Class: Kube::Cluster::Middleware::PodAntiAffinity

Inherits:
Kube::Cluster::Middleware show all
Defined in:
lib/kube/cluster/middleware/pod_anti_affinity.rb

Overview

Injects soft pod anti-affinity on pod-bearing resources so that pods prefer to spread across nodes.

The anti-affinity uses the resource’s own matchLabels from spec.selector.matchLabels as the label selector, and kubernetes.io/hostname as the topology key.

Resources that already have spec.template.spec.affinity set are left untouched.

stack do
  use Middleware::PodAntiAffinity
  use Middleware::PodAntiAffinity, topology_key: "topology.kubernetes.io/zone"
end

Instance Method Summary collapse

Constructor Details

#initialize(topology_key: "kubernetes.io/hostname", weight: 1) ⇒ PodAntiAffinity

Returns a new instance of PodAntiAffinity.



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# File 'lib/kube/cluster/middleware/pod_anti_affinity.rb', line 22

def initialize(topology_key: "kubernetes.io/hostname", weight: 1)
  @topology_key = topology_key
  @weight = weight
end

Instance Method Details

#call(manifest) ⇒ Object 



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# File 'lib/kube/cluster/middleware/pod_anti_affinity.rb', line 27

def call(manifest)
  manifest.resources.map! do |resource|
    next resource unless resource.pod_bearing?

    h = resource.to_h
    pod_spec = resource.pod_template(h)
    next resource unless pod_spec

    # Don't overwrite existing affinity configuration.
    next resource if pod_spec[:affinity]

    match_labels = h.dig(:spec, :selector, :matchLabels)
    next resource unless match_labels && !match_labels.empty?

    pod_spec[:affinity] = {
      podAntiAffinity: {
        preferredDuringSchedulingIgnoredDuringExecution: [
          {
            weight: @weight,
            podAffinityTerm: {
              labelSelector: { matchLabels: match_labels },
              topologyKey: @topology_key,
            },
          },
        ],
      },
    }

    resource.rebuild(h)
  end
end