- janetkuo title: Sharing a Cluster with Namespaces
A Namespace is a mechanism to partition resources created by users into a logically named group.
A single cluster should be able to satisfy the needs of multiple users or groups of users (henceforth a 'user community').
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
- 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.
You can list the current namespaces in a cluster using:
$ kubectl get namespaces NAME STATUS AGE default Active 11d kube-system Active 11d
Kubernetes starts with two initial namespaces:
defaultThe default namespace for objects with no other namespace
kube-systemThe namespace for objects created by the Kubernetes system
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> 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
To create a new namespace, first create a new YAML file called
my-namespace.yaml with the contents:
apiVersion: v1 kind: Namespace metadata: name: <insert-namespace-name-here>
$ kubectl create -f ./my-namespace.yaml
Note that the name of your namespace must be a DNS compatible 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.
Working in namespaces
Deleting a namespace
You can 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
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).