Nimendra's Notes 🪴

Scheduling

2 min read

kubernetes kubernetes/cka

Labels, Selectors & Annotations
Taints & Toleration
Resource Limits
Multiple Schedulers
Daemonsets
StatefulSets
Node Selectors & Node Affinity

Core Idea

The scheduler normally picks a node by filling in nodeName through a binding object, but you can bypass it and place a pod yourself by setting nodeName (or creating a Binding) when there is no scheduler.

  • Manual scheduling: set spec.nodeName: node01 at creation, or POST a Binding resource pointing the pod at a target node.
  • Placement controls around the scheduler: labels and selectors, taints and tolerations, node selectors and affinity, multiple schedulers, DaemonSets, and StatefulSets.
  • The default path and the manual path both end with the pod running on exactly one node.

Manual Scheduling

Kubernetes manual scheduling refers to the process where a Kubernetes administrator manually assigns a pod to a specific node in the cluster, bypassing the Kubernetes scheduler’s automatic placement or No scheduler’s environment.

apiVersion: v1
kind: Pod
metadata:
  name: manual-scheduled-pod
spec:
  containers:
  - name: nginx
    image: nginx
  nodeName: node01  # <-- Specify the target node

How Scheduling Works

  • What do you do when you do not have a scheduler in your cluster?

    • Every POD has a field called NodeName that by default is not set. You don’t typically specify this field when you create the manifest file, kubernetes adds it automatically.

    • Once identified it schedules the POD on the node by setting the nodeName property to the name of the node by creating a binding object.

      apiVersion: v1
kind: Pod
metadata:
 name: nginx
 labels:
  name: nginx
spec:
 containers:
 - name: nginx
   image: nginx
   ports:
   - containerPort: 8080
 nodeName: node02

No Scheduler

  • You can manually assign pods to node itself. Well without a scheduler, to schedule pod is to set nodeName property in your pod definition file while creating a pod.

  • Another way
    apiVersion: v1
    kind: Binding
    metadata:
      name: nginx
    target:
      apiVersion: v1
      kind: Node
      name: node02
    apiVersion: v1
    kind: Pod
    metadata:
     name: nginx
     labels:
      name: nginx
    spec:
     containers:
     - name: nginx
       image: nginx
       ports:
       - containerPort: 8080

K8s Reference Docs:

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