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