What Is Kubernetes Pod Disrupt Budget ?

Kubernetes simplifies the management and deployment of containerized applications. However, it can also suffer from disruptions that need to be managed within the Kubernetes ecosystem. The Kubernetes Pod Disrupt Budget, just like other Kubernetes policies, allows us to manage the pod disruptions that we can come across while managing our applications within the Kubernetes Cluster.

In this article, we will dive deep into the concept of setting up the Kubernetes Pod Disrupt Budget so that disruptions in the Kubernetes Pods will not affect the application’s workflow.

What is Kubernetes pod disruption?

Kubernetes Pod disruptions refer to the intentional termination of pods within a Kubernetes cluster. Generally, this process occurs during cluster maintenance, node decommissioning, or resource optimization activities. When a pod disruption starts, Kubernetes handles the termination of pods. This ensures that the ongoing tasks are completed, and existing connections are terminated smoothly before the pod is removed from service.

This disruption can happen in several ways. First, let us understand them.

Types of Pod Disruption

• Voluntary Disruption: In this disruption, the administrators or automated processes terminate the pods for maintenance, scaling, or resource optimization. For example, the administrator may scale down the number of pods in response to reduced workload demands for routine maintenance tasks.

• Involuntary Disruption: These occur due to uncertain events or failures, such as node failures, hardware malfunctions, or network issues. Examples of this type of Pod Disruptions are events that are unplanned and occur due to hardware failures, software errors, or network outages due to which the pods become unavailable.

It’s now time to look at the Pod Disruption Budget that helps us to handle the Pod Disruption Budget.

Overview of Pod Disruption Budget (PDB)

The Pod Disruption Budget (PDB) is the resource management tool in Kubernetes that allows the administrators to control the impact of pod disruptions on application availability and reliability. PDBs enable administrators to define constraints on the number of pods that can be concurrently disrupted within a specified timeframe.

Therefore, by defining the appropriate disruption budgets, administrators can prevent excessive disruptions that cause service degradation or downtime during cluster maintenance or node failures. The following points highlight the Pod Disruption Budget in more detailed way:

• PDBs are configured at the namespace level and specify parameters such as the maximum number of disruptions allowed.
• They also define the minimum number of pods that must remain available during disruptions.
• Also, we can adjust them dynamically based on the workload priorities, resource utilization, and service level objectives (SLOs). Due to this, we can achieve operational efficiency along with the service reliability.

How Does the Pod Disruption Budget Work?

After understanding the Pod Disruption Budget, let us learn how the Pod Disruption Budget works. Through the following pointers, let us see the workflow of the PDB.

• First, the user creates the Pod Disruption Budget (PDB) manifest. It defines the desired constraints on pod disruptions within a specific namespace or across the entire cluster. Then the user PDB manifests to the Kubernetes cluster using the ‘kubectl apply.’
• When the voluntary disruption event occurs, Kubernetes detects the event and identifies the affected pods. Kubernetes then evaluates the constraints specified in the PDB manifest associated with the affected pods.
• After this, Kubernetes attempts to reschedule the pods onto available nodes in the cluster while ensuring that the constraints specified in the PDB are not violated.

After this, the Administrators can review logs, metrics, and event notifications to evaluate the effectiveness of the PDB constraints. This is done using the Kubernetes Monitoring and Reporting Mechanisms.

How to set up the Pod Disruption Budget in Kubernetes?

In the below steps, we will use the minikube to locally run the Kubernetes on our local machine.

Step 1: First, we have to create the PDB Manifests using YAML or JSON format. We have to define the desired constraints for pod disruptions like the maximum number of pods that can be disrupted simultaneously (maxUnavailable) and the minimum number of pods that must remain available (minAvailable).

Here, we will use the following YAML code in the test-pdb.yaml to set up the Pod Disruption Budget.

 apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: zk-pdb
spec:
  maxUnavailable: 1
  selector:
    matchLabels:
      app: zookeeper

Step 2: Now, apply the PDB manifest to the Kubernetes cluster using the command ‘kubectl apply -f pdb.yaml’ command. You should get the output as shown below.

Step 3: We have to verify that the PDB has been successfully created in the Kubernetes cluster. Use the ‘kubectl get pdb’ command to list all existing PDBs and confirm that the newly created PDB appears in the list as shown below.

Therefore, we have learned to set up the Pod Disruption Budget.

Benefits of the Kubernetes Pod Disruption

• It makes the application stable: It ensures the stability of the application by defining constraints on the number of pod disruptions allowed within a Kubernetes cluster. This increases the availability and reliability of our application.
• It provides fine-grained control over the applications: Administrators can specify constraints based on application dependencies, workload priorities, and service level objectives (SLOs). Hence, we get precise control over the application management.
• We can handle the Automatic Failover: It enables the Kubernetes system to automatically handle the failover by specifying the constraints that govern pod rescheduling and failover behavior.
• It allows users to monitor the cluster: PDB metrics and monitoring tools help us to track cluster health and identify areas for optimization or improvement. So, we can easily identify the areas for improvement.

Conclusion

The Kubernetes Pod Disruption Budget is crucial for ensuring the stability, resilience, and reliability of applications running on Kubernetes clusters. They allow the administrators to control the impact of maintenance activities, node failures, and resource optimizations on application availability. Not only this, but it also focuses on resource utilization, monitoring cluster health, and fulfilling service level agreements (SLAs). After gaining a clear understanding of the PDBs, you can easily handle your Kubernetes Applications.

Kubernetes pod disrupt budget – FAQ’s

What happens if a disruption exceeds the constraints specified in the Pod Disruption Budget?

If a disruption event exceeds the constraints specified in the Pod Disruption Budget, Kubernetes will delay or suspend the disruption until it can be executed within the specified limits. This ensures that the disruption remains limited within the policies defined in the PDBs.

What are the Limitations of the Pod Disruption Budget?

When we have to implement the Pod Disruption Budget for the StatefulSets or DaemonSets, we have to take care of many considerations for application consistency, data integrity, and workload distribution. StatefulSets manages stateful applications with persistent identities for their pods. On the other hand, the DaemonSets ensure that a copy of a pod runs on each node in the cluster. Therefore, they have their own mechanisms for handling the disruptions.

What is the use of the Namespaces in the Kubernetes Pod Disruption Budget?

Namespaces are the logical boundaries that encapsulate the Kubernetes resources including the PDBs. PDBs are typically defined within a specific namespace and cover the disruption policies according to the requirements of the applications.

Is Kubernetes open-source?

Kubernetes is an open-source container orchestration platform originally developed by Google and later donated to the Cloud Native Computing Foundation (CNCF). Thus it is freely available for anyone to use for managing containerized applications.

Is Kubernetes Cluster different from Node?

A Kubernetes cluster is a set of nodes (machines) that collectively run your containerized applications. It consists of one or more master nodes, which control the cluster and manage its state, and multiple worker nodes, which run the containers of the application. On the other hand, the node is a physical or virtual machine that serves as a worker machine in the Kubernetes cluster. So, we can say that Node is the building block of the Cluster.