From Ever changing code
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.
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 and resources
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 ...
YAML to schedule request to a specific node and request specific resources
apiVersion: v1 kind: Pod metadata: name: resource-pod1 spec: nodeSelector: kubernetes.io/hostname: "worker-2.acme.com" containers: - image: busybox command: ["dd", "if=/dev/zero", "of=/dev/null"] name: budybox-dd resources: requests: cpu: 800m #mili cores -> 2000m (large for 2nd deployment) memory: 20Mi #Mb
kubectl describe nodes worker-2.acme.com Non-terminated Pods: (6 in total) Namespace Name CPU Requests CPU Limits Memory Requests Memory Limits AGE --------- ---- ------------ ---------- --------------- ------------- --- default busybox 0 (0%) 0 (0%) 0 (0%) 0 (0%) 24h default nginx-loadbalancer-86bb844fb7-bl5fs 0 (0%) 0 (0%) 0 (0%) 0 (0%) 2d default resource-pod1 800m (40%) 0 (0%) 20Mi (0%) 0 (0%) 6m7s kube-system kube-flannel-ds-amd64-97hvr 100m (5%) 100m (5%) 50Mi (1%) 50Mi (1%) 14d kube-system kube-proxy-fxl6f 0 (0%) 0 (0%) 0 (0%) 0 (0%) 14d rbac1 test-f57db4bfd-ghshj 0 (0%) 0 (0%) 0 (0%) 0 (0%) 12d Allocated resources: (Total limits may be over 100 percent, i.e., overcommitted.) Resource Requests Limits -------- -------- ------ cpu 900m (45%) 100m (5%) memory 70Mi (1%) 50Mi (1%) ephemeral-storage 0 (0%) 0 (0%)
Then deploying another pod, requesting 2000mi cpus, will end up with scheduling error when describing the pod
kubectl describe pod pod2-2000mi-cpu Events: Type Reason Age From Message ---- ------ ---- ---- ------- Warning FailedScheduling 44s (x10 over 4m57s) default-scheduler 0/3 nodes are available: 2 node(s) didn't match node selector, 3 Insufficient cpu.
Limits YAML, Unlike requests, limits can go above total utilisation of CPU and memory. K8s will detect if overcommitted and kill the pod. Be aware Containers within pods are not aware of limits sets to pods, this can be seen from
top command within a container.
apiVersion: v1 kind: Pod metadata: name: pod-limit-resources spec: containers: - image: busybox command: ["dd", "if=/dev/zero", "of=/dev/null"] name: main resources: limits: cpu: 2 #by default requests are eq limits if not specified memory: 40Mi #
A DaemonSet ensures that all (or some) Nodes run a copy of a Pod. As nodes are added to the cluster, Pods are added to them. As nodes are removed from the cluster, those Pods are garbage collected. Deleting a DaemonSet will clean up the Pods it created. DaemonSets do not use a scheduler to deploy pods, DS used to ignore nodes taints. Some typical uses of a DaemonSet are:
- running a cluster storage daemon, such as glusterd, ceph, on each node.
- running a logs collection daemon on every node, such as fluentd or logstash.
- running a node monitoring daemon on every node, such as Prometheus Node Exporter, collectd
Monitor events and logs
kubectl get events --all-namespaces kubectl get events --watch #short -w #See scheduler logs kubectl logs [kube_scheduler_pod_name] -n kube-system tail -f /var/log/kube-scheduler.log #run on control plane node