Kubernetes/Scheduling
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Default scheduler rules
- Identify if a node has adequate hardware resources
- Check if a node is running out of resources. check for memory or disk pressure conditions
- Check if a pod schedule is scheduled to a node by a name
- Check if a node has a label matching node selector in a pod spec
- Check if a pod is requesting to bound to a specific host port and if so, does the node have that port available
- Check if a pod is requesting a certain type of volume be mounted and if other pods are using the same volume
- Check if a pod tolerates taints of the node, eg. master nodes is tainted with "noSchedule"
- Check if a pod or a node affinity rules and checking if scheduling the pod would break these rules
- 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