What is a Kubernetes Namespace?

Small teams or smaller organizations may be perfectly content using the default namespace. This is particularly relevant if there is no need to isolate developers or users from each other. However, there are many useful benefits to having multiple namespaces, including:

• Isolation. Large or growing teams can use namespaces to isolate their projects and microservices from each other. Teams can re-use the same resource names in different workspaces without a problem. Also, taking an action on items in one workspace never affects other workspaces.
• Organization. Organizations that use a single cluster for development, testing, and production can use namespaces to sandbox dev and test environments. This ensures production code is not affected by changes that developers or testers make in their own namespaces throughout the application lifecycle.
• Permissions. Namespaces enable the use of Kubernetes RBAC, so teams can define roles that group lists of permissions or abilities under a single name. This can ensure that only authorized users have access to resources in a given namespace. 
• Resource Control. Policy-driven resource limits can be set on namespaces by defining resource quotas for CPU or memory utilization. This can ensure that every project or namespace has the resources it needs to run, and that no one namespace is hogging all available resources.
• Performance. Using namespaces can help improve performance of a given cluster. If a cluster is separated into multiple namespaces for different projects, the Kubernetes API will have fewer items to search when performing operations. This can reduce latency and speed overall application performance for each application running on the cluster.

How can pods communicate across Kubernetes namespaces?

Although namespaces are separate from each other, they can easily communicate with each other. Kubernetes DNS service directory can easily locate any service by its name by using the expanded form of DNS addressing:

..svc.cluster.local

Simply adding the namespace name to the service name provides access to services in any namespace on the cluster. For example, to access the payroll service in the development namespace you would use the address
payroll.development
To access the payroll service in the production namespace you would use:
payroll.production

Note that network policies can optionally be utilized to control access between namespaces. For example, a network policy can allow or deny all traffic from other namespaces. Network polices apply only to connections and are not a substitute for firewalls that perform packet inspection.

What is the command to find current Kubernetes namespaces?

All namespaces in the cluster can be displayed with the command:
kubectl get namespace
This will return a list of all namespaces in the cluster, including the default namespaces, along with their status and age.

What is the command to create a new Kubernetes namespace?

Namespaces are created simply with the command:
kubectl create namespace
As with any other Kubernetes resource, a YAML file can also be created and applied to create a namespace:

newspace.yaml:
kind: Namespace
apiVersion: v1
metadata:
name: newspace
labels:
name: newspacekubectl apply -f newspace.yaml

How do you switch between Kubernetes namespaces?

To address namespaces once they are created, actions must include the –namepsace= option in the command. Since this can get cumbersome, the default namespace can be changed by using the kubectl config command to set the namespace in the cluster context.
For example, to change from the default namespace to one named ‘testing’ you would enter:
kubectl config set-context --current --namespace=testing
This will set the default namespace to ‘testing’ for all future kubectl commands.

How do you rename a Kubernetes namespace?

It is not standard practice to rename a Kubernetes namespace, so choose namespaces (outside of the default) carefully.

How do you delete a Kubernetes namespace?

Namespaces are deleted with the command:
kubectl delete namespaces
Since the deletion is an asynchronous activity, the namespace will show as ‘terminating’ until the namespace is deleted.

A warning about deleting Kubernetes namespaces

Deleting a namespace is a final act. Everything in the namespace including all services, running pods, and artifacts will be deleted. Garbage collection will run on anything that had existed in that namespace. Be certain everything in the namespace should be deleted before taking this action.