How to Add Roles to Nodes in Kubernetes

1. Overview

Nodes form the backbone of our Kubernetes cluster, providing the resources to run workloads and maintain cluster operations. Assigning specific roles to these nodes streamlines their responsibilities, whether they manage control plane tasks, handle our workloads, or perform specialized operations.

In this tutorial, we’ll explore how to assign roles to Kubernetes nodes and utilize them effectively for a more organized and efficient cluster.

2. Understanding Node Roles

Each node in Kubernetes can play a specific role within the cluster. These roles are vital for defining the node’s purpose and optimizing workload placement. Let’s explore the most common roles:

• Control Plane Nodes: These nodes manage the cluster’s overall state and coordinate tasks like scheduling, networking, and storing configuration data
• Worker Nodes: Worker nodes host the pods and containers running our applications, providing the computing and storage resources needed for workloads
• Specialized Nodes: Nodes with specific roles handle tasks like machine learning, logging, or storage, ensuring dedicated resources for specialized operations

Assigning roles provides clarity and ensures workloads land on the most suitable nodes, improving cluster efficiency and maintainability.

2.1. Why Assign Roles?

Assigning roles to nodes is essential for optimizing our Kubernetes cluster’s functionality. Here’s why it matters:

• Streamline Workload Placement: when we assign specific roles to our nodes, we ensure workloads are placed on the right ones, with the right resources for the tasks they need to handle
• Optimize Resources: by assigning roles, we can maximize the use of our nodes with specialized capabilities, like high-performance GPUs or extra storage; this way, our resources don’t sit idle, and workloads get exactly what they need to run smoothly and efficiently
• Simplify Cluster Management: when we define clear roles, managing our cluster becomes much easier; we can quickly identify which nodes are handling specific tasks, avoiding any confusion when we need to scale or troubleshoot – this clarity helps keep our operations smooth and ensures we can resolve issues faster

3. Assigning Roles to Nodes

We use labels to assign roles to nodes in Kubernetes. These labels act as identifiers that determine the purpose of each node. Kubernetes relies on these labels to schedule workloads appropriately. By labeling nodes, we create a more organized cluster and improve workload distribution. Let’s look at how to manage roles step by step.

3.1. Checking Existing Nodes

Before assigning roles, it’s a good idea to look at the current state of the nodes in our cluster. This gives us a clear picture of their setup and helps ensure roles are assigned effectively. To get started, we can run:

$ kubectl get nodes
NAME               STATUS   ROLES                  AGE   VERSION
control-plane-1    Ready    control-plane,master   3d    v1.28.1
ops-worker         Ready    <none>                 2d    v1.28.1

Here, we see ops–worker has no assigned roles, indicated by <none> in the ROLES column. Reviewing this information ensures we’re starting from a clear baseline.

3.2. Adding a Role to a Node

Assigning a role to a node involves adding a label identifying its purpose within the cluster. Labels help Kubernetes recognize and manage nodes based on their designated tasks. For instance, to assign a gpu role to ops-worker, we can use the following command:

$ kubectl label node ops-worker node-role.kubernetes.io/gpu=
node/ops-worker labeled

This command assigns the gpu label to the ops-worker node, marking it as suitable for GPU-based workloads. Once the command is executed, Kubernetes recognizes the node’s new role.

3.3. Verifying the Role

After labeling a node, we should verify that the changes took effect. To confirm the role is applied, we can recheck the node list using the get nodes command:

$ kubectl get nodes
NAME               STATUS   ROLES                  AGE   VERSION
control-plane-1    Ready    control-plane,master   3d    v1.28.1
ops-worker         Ready    gpu                    2d    v1.28.1

The gpu role now appears in the ROLES column for ops-worker. This confirms that the label has been applied successfully.

3.4. Assigning Multiple Roles

In some cases, a node may need to take on multiple responsibilities. For instance, if we want our ops-worker also to handle storage tasks, we can assign an additional role with the following command:

$ kubectl label node node-worker-1 node-role.kubernetes.io/storage=
node/ops-worker labeled

After running this command, the node will have both the gpu and storage roles. Let’s run this command to verify the update:

$ kubectl get nodes
NAME               STATUS   ROLES                       AGE   VERSION
control-plane-1    Ready    control-plane,master        3d    v1.28.1
ops-worker         Ready    gpu,storage                 2d    v1.28.1

This demonstrates how we can expand a node’s responsibilities with additional roles.

3.5. Changing a Role on a Node

Sometimes, we may decide to change the role assigned to a node. This could be due to a shift in the node’s responsibilities or a change in workload requirements. Kubernetes allows us to update an existing role by using the –overwrite option, which lets us replace the current label with a new one.

Assuming, we want to change the gpu role on ops-worker to a cpu role, we can run the following command:

$ kubectl label --overwrite node ops-worker node-role.kubernetes.io/gpu- node-role.kubernetes.io/cpu=
node/ops-worker labeled

In this command, we used the –overwrite option to ensure that the new label replaces the old one. After running this, ops-worker will be marked with the cpu role instead of the gpu role.

3.6. Removing a Role from a Node

If a node no longer requires a specific role, we can easily remove it. For instance, to delete the cpu role from our ops-worker node, we can run the following command:

$ kubectl label node ops-worker node-role.kubernetes.io/cpu-
node/ops-worker labeled

The hyphen (-) at the end of the label is crucial; it indicates that the label should be removed from the node. Without it, the command would attempt to assign or update the label instead.

To confirm the change, we can recheck the node list to ensure the role has been successfully removed:

$ kubectl get nodes
NAME               STATUS   ROLES         AGE   VERSION
control-plane-1    Ready    control-plane 3d    v1.28.1
ops-worker         Ready    storage       2d    v1.28.1

4. Best Practices

Making the most of our Kubernetes cluster starts with using node roles effectively. When we follow a few key practices, we can keep our cluster running smoothly, scale effortlessly, and manage it with ease. Let’s explore some simple ways to optimize our node roles:

By incorporating these best practices, we can ensure our cluster remains efficient and adaptable, even as our workloads and priorities evolve.

5. Conclusion

In this article, we explored how to assign roles to Kubernetes nodes, from listing nodes to labeling them with specific roles. We also looked at how these roles improve workload scheduling and shared best practices for effective cluster management.

By assigning roles, we can better organize our Kubernetes clusters, optimize resources, and streamline operations. These steps ensure our clusters remain efficient, well-structured, and capable of handling diverse workloads effectively.