On the first post we saw how to deploy a Kubernetes platform using Vagrant and VirtualBox. Now we want to see how the cluster resources are logically segregated using Kubernetes namespaces. A namespace gives you the way to enable multi-tenancy in Kubernetes, RBAC, and have an isolated space where you won’t have any naming conflict with other namespaces.
Getting started with namespaces
The following sections will walk you through the procedure to understand when you must use namespaces. In addition you will learn how to create and operate them.
As an illustration let’s presume you are providing Container as a Service (a.k.a. CaaS) to your organisation, customers, or yourself. As shown above on the diagram the common use cases for namespaces are:
- Multi-tenancy. You want to isolate organisations or customer on a shared Kubernetes platform. Kubernetes namespaces cannot be nested. If you have the namespace CustomerA and later on it requires two new namespaces for development and production, you cannot create sub-namespaces under the CustomerA namespace. It will require to create two namespaces like CustomerA-dev and CustomerA-prod.
- Environment. If you desire to keep separated your development of production, you can create two namespaces one called Dev and the other Prod.
- Project. Keep your projects on dedicated namespaces. It helps with CI/CD as well as a better utilisation and tracking of resources.
- Team. If you are on a DevOps environment, the partitioning based on project or team is the same. On the contrary, you can create a playground area for learning purpose.
If you want more information about use cases take a look to this post.
The following approach is just a suggestion to have unique and scalable namespaces. Uses hyphens to separate the groups.
- Customer/Organisation code. At least a minimum of three letters
- Environment code. At least a minimum of three letters
- Project/Service code. At least a minimum of three letters
- Digits. At least a minimum of two numbers
Remember to use lowercase for your namespace name. This is an example using the convention above: jlg-prod-blog-01.
Operating with namespaces
Before we crack on with the creation of namespaces let’s take a look to the Kubernetes command-line tool called kubectl.
Kubectl is the command-line to operate Kubernetes clusters and its applications. It’s available for the majority of the operating systems. If you have deployed your Kubernetes platform using the Vagrantfile I have created, the master node has kubectl installed and configured for you.
If you want to know more about kubectl, please visit this link.
To list any kind of Kubernetes object you use kubectl get <object_type>. Our object type is namespace so our command shows as follows:
By default any Kubernetes configuration tool creates at least two namespaces, default and kube-system. In our case we can see three because kube-public is created when you use kubeadm as the Kubernetes configuration tool.
- default. This namespace is used when you don’t specify a different namespace using -n <namespace_name> or –namespace <namespace_name>.
- kube-system. This is the namespace where all the Kubernetes core components are running.
- kube-public (only with kubeadm). This namespace is readable by everyone, including those not authenticated. This namespace is used by kubeadm to host a ConfigMap object in order to enable a secure bootstrap with a simple and short shared token.
You can see the details of an object using kubectl describe <object_type> <object_name>. Our object type is namespace and the object name we will use is kube-system. The command shows as follows:
As you can see the output is pretty simple. This is because we are working with a fresh Kubernetes installation. Also, the most common additional extra settings for a namespace like resource quotas and limits are not defined yet. Those objects will be covered on a future post.
Using the kubectl command you can create objects on two ways.
The first way is to create the object from the CLI without use a manifest file. This approach is supported for a limited number of Kubernetes objects. Let’s create a namespace called no-manifest.
The second way is to use a manifest file. This is the preferred method since it enables the opportunity to track and version your infrastructure as code manifests on your source code repository. Let’s create a namespace called manifest using a YAML file.
As you could see the manifest file for a namespace is simple. Other attributes like labels or annotations can be added on.
You can edit the Kubernetes objects on fly with the command kubectl edit <object_type> <object_name> -n <namespace>. On our next example we don’t need to use -n namespace since we are editing one. For objects self-contained in a namespace, you must specify the namespace for the object. Let’s config the annotations with a description for our namespace called no-manifest.
The deletion of a namespace removes ALL the child objects contained within the namespace. Before you delete a namespace make sure the objects in the namespace are not required anymore. Let’s delete the namespace called manifest with the command kubectl delete namespace manifest.
Real Kubernetes Namespaces example
For the purpose of this real case scenario we are going to create a namespace to group the different kind of web servers. After you have created the namespace, you will proceed with the deployment of Nginx. Finally, you will list all the objects in the created namespace.
Int he first place let’s create a new namespace called webservers.
In addition, we are going to create a deployment so we can see later on how they are contain in a namespace.
As a result let’s list the components in our namespace using the command kubectl get all -n webservers.
On the output above you can see what a deployment creates.
- Deployments (deploy). This controller provides declarative updates for Pods (po) and ReplicaSets (rs). The controller is responsible to ensure the desire state of your application. You can see two deployments with the same ID (dep-nginx), this is because it’s created at cluster level rather than per node. Since we have two Kubernetes nodes it shows the object available for all the nodes in the cluster.
- ReplicaSets (rs). This controller is the next-generation Replication Controller (rc). You can still find some applications using Replication Controller instead of ReplicaSets. The objective of ReplicaSets is to ensure that a specified number of pod replicas are running at any given time.
- Pods (po). A Pod is the basic building block of Kubernetes–the smallest and simplest unit in the Kubernetes object model that you create or deploy. A Pod represents a running process on your cluster. Since we didn’t define the number of ReplicaSets, for that reason it runs by default a single Pod. If you would like to see where the Pod is running on your cluster, you can run the same command with the flag -o wide (-o is output): kubectl get all -n webservers -o wide.
Kubernetes Namespaces are an important part of your platform and security. It will allow you to logically segregate and assign resources for each of them. Also, it creates a space where the object names don’t impact with the objects in other Kubernetes namespaces.