Quality of Service (QoS) in Kubernetes: Ensuring Reliable Application Performance

In a busy Kubernetes cluster, important applications, especially those in critical sectors like financial services, can face slowdowns or failures if resources are tied up by less important tasks. Kubernetes Quality of Service (QoS) addresses this by prioritizing applications according to their resource requirements. This ensures that essential services receive resources first, maintaining smooth and stable operation even when resources are limited.

This blog will walk you through the key concepts and best practices for managing QoS in Kubernetes, making it easy to understand and implement.

• What is Quality of Service (QoS)?
• The Three QoS Classes
  • Guaranteed
  • Burstable
  • Best Effort
• How Kubernetes Manages QoS
• Benefits of Using QoS in Kubernetes
• Best Practices for Managing QoS in Kubernetes
• Conclusion

What is Quality of Service (QoS)?

Quality of Service (QoS) in Kubernetes is a way to manage and prioritize the resources used by containers running within a cluster. It ensures that critical applications receive the necessary resources and maintains the stability and efficiency of the system. Kubernetes classifies pods into three QoS classes based on their resource requirements: Guaranteed, Burstable, and Best Effort.

The Three QoS Classes

1. Guaranteed:

   Guaranteed pods receive the highest priority. Kubernetes ensures that every container in these pods has the same resource request and limit for CPU and memory. This guarantees that the pods will be scheduled and run with the requested resources, making them ideal for critical applications.

   Example for Guaranteed pods:
   

   apiVersion: v1
   kind: Pod
   metadata:
     name: guaranteed-pod
   spec:
     containers:
     - name: myapp-container
       image: myapp:latest
       resources:
         requests:
           memory: "1Gi"
           cpu: "500m"
         limits:
           memory: "1Gi"
           cpu: "500m"
   
   

2. Burstable

   Burstable pods have at least one container with resource requests but no matching limits. Kubernetes gives them medium priority, allowing them to burst up to the specified limits when resources are available. This makes them suitable for applications that need to run consistently but can tolerate some variability in resource allocation.

   
   Example for Burstable pods:

   apiVersion: v1
   kind: Pod
   metadata:
     name: burstable-pod
   spec:
     containers:
     - name: myapp
       image: myapp:latest
       resources:
         limits:
           memory: "1Gi"
           cpu: "1"
         requests:
           memory: "500Mi"
           cpu: "0.5"

3. BestEffort

   BestEffort pods have no resource requests or limits. Kubernetes gives them the lowest priority and schedules them only when resources are available. Under resource pressure, it evicts these pods first, making them suitable for non-critical workloads.

   

   Example for BestEffort pods :

   apiVersion: v1
   kind: Pod
   metadata:
     name: besteffort-pod
   spec:
     containers:
     - name: myapp
       image: myapp:latest
       resources: {}

To know more about Kubernetes Pods, click here.

How Kubernetes Manages QoS

Kubernetes uses QoS classes to decide scheduling and eviction. During scheduling, Guaranteed pods get preference. In resource contention, Best-Effort pods are evicted first, followed by Burstable pods. Guaranteed pods are evicted last, ensuring critical applications keep running.

Benefits of Using QoS in Kubernetes

• Resource Efficiency: By categorizing pods based on resource requirements, Kubernetes can allocate resources more efficiently, thereby preventing resource starvation.
• Reliability: Consequently, critical applications get the resources they need, which enhances the reliability and stability of the system.
• Cost Management: Moreover, by efficiently utilizing resources, organizations can optimize their infrastructure costs.

Best Practices for Managing QoS in Kubernetes

• Define Resource Requests and Limits: To begin with, always define resource requests and limits for your pods to ensure they are classified into appropriate QoS classes.
• Monitor Resource Usage: Furthermore, use monitoring tools to track resource usage and adjust requests and limits as needed.
• Prioritize Critical Applications: In addition, ensure that critical applications are in the Guaranteed class to avoid disruptions.
• Review and Adjust Regularly: Finally, regularly review your QoS settings and adjust them based on application performance and resource availability.

Also check: Everything you need to know about CKA Certification

Conclusion

Quality of Service in Kubernetes is a powerful tool for managing resources and ensuring the smooth operation of your applications. By understanding and implementing QoS, you can enhance the performance, reliability, and efficiency of your Kubernetes clusters. Whether you are running critical applications or handling variable workloads, QoS helps you maintain control and optimize your infrastructure.

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