Middleware

This guide covers the middleware stack that transforms a single Deployment declaration into a fully-configured stack.

The Middleware Stack

manifest = Kube::Cluster::Manifest.new(
  Kube::Cluster["Deployment"].new {
    metadata.name = "web"
    metadata.labels = {
      "app.kubernetes.io/expose": "app.example.com",
      "app.kubernetes.io/autoscale": "2-10",
      "app.kubernetes.io/size": "small"
    }
    spec.selector.matchLabels = { app: "web" }
    spec.template.spec.containers = [
      { name: "web", image: "nginx", ports: [{ name: "http", containerPort: 8080 }] }
    ]
  }
)

Kube::Cluster::Middleware::Stack.new {
  use Middleware::ServiceForDeployment
  use Middleware::IngressForService
  use Middleware::HPAForDeployment
  use Middleware::Namespace, "production"
  use Middleware::Labels, managed_by: "kube_cluster"
  use Middleware::ResourcePreset
  use Middleware::SecurityContext
  use Middleware::PodAntiAffinity
}.call(manifest)

puts manifest.to_yaml  # => Deployment, Service, Ingress, HPA -- all configured

Available Middleware

Middleware	Effect
`Namespace`	Sets `metadata.namespace` on all resources
`Labels`	Merges standard Kubernetes labels
`Annotations`	Merges annotations
`ResourcePreset`	Injects CPU/memory from `app.kubernetes.io/size` (nano to 2xlarge)
`SecurityContext`	Injects restricted/baseline security contexts
`PodAntiAffinity`	Spreads pods across nodes
`ServiceForDeployment`	Generates Service from named container ports
`IngressForService`	Generates Ingress from `app.kubernetes.io/expose` label
`HPAForDeployment`	Generates HPA from `app.kubernetes.io/autoscale` label