Namespaces

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 cannot be nested inside one another and each Kubernetes resource can only be in one namespace.

Namespaces are a way to divide cluster resources between multiple users (via resource quota).

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 are described in the Admin Guide documentation for namespaces.

Note: Avoid creating namespace with prefix kube-, since it is reserved for Kubernetes system namespaces.

Viewing namespaces

You can list the current namespaces in a cluster using:

  1. kubectl get namespace
  1. NAME              STATUS   AGE
  2. default           Active   1d
  3. kube-node-lease   Active   1d
  4. kube-public       Active   1d
  5. kube-system       Active   1d

Kubernetes starts with four 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.
  • kube-node-lease This namespace for the lease objects associated with each node which improves the performance of the node heartbeats as the cluster scales.

Setting the namespace for a request

To set the namespace for a current request, use the --namespace flag.

For example:

  1. kubectl run nginx --image=nginx --namespace=<insert-namespace-name-here>
  2. kubectl get pods --namespace=<insert-namespace-name-here>

Setting the namespace preference

You can permanently save the namespace for all subsequent kubectl commands in that context.

  1. kubectl config set-context --current --namespace=<insert-namespace-name-here>
  2. # Validate it
  3. kubectl config view --minify | 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 namespaces. However namespace resources are not themselves in a namespace. And low-level resources, such as nodes and persistentVolumes, are not in any namespace.

To see which Kubernetes resources are and aren’t in a namespace:

  1. # In a namespace
  2. kubectl api-resources --namespaced=true
  4. # Not in a namespace
  5. kubectl api-resources --namespaced=false

What’s next