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Understanding Namespaces in Kubernetes
8 min read

Understanding Namespaces in Kubernetes

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Introduction​

Namespaces in Kubernetes provide a scope for resource names and a way of isolating resources logically concerning a team, project, or environment. Sometimes this might not be necessary for small-scale clusters, but when teams start working together in an environment, such segregation becomes indispensable. This article is all about describing when and how to effectively use namespaces for resource efficiency and isolation.

We'll cover the following topics in this article:

Understanding the Role of Namespaces in Kubernetes​

Namespaces in Kubernetes provide a way to logically isolate resources residing within a cluster. If there are several teams or projects using the same cluster, it will be required that resources created by each team are identified by unique names relative to their namespace. That means teams can manage resources independently without needing to have concerns about naming conflicts.

Namespaces act as a boundary for access, as well as another resource quota management in environments with several teams. Quotas can be set well on resource utilization so that no single team 'eats up' all the available resources, hence keeping efficiency and a proper balance. For instance, if Team A has a big project and requires a lot of resources, while Team B is just doing some lightweight tasks, it will enable us to manage such scenarios without interference. But that doesn't mean we can skip good naming convention.

For minor differences, such as different software versions, we should use labels and not create separate namespace. As an example, I might run multiple versions of a service within one namespace, yet distinguish them with labels:

kubectl label deployment my-app version=v1.0
kubectl label deployment my-app version=v1.1

So here, even within the same namespace, we recognize each version clearly, and we keep everything tidy.

When to Implement Multiple Namespaces​

For example, in Kubernetes, multiple namespaces are required for big environments involving a lot of users and different teams because they provide a way of resource isolation. This is important when the cluster involves various teams working on several projects, preventing resource conflicts and making the management of resources easier.

Suppose there is team A, which is developing an application, and team B, which is doing testing parallel to team A. By creating a separate namespace for both teams, they would not affect each other's resources.

As each namespace defines its own scope for names, resources such as Deployments must be unique only within their namespace. It is important however to realize that to differentiate slight variations of resources - such as different versions of software for instance, adding labels are much better practice than the creation of further namespaces. For instance:

kubectl label deployment my-app version=v1.0
kubectl label deployment my-app version=v1.1

Labeling enables teams to manage versioning rather effectively without the overhead of extra namespaces, but it keeps things clear in the same workspace.

Kubernetes Initial and System Namespaces​

Kubernetes starts up with four essential namespaces: default, kube-node-lease, kube-public, and kube-system, each serving distinct functions in running the cluster.

  1. default: This is the namespace in which a user can immediately start using the cluster without actually creating a new namespace. This is mainly for ad-hoc testing, but not really recommended to deploy production workloads since there can be several resource clashes.

  2. kube-node-lease: This namespace is supposed to contain Lease objects, one per each node in the cluster. Through these leases, the kubelet is granted the ability to broadcast heartbeats, enabling the control plane to detect node failures efficiently. This helps a lot in working with nodes and checking their health status.

  3. kube-public: Resources in this namespace are readable by all clients, and do not require authentication. Conventional use is for cluster-wide information that is public in nature, though none is required.

  4. kube-system: This namespace is reserved for objects created by the Kubernetes system itself. It contains system daemons and other components necessary to function. Where possible, it is advisable not to use the default namespace in production environments for the workloads of the user; instead, create any application-specific namespace, which will grant better isolation and manageability in your cluster.

Overview Best Practices for Managing Namespaces​

Generally speaking, with Kubernetes namespace managing, a number of best practices could be followed in order to efficiently handle the resources and set organization well. The main guidelines are on naming convention where the prefix of 'kube-' must not be used for personalized namespaces. This is because this is a reserved prefix, which is utilized for system namespaces, and using it may cause confusion besides causing resource conflicts.

Creating and Managing Namespaces​

It is also very simple to create and delete namespaces using kubectl. In order to create a new namespace, one can do the following:

kubectl create namespace <namespace-name>

To delete a namespace do:

kubectl delete namespace <namespace-name>

You can list the existing namespaces in your cluster with:

kubectl get namespace

This command lists the current namespaces, thus giving an overview of how resources are organized.

Setting Namespace Preferences​

For the sake of resource management, you may want to set a default namespace for your kubectl context. This will save you from needing to specify the namespace when using each command. You can do so by using:

kubectl config set-context --current --namespace=<insert-namespace-name-here>

You can verify your change by checking the current configuration with:

kubectl config view --minify | grep namespace:

The adherence to these best practices will guarantee that the management of namespaces will be well-organized, hence improving collaboration and resource sharing between the different teams.

Namespaces and DNS Entries​

Services in Kubernetes work pretty closely with DNS to enable communication within the cluster. For every service that is created in a namespace, there is a corresponding creation of a DNS entry. This takes the form of <service-name>.<namespace-name>.svc.cluster.local>, so when a container refers to a service by name, it resolves to the right instance in its namespace.

This structure also helps, not only with internal communications, but in maintaining consistency across multiple environments like Development, Staging, and Production.

This introduces a risk of namespace collision with the public records: if a namespace happens to share a name with any of the public top-level domains, the services in that namespace can have DNS names conflicting with the existing records. Suppose there's a namespace named example. One may end up accidentally creating a DNS record for a service with an address matching some public service and end up accidentally redirecting people to the wrong endpoint. These risks can be mitigated by controlling who is allowed to create namespaces, a privilege given to only a few select trusted users of the system.

Third-party security systems such as admission webhooks prevent even the creation of a namespace with a name equal to a public TLD. We will sustain tight control over namespace naming and creation in order to use the DNS capability of Kubernetes without slipping into pitfalls related to namespace conflicts.

Namespace-scoped versus Cluster-scoped Resources​

In Kubernetes, one must differentiate between namespace-scoped resources and cluster-scoped resources, since this organization plays a significant role in ensuring good housekeeping of the resources. Namespace-scoped resources, like Deployments and Services, are confined to a given namespace; therefore, multiple teams can use the same name of the resources without conflict. However, cluster-scoped resources, like StorageClass, Nodes, and PersistentVolumes, do not fall into any namespace and are shared by the whole cluster.

Listing Namespaced and Non-Namespaced Resources​

You can use the following kubectl commands in order to understand which resources go into each category:

  1. List Namespaced Resources:

    kubectl api-resources --namespaced=true

    The command will return resources specific to a namespace, allowing you to see which resources are isolated in their respective namespaces.

  2. List Non-Namespaced Resources:

    kubectl api-resources --namespaced=false

    This command lists resources that are present outside of any namespace, driving home how abstract it stands apart at the cluster level.

Why Some Resources Are Not Namespaced​

Some resources are not created in any namespace because they represent cluster-wide functions that need to be reachable from everywhere, so all components of a Kubernetes cluster can work properly. For example, nodes need to be universally identifiable to perform scheduling, so they could not be confined to a namespace. Understanding the difference between these two resource types is basically at the heart of managing a Kubernetes cluster without running into resource conflict issues.

Conclusions​

The namespace feature in Kubernetes is indeed quite powerful in organizing resources effectively within a cluster. Being able to understand where and when to use them, and how to manage them effectively, ensures not only structures in resource allocation and isolation but forms the basis of teamwork, especially within large organizations that use many users or a number of projects. Instilling security best practices and proper naming conventions further enhance their utility. Full knowledge of the namespace significantly improves operational efficiency in the management of resources within cloud-native ecosystems.