary of a specific namespace using:

kubectl get namespaces <name>

Or you can get detailed information with:

kubectl describe namespaces <name>
Name:           default
Labels:         <none>
Annotations:    <none>
Status:         Active

No resource quota.

Resource Limits
 Type       Resource    Min Max Default
 ----               --------    --- --- ---
 Container          cpu         -   -   100m

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.

A limit range defines min/max constraints on the amount of resources a single entity can consume in a Namespace.

See Admission control: Limit Range

A namespace can be in one of two phases:

  • Active the namespace is in use
  • Terminating the namespace is being deleted, and can not be used for new objects

See the design doc for more details.

Creating a new namespace

  1. Create a new YAML file called my-namespace.yaml with the contents:

    apiVersion: v1
kind: Namespace
metadata:
  name: <insert-namespace-name-here>

    Then run:

    kubectl create -f ./my-namespace.yaml

  2. Alternatively, you can create namespace using below command:

    kubectl create namespace <insert-namespace-name-here>

The name of your namespace must be a valid DNS label.

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.

Deleting a namespace

Delete a namespace with

kubectl delete namespaces <insert-some-namespace-name>
Warning: This deletes everything under the namespace!

This delete is asynchronous, so for a time you will see the namespace in the Terminating state.

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.

    Assuming you have a fresh cluster, you can introspect the available namespaces by doing the following:

    kubectl get namespaces
    NAME      STATUS    AGE
default   Active    13m

  2. 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:

    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.

    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:

    kubectl create -f https://k8s.io/examples/admin/namespace-dev.json

    And then let’s create the production namespace using kubectl:

    kubectl create -f https://k8s.io/examples/admin/namespace-prod.json

    To be sure things are right, list all of the namespaces in our cluster.

    kubectl get namespaces --show-labels
    NAME          STATUS    AGE       LABELS
default       Active    32m       <none>
development   Active    29s       name=development
production    Active    23s       name=production

  3. 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.

    kubectl run snowflake --image=k8s.gcr.io/serve_hostname --replicas=2 -n=development

    We have just created a deployment whose replica size is 2 that is running the pod called snowflake with a basic container that just serves the hostname. Note that kubectl run creates deployments only on Kubernetes cluster >= v1.2. If you are running older versions, it creates replication controllers instead. If you want to obtain the old behavior, use --generator=run/v1 to create replication controllers. See kubectl run for more details.

    kubectl get deployment -n=development
    NAME         READY   UP-TO-DATE   AVAILABLE   AGE
snowflake    2/2     2            2           2m

    kubectl get pods -l run=snowflake -n=development
    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.

    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.

    kubectl get deployment -n=production
kubectl get pods -n=production

    Production likes to run cattle, so let’s create some cattle pods.

    kubectl run cattle --image=k8s.gcr.io/serve_hostname --replicas=5 -n=production

kubectl get deployment -n=production
    NAME         READY   UP-TO-DATE   AVAILABLE   AGE
cattle       5/5     5            5           10s

    kubectl get pods -l run=cattle -n=production
    NAME                      READY     STATUS    RESTARTS   AGE
cattle-2263376956-41xy6   1/1       Running   0          34s
cattle-2263376956-kw466   1/1       Running   0          34s
cattle-2263376956-n4v97   1/1       Running   0          34s
cattle-2263376956-p5p3i   1/1       Running   0          34s
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.

As the policy support in Kubernetes evolves, we will extend this scenario to show how you can provide different authorization rules for each namespace.

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’).

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.
  2. 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.)

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

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 isolation of what other user communities are doing on the cluster.

Understanding namespaces and DNS

When you create a Service, it creates a corresponding DNS entry. This entry is of the form <service-name>.<namespace-name>.svc.cluster.local, which means that if a container just 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).

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