Question: How can I ensure that a Kubernetes pod is scheduled only on specific nodes, for instance, with SSD storage or with specific taints?

Answer: To ensure that a Kubernetes pod is scheduled only on specific nodes, you can combine node affinity and taints and tolerations. Here’s how to implement these features:

1. Node Affinity

Node affinity allows you to constrain which nodes your pod can be scheduled on based on node labels.

Steps:

1. Label Your Nodes:

   • Identify Nodes: List your nodes to identify which ones have the desired characteristics (e.g., SSD storage).

       kubectl get nodes
     

   • Add Labels: Label the nodes accordingly. For example, label nodes with SSD storage:

       kubectl label nodes <node-name> disktype=ssd
     

2. Define Node Affinity in Pod Specification:

   • Create Pod YAML: Add node affinity rules to your pod configuration YAML to target nodes with specific labels.

       apiVersion: v1
       kind: Pod
       metadata:
         name: my-pod
       spec:
         containers:
         - name: my-container
           image: nginx  # Example container image
         affinity:
           nodeAffinity:
             requiredDuringSchedulingIgnoredDuringExecution:
               nodeSelectorTerms:
               - matchExpressions:
                 - key: disktype
                   operator: In
                   values:
                   - ssd
     

   • Apply Configuration: Save the YAML file (e.g., pod-affinity.yaml) and apply it to your cluster:

       kubectl apply -f pod-affinity.yaml
     

2. Taints and Tolerations

Taints and tolerations ensure that pods are only scheduled on nodes with specific conditions.

Steps:

1. Add Taints to Nodes:

   • Apply Taints: Add taints to nodes to restrict which pods can be scheduled on them. For example:

       kubectl taint nodes <node-name> key=value:NoSchedule
     

   • Verify Taints: Check that the taint has been applied:

       kubectl describe node <node-name>
     

2. Define Tolerations in Pod Specification:

   • Update Pod YAML: Add tolerations to your pod YAML to allow scheduling on nodes with specific taints.

       apiVersion: v1
       kind: Pod
       metadata:
         name: my-pod
       spec:
         containers:
         - name: my-container
           image: nginx  # Example container image
         tolerations:
         - key: "key"
           operator: "Equal"
           value: "value"
           effect: "NoSchedule"
     

   • Apply Configuration: Save the updated YAML file (e.g., pod-tolerations.yaml) and apply it:

       kubectl apply -f pod-tolerations.yaml
     

Summary:

1. Label Nodes: Use kubectl label nodes <node-name> key=value to label nodes based on their characteristics.

2. Node Affinity: Define node affinity in the pod YAML file to schedule pods on nodes with specific labels.

3. Add Taints to Nodes: Use kubectl taint nodes <node-name> key=value:effect to apply taints to nodes.

4. Define Tolerations: Add tolerations to the pod YAML to allow it to be scheduled on tainted nodes.

By using node affinity and taints/tolerations, you can control the placement of your pods based on the hardware or configuration of your nodes.