Kubernetes/Scheduling

Default scheduler rules

1. Identify if a node has adequate hardware resources
2. Check if a node is running out of resources. check for memory or disk pressure conditions
3. Check if a pod schedule is scheduled to a node by a name
4. Check if a node has a label matching node selector in a pod spec
5. Check if a pod is requesting to bound to a specific host port and if so, does the node have that port available
6. Check if a pod is requesting a certain type of volume be mounted and if other pods are using the same volume
7. Check if a pod tolerates taints of the node, eg. master nodes is tainted with "noSchedule"
8. Check if a pod or a node affinity rules and checking if scheduling the pod would break these rules
9. If there is more than one node could schedule a pod, the scheduler priorities the nodes and choose the best one. If they have the same priority it chooses in round-robin fashion.

Label nodes

kubectl label node worker1.acme.com share-type=dedicated

YAML for the deployment to include the node affinity rules:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: pref
spec:
  replicas: 5
  template:
    metadata:
      labels:
        app: pref
    spec:
      affinity:
        nodeAffinity:
          preferredDuringSchedulingIgnoredDuringExecution: #all pods,but not current pod on the node
          - weight: 80
            preference:
              matchExpressions:
              - key: availability-zone
                operator: In
                values:
                - zone1
          - weight: 20              #4 time less priority then AZ
            preference:
              matchExpressions:
              - key: share-type     #label key
                operator: In
                values:
                - dedicated         #label value
      containers:
      - args:
        - sleep
        - "999"
        image: busybox:v1.28.4
        name: main

Capacity

Check node's capacity

kubectl describe nodes worker-2.acme.com | grep -A 20 Capacity:
Capacity:
 cpu:                2
 ephemeral-storage:  20263528Ki
 hugepages-2Mi:      0
 memory:             4044936Ki
 pods:               110
Allocatable:
 cpu:                2
 ephemeral-storage:  18674867374
 hugepages-2Mi:      0
 memory:             3942536Ki
 pods:               110
System Info:
 Machine ID:                 ******c49b4bed31684a******
 System UUID:                ******-D110-CB50-EAA3-*******
 Boot ID:                    ****8-be21-45ca-b86c-311a479******
 Kernel Version:             4.4.0-1087-aws
 OS Image:                   Ubuntu 16.04.6 LTS
 Operating System:           linux
 Architecture:               amd64
 Container Runtime Version:  docker://18.6.1

Resources

• Assigning a Pod to a Node
• Pod and Node Affinity Rules
• Configure Multiple Schedulers (our-own)