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Kubernetes Scheduling Features Or How Can I Make the System Do What I Want? Ian Lewis, Developer Advocate, Google

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Scheduling ?

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Scheduling Predicates Priorities

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Scheduling Predicates

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Scheduling Priorities 10 5

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Scheduling

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Scheduling Predicates Priorities

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Predicates deep dive

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Prevent overcommit ?

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Prevent overcommit ?

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Prevent co-scheduling (pod anti-affinity) ?

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Prevent co-scheduling (pod anti-affinity)

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Prevent co-scheduling (pod anti-affinity) ? PodAntiAffinity: { TopologyKey: "hostname", LabelSelector: "type:cat" }

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Prevent co-scheduling (pod anti-affinity)

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Prevent co-scheduling (pod anti-affinity)

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Prevent co-scheduling (pod anti-affinity)

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Prevent co-scheduling (pod anti-affinity)

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Prevent co-scheduling (pod anti-affinity) PodAntiAffinity: { TopologyKey: "hostname", LabelSelector: "type:cat" }

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Force co-scheduling (pod affinity) ?

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Force co-scheduling (pod affinity) ? PodAffinity: { TopologyKey: "hostname", LabelSelector: "type:sapling" }

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Force co-scheduling (pod affinity)

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Dedicated machines (Taints)

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Dedicated machines (Taints)

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Dedicated machines (Taints) Taint: { TaintEffect: "NoSchedule", Key: "color", Value: "blue" } Toleration: { Key: "color", Value: "blue", Operator: "Equal", TaintEffect: "NoSchedule" }

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Dedicated machines (Taints)

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Predicate summary ● Prevent overcommit ● Prevent co-scheduling ● Force co-scheduling ● Dedicated Nodes

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Priorities deep dive

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Best fit vs worst fit ?

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Best fit vs worst fit Worst fit

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Best fit vs worst fit Best fit

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Selector Spreading ?

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Selector Spreading

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Node Affinity ?

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Node Affinity

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Pod Affinity ?

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Pod Affinity

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Pod Anti-Affinity ?

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Pod Anti-Affinity

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How to combine scores? ?

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Linear combination Σa i p i

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https://commons.wikimedia.org/wiki/File:Messina_Straits_Chauliodus_sloani.jpg Dangers of depending on priorities

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Decision tree Node Affinity score Node Affinity score ? Spreading score Spreading score ? ... > < = 1000 * (Node Affinity score) + 100 * (Spreading score) + ... > < =

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Priorities are powerful … but require deep understanding

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• [beta in 1.6] Multi-scheduler support • [beta in 1.6] Node affinity • [beta in 1.6] Pod affinity/anti-affinity • [beta in 1.6] Tains & tolerations Feature state as of 1.6

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• Priorities & preemptions • Rescheduler • Resource estimation Future plans

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SIG Scheduling • Meeting every other Monday 2pm PST • #sig-scheduling Slack channel • kubernetes-sig-scheduling@ mailing group Join community