Generic code

While having a specific ZIO module and strictly typed interface for each available Kubernetes resource, sometimes we want to write more generic functions:

  • that work on any given resource (maybe regardless of being namespaced or cluster level)
  • that work on a given capability for example on any resource having a scale subresource

This section shows the available tools for implementing such functions.

Generic layers

Every resource client module defines an alternative type alias called Generic.

For example the default Pods type is defined as the following:

type Pods = Has[Pods.Service]

and it's generic version, Pods.Generic defined in the companion object of Pods as:

type Generic = 
    Has[NamespacedResource[Pod]]
        with Has[NamespacedResourceStatus[PodStatus, Pod]]
        with Has[NamespacedLogSubresource[Pod]] 
        with Has[NamespacedEvictionSubresource[Pod]]
        with Has[NamespacedBindingSubresource[Pod]]

The pods layer can be converted to its Generic representation with .asGeneric:

import com.coralogix.zio.k8s.client.v1.pods.Pods
import com.coralogix.zio.k8s.client.K8sFailure

val pods: ZLayer[Blocking with System, Throwable, Pods] = k8sDefault >>> Pods.live
val generic: ZLayer[Blocking with System, Throwable, Pods.Generic] = pods.map(_.get.asGeneric)

This generic layer can be provided to generic functions that work with any kind of resource:

import com.coralogix.zio.k8s.client._
import com.coralogix.zio.k8s.client.model.K8sNamespace
import com.coralogix.zio.k8s.client.impl.ResourceClient
import zio._
import zio.console.Console

def getAndPrint[T : Tag](name: String, namespace: K8sNamespace): ZIO[Console with Has[NamespacedResource[T]], K8sFailure, Unit] =
    for {
        obj <- ResourceClient.namespaced.get(name, namespace)
        _ <- console.putStrLn(obj.toString).ignore
    } yield ()

K8sObject

Not knowing anything about the resource type in these generic functions is very limiting. There are a couple of type classes available implemented by the Kubernetes model classes that can be used in these scenarios.

K8sObject

The K8sObject type class provides access to the object's metadata, that always have the type ObjectMeta, and some other helper functions to get parts of this metadata and to manipulate ownership.

For example the above example can be extended to print the object's UID instead:

import com.coralogix.zio.k8s.client.model.K8sObject
import com.coralogix.zio.k8s.client.model.K8sObject._

def getAndPrintUid[T : Tag : K8sObject](name: String, namespace: K8sNamespace): ZIO[Console with Has[NamespacedResource[T]], K8sFailure, Unit] =
    for {
        obj <- ResourceClient.namespaced.get(name, namespace)
        uid <- obj.getUid
        _ <- console.putStrLn(uid).ignore
    } yield ()

K8sObjectStatus

Similarily to K8sObject, the K8sObjectStatus type class provides access to the resouce's status subresource. It is parametrized by both the resouce type and the status type:

trait K8sObjectStatus[ResourceT, StatusT]

Resource metadata

Finally each resource model class has an implicit ResourceMetadata value as well. This can be used to get information about the underlying resource's group/version/kind.

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