Using Pod Disruption Budgets (PDB) in SAAP

Pod Disruption Budget (PDB) is a crucial tool for maintaining the availability and stability of your applications in SAAP during updates and disruptions. By setting the minimum and maximum pod availability, you can ensure that your application remains operational even in the face of cluster changes.

In this tutorial, you will learn how to use Pod Disruption Budget (PDB) to manage the availability and stability of your applications in SAAP during updates and maintenance activities. PDB help ensure that a minimum number of pods are available and operational at all times, reducing the risk of service disruptions.

Objectives

Enable replicas.
Configure a Pod Disruption Budget for an application deployed on SAAP.
Observe the behavior of the PDB by deleting a pod and analyzing the changes in PDB status.

Key Results

Successfully enable and monitor a Pod Disruption Budget for the application's deployment on SAAP.

Tutorial

Let's scale up the number of replicas to see how pdb works.

Add replicas: 3 in deploy/values.yaml.
```
# Scale up replicas
replicas: 3 # Number of replicas
```
It should look like this

Make sure autoscaling is enabled: false, or you can scale up the minReplicas to match the replicas, that way you don't need to disable autoscaling.

Note

The indentation should be application.deployment.replicas.

Enable pdb in your deploy/values.yaml file. Add the following YAML:

# Enable Pod Disruption Budget (PDB) for your application's pods.
  pdb:
    # Set PDB enabled to true to activate the Pod Disruption Budget.
    enabled: true
    # Specify the minimum number of available pods during disruptions. In this case, ensure at least 1 pod is available at all times.
    minAvailable: 2
    # Specify the maximum number of pods that can be unavailable simultaneously during disruptions
    maxUnavailable: 2

It should look like this:

PDB values

Look at the different colors that indicates indentation.

Note

The indentation should be application.pdb.

Save and run tilt up at the root of your directory. Hit the space bar and the browser with TILT logs will be shown. If everything is green then the changes will be deployed on the cluster.

Let's see the number of replicas.
Log in to SAAP. In your namespace check if the replicaSet has created the number of replicaCounts which is 3.
To check if pdb is created, switch to your namespace, go to Administrator > Home > Search and search for pdb.
Click on PodDisruptionBudget and see the newly created pdb named review.
Click on review pdb. Go to YAML, scroll down and see the status of pdb. Check out the status and currentHealthy: 3, desiredHealthy: 2 which satisfies the condition of minAvailable: 2. We can see the DisruptionAllowed status is true.
let's scale down the replicas to create a disruption and see if pdb works accurately.
```
oc scale deployment review --replicas=1 -n <your-namespace>
```
As soon as the replicas are scaled down, the pdb condition will enforce replicaSet to make sure the minimum replicas are available.
Delete the review pod and check the pdb status.
Go to pdb review, and check the status now. Click on reload. Now look at the currentHealthy: 1, which clearly shows that pdb is working fine.

As soon as the pods are recreated, pdb status will change to currentHealthy: 3 which meets the condition perfectly. Click on reload and you will see the updated status.

Remember that the behavior of the PDB and the speed at which it restores pod availability may be influenced by factors such as node resources, cluster conditions, and pod scheduling rules. It's important to give the system some time to react and observe how it gradually restores the desired number of healthy pods according to the PDB constraints.

Awesome! Let's move on to the next tutorial to add a network policy to your application.