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
- Have an existing Kubernetes cluster.
- You have a basic understanding of Kubernetes PodsA Pod represents a set of running containers in your cluster. , ServicesA way to expose an application running on a set of Pods as a network service. , and DeploymentsManages a replicated application on your cluster. .
- 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:
defaultThe default namespace for objects with no other namespace
kube-systemThe namespace for objects created by the Kubernetes system
kube-publicThis 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.
A namespace can be in one of two phases:
Activethe namespace is in use
Terminatingthe namespace is being deleted, and can not be used for new objects
See the design doc for more details.
Creating a new namespace
Note: Avoid creating namespace with prefix
kube-, since it is reserved for Kubernetes system namespaces.
Create a new YAML file called
my-namespace.yamlwith the contents:
apiVersion: v1 kind: Namespace metadata: name: <insert-namespace-name-here>
kubectl create -f ./my-namespace.yaml
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
Subdividing your cluster using Kubernetes namespaces
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
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:
Let's create two new namespaces to hold our work.
developmentnamespace using kubectl:
kubectl create -f https://k8s.io/examples/admin/namespace-dev.json
And then let's create the
productionnamespace 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
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
kubectl create deployment snowflake --image=k8s.gcr.io/serve_hostname -n=development kubectl scale deployment snowflake --replicas=2 -n=development
We have just created a deployment whose replica size is 2 that is running the pod called
snowflakewith a basic container that just serves the hostname.
kubectl get deployment -n=development
NAME READY UP-TO-DATE AVAILABLE AGE snowflake 2/2 2 2 2m
kubectl get pods -l app=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
Let's switch to the
productionnamespace and show how resources in one namespace are hidden from the other.
productionnamespace 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 create deployment cattle --image=k8s.gcr.io/serve_hostname -n=production kubectl scale deployment cattle --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 app=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:
- A scope for Names.
- 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:
- resources (pods, services, replication controllers, etc.)
- policies (who can or cannot perform actions in their community)
- 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:
- named resources (to avoid basic naming collisions)
- delegated management authority to trusted users
- ability to limit community resource consumption
Use cases include:
- As a cluster operator, I want to support multiple user communities on a single cluster.
- As a cluster operator, I want to delegate authority to partitions of the cluster to trusted users in those communities.
- 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.
- 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).