Table of contents

• Overview
• Compatibility Matrix
• Examples
• Usage
  • Creating a client
  • Configuring a client
  • Client authentication
  • Client DSL
  • Loading from external sources
  • Type-erased usage
  • CRD Support
• Metrics
• Installation
• License

Overview

Swift client for talking to a Kubernetes cluster via a fluent DSL based on SwiftNIO and the AysncHTTPClient.

• Covers all Kubernetes API Groups in v1.28.3
• Automatic configuration discovery
• DSL style API
  • For all API Groups/Versions
• Generic client support
• Swift-Logging support
• Loading resources from external sources
  • from files
  • from URLs
• Read Options
• List Options
• Delete Options
• PATCH API
• /scale API
• /status API
• Resource watch support
• Follow pod logs support
• Discovery API
• CRD support
• Controller/Informer support
• Swift Metrics
• Complete documentation
• End-to-end tests

Compatibility Matrix

• ✓ Exact match of API objects in both client and the Kubernetes version.
• - API objects mismatches either due to the removal of old API or the addition of new API. However, everything the
• client and Kubernetes have in common will work.

Examples

Concrete examples for using the Swiftkube tooling reside in the Swiftkube:Examples repository.

Usage

Creating a client

To create a client just import SwiftkubeClient and init an instance.

import SwiftkubeClient

let client = try KubernetesClient()

You should shut down the KubernetesClient instance when you're done using it, which in turn shuts down the underlying HTTPClient. Thus, you shouldn't call client.syncShutdown() before all requests have finished. You can also shut down the client asynchronously in an async/await context or by providing a DispatchQueue for the completion callback.

// when finished close the client
 try client.syncShutdown()
 
// async/await
try await client.shutdown()

// DispatchQueue
let queue: DispatchQueue = ...
client.shutdown(queue: queue) { (error: Error?) in 
    print(error)
}

Configuring the client

The client tries to resolve a kube config automatically from different sources in the following order:

• Kube config file in the user's $HOME/.kube/config directory
• ServiceAccount token located at /var/run/secrets/kubernetes.io/serviceaccount/token and a mounted CA certificate,
• if it's running in Kubernetes.

Alternatively it can be configured manually, for example:

let caCert = try NIOSSLCertificate.fromPEMFile(caFile)
let authentication = KubernetesClientAuthentication.basicAuth(
  username: "admin", 
  password: "admin"
)

let config = KubernetesClientConfig(
   masterURL: "https://kubernetesmaster",
   namespace: "default",
   authentication: authentication,
   trustRoots: NIOSSLTrustRoots.certificates(caCert),
   insecureSkipTLSVerify: false,
   timeout: HTTPClient.Configuration.Timeout.init(connect: .seconds(1), read: .seconds(10)),
   redirectConfiguration: HTTPClient.Configuration.RedirectConfiguration.follow(max: 5, allowCycles: false)
)

let client = KubernetesClient(config: config)

Client authentication

The following authentication schemes are supported:

• Basic Auth: .basicAuth(username: String, password: String)
• Bearer Token: .bearer(token: String)
• Client certificate: .x509(clientCertificate: NIOSSLCertificate, clientKey: NIOSSLPrivateKey)

Client DSL

SwiftkubeClient defines convenience API to work with Kubernetes resources. Using this DSL is the same for all resources.

The client exposes asynchronous functions using the new Swift concurrency model.

List resources

let namespaces = try await client.namespaces.list()
let deployments = try await client.appsV1.deployments.list(in: .allNamespaces)
let roles = try await client.rbacV1.roles.list(in: .namespace("ns"))

You can filter the listed resources or limit the returned list size via the ListOptions:

let deployments = try await client.appsV1.deployments.list(in: .allNamespaces, options: [
  .labelSelector(.eq(["app": "nginx"])),
  .labelSelector(.notIn(["env": ["dev", "staging"]])),
  .labelSelector(.exists(["app", "env"])),
  .fieldSelector(.eq(["status.phase": "Running"])),
  .resourceVersion("9001"),
  .limit(20),
  .timeoutSeconds(10)
])

Get a resource

let namespace = try await client.namespaces.get(name: "ns")
let deployment = try await client.appsV1.deployments.get(in: .namespace("ns"), name: "nginx")
let roles = try await client.rbacV1.roles.get(in: .namespace("ns"), name: "role")

You can also provide the following ReadOptions:

let deployments = try await client.appsV1.deployments.get(in: .allNamespaces, options: [
  .pretty(true),
  .exact(false),
  .export(true)
])

Delete a resource

try await client.namespaces.delete(name: "ns")
try await client.appsV1.deployments.delete(in: .namespace("ns"), name: "nginx")
try await client.rbacV1.roles.delete(in: .namespace("ns"), name: "role")

You can pass an instance of meta.v1.DeleteOptions to control the behaviour of the delete operation:

let deletOptions = meta.v1.DeleteOptions(
  gracePeriodSeconds: 10,
  propagationPolicy: "Foreground"
)
try await client.pods.delete(in: .namespace("ns"), name: "nginx", options: deleteOptions)

Create and update a resource

Resources can be created/updated directly or via the convenience builders defined in SwiftkubeModel

// Create a resource instance and post it
let configMap = core.v1.ConfigMap(
  metadata: meta.v1.ObjectMeta(name: "test"),
  data: ["foo": "bar"]
)
try cm = try await client.configMaps.create(inNamespace: .default, configMap)

// Or inline via a builder
let pod = try await client.pods.create(inNamespace: .default) {
   sk.pod {
     $0.metadata = sk.metadata(name: "nginx")
     $0.spec = sk.podSpec {
       $0.containers = [
         sk.container(name: "nginx") {
           $0.image = "nginx"
         }
       ]
     }
   }
}

Watch a resource

You can watch for Kubernetes events about specific objects via the watch API.

Watching resources opens a persistent connection to the API server. The connection is represented by a SwiftkubeClientTask instance, that acts as an active "subscription" to the events stream.

The task instance must be started explicitly via SwiftkubeClientTask/start(), which returns an AsyncThrowingStream, that starts yielding items immediately as they are received from the Kubernetes API server.

The async stream buffers its results if there are no active consumers. The AsyncThrowingStream.BufferingPolicy.unbounded buffering policy is used, which should be taken into consideration.

let task: SwiftkubeClientTask = client.pods.watch(in: .allNamespaces)
let stream = task.start()

for try await event in stream {
  print(event)
}

You can also pass ListOptions to filter, i.e. select the required objects:

let options = [
  .labelSelector(.eq(["app": "nginx"])),
  .labelSelector(.exists(["env"]))
]

let task = client.pods.watch(in: .default, options: options)

The client reconnects automatically and restarts the watch upon encountering non-recoverable errors. The reconnect-behaviour can be controlled by passing an instance of RetryStrategy.

The default strategy is 10 retry attempts with a fixed 5 seconds delay between each attempt. The initial delay is one second. A jitter of 0.2 seconds is applied.

Passing RetryStrategy.never disables any reconnection attempts.

let strategy = RetryStrategy(
  policy: .maxAttemtps(20),
  backoff: .exponentiaBackoff(maxDelay: 60, multiplier: 2.0),
  initialDelay = 5.0,
  jitter = 0.2
)
let task = client.pods.watch(in: .default, retryStrategy: strategy)

for try await event in task.stream() {
  print(event)
}

The task must be cancelled when it is no longer needed:

task.cancel()

Follow logs

The follow API resembles the watch, but instead of events, it emits the log lines.

:warning: The client does not reconnect on errors in follow mode.

let task = client.pods.follow(in: .default, name: "nginx", container: "app")

for try await line in task.start() {
  print(line)
}

// The task can be cancelled later to stop following logs
task.cancel()

Discovery

The client provides a discovery interface for the API server, which can be used to retrieve the server version, the API groups and the API resources for a specific group version.

let version: Info = try await client.discovery.serverVersion()
let groups: meta.v1.APIGroupList = try await client.discovery.serverGroups()
let resources: meta.v1.APIResourceList = try await client.discovery.serverResources(forGroupVersion: "apps/v1")

Loading from external sources

A resource can be loaded from a file or a URL:

// Load from URL, e.g. a file
let url = URL(fileURLWithPath: "/path/to/manifest.yaml")
let deployment = try apps.v1.Deployment.load(contentsOf: url)

Type-erased usage

Often when working with Kubernetes the concrete type of the resource is not known or not relevant, e.g. when creating resources from a YAML manifest file. Other times the type or kind of the resource must be derived at runtime given its string representation.

Leveraging SwiftkubeModel's type-erased resource implementations UnstructuredResource and its corresponding List-Type UnstructuredResourceList it is possible to have a generic client instance, which must be initialized with a GroupVersionResource type:

guard let gvr = try? GroupVersionResource(for: "deployment") else {
   // handle this
}

// Get by name
let resource: UnstructuredResource = try await client.for(gvr: gvr).get(in: .default , name: "nginx")

// List all
let resources: UnstructuredResourceList = try await client.for(gvr: gvr).list(in: .allNamespaces)

GroupVersionKind & GroupVersionResource

A GroupVersionKind & GroupVersionResource can be initialized from:

• KubernetesAPIResource instance
• KubernetesAPIResource type
• Full API Group string
• Lower-cased singular resource kind
• Lower-cased plural resource name
• Lower-cased short resource name

let deployment = ..
let gvk = GroupVersionKind(of: deployment)
let gvr = GroupVersionResource(of: deployment)
let gvk = GroupVersionKind(of: apps.v1.Deployment.self)
let gvr = GroupVersionResource(for: "configmaps")
let gvk = GroupVersionKind(for: "cm")
let gvr = GroupVersionResource(for: "cm")
// etc.

CRD Support

SwiftkubeClient supports Custom Resource Definitions (CRDs) natively. For example, a CRD manifest can be loaded from a YAML file or created programmatically, and then created via the client DSL:

let crd = apiextensions.v1.CustomResourceDefinition.load(contentsOf: URL(filePath: "/path/to/crd.yaml"))
try await client.apiExtensionsV1.customResourceDefinitions.create(crd)

The KubernetesClient can now be "extended", in order to manage the Custom Resources. One way would be to use the UnstructuredResource described in the previous section given some GroupVersionResource.

However, the client can work with any object that implement the relevant marker protocols, which allows for custom types to be defined and used directly.

Here is a complete example to clarify.

Given the following CRD:

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: crontabs.example.com
spec:
  group: example.com
  names:
    plural: crontabs
    singular: crontab
    kind: CronTab
    shortNames:
      - ct
  scope: Namespaced
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                cronSpec:
                  type: string
                image:
                  type: string
                replicas:
                  type: integer

The marker protocols are:

• KubernetesAPIResource marks the object as a Kubernetes resource that has a corresponding API endpoint
• NamespacedResource & ClusterScopedResource to indicate whether the resource is namespaced or cluster-scoped
• ReadableResource activates the get, list and watch API for the resource
• CreatableResource activates the create API for the resource
• ReplaceableResource activates the update API for the resource
• DeletableResource activates the delete API for the resource
• CollectionDeletableResource activate the deleteAll API for the resource
• ScalableResource activates the scale API for the resource
• MetadataHavingResource indicates, that the resource has a metadata field of type meta.v1.ObjectMeta?
• StatusHavingResource indicate, that the resource has a scale field (w/o assuming its type)

The following custom structs can be defined:

struct CronTab: KubernetesAPIResource, NamespacedResource, MetadataHavingResource, 
        ReadableResource, CreatableResource, ListableResource {
  typealias List = CronTabList
  var apiVersion = "example.com/v1"
  var kind = "CronTab"
  var metadata: meta.v1.ObjectMeta?
  var spec: CronTabSpec
}

struct CronTabSpec: Codable, Hashable {
  var cronSpec: String
  var image: String
  var replicas: Int
}

struct CronTabList: KubernetesResourceList {
  var apiVersion = "example.com/v1"
  var kind = "crontabs"
  var items: [CronTab]
}

Now, the new Custom Resource can be used like any other Kubernetes resource:

let gvr = GroupVersionResource(
  group: "example.com",
  version: "v1",
  resource: "crontabs"
)

let cronTabClient = client.for(CronTab.self, gvr: gvr)

let cronTab = CronTab(
  metadata: meta.v1.ObjectMeta(name: "new-cron"),
  spec: CronTabSpec(
    cronSpec : "* * * * */5",
    image: "some-cron-image",
    replicas: 2
  )
)

let new = try await cronTabClient.create(in: .default, cronTab)
let cronTabs: CronTabList = try await cronTabClient.list(in: .allNamespaces)

Metrics

KubernetesClient uses SwiftMetrics to collect metric information about the requests count and latencies.

The following metrics are gathered:

• sk_http_requests_total(counter): the total count of the requests made by the client.
• sk_http_request_errors_total(counter): the total number of requests made, that returned a http error.
• sk_request_errors_total(counter): the total number of requests that couldn't be dispatched due to non-http errors.
• sk_http_request_duration_seconds(timer): the complete request durations.

Collecting the metrics

To collect the metrics you have to bootstrap a metrics backend in your application. For example, you can collect the metrics to prometheus via SwiftPrometheus:

import Metrics
import Prometheus

let prom = PrometheusClient()
MetricsSystem.bootstrap(prom)

and expose a /metrics endpoint for scraping:

// if using vapor
app.get("metrics") { request -> EventLoopFuture<String> in
    let promise = request.eventLoop.makePromise(of: String.self)
    try MetricsSystem.prometheus().collect(into: promise)
    return promise.futureResult
}

Installation

To use the SwiftkubeClient in a SwiftPM project, add the following line to the dependencies in your Package.swift file:

.package(name: "SwiftkubeClient", url: "https://github.com/swiftkube/client.git", from: "0.18.0")

then include it as a dependency in your target:

import PackageDescription

let package = Package(
    // ...
    dependencies: [
        .package(name: "SwiftkubeClient", url: "https://github.com/swiftkube/client.git", from: "0.18.0")
    ],
    targets: [
        .target(name: "<your-target>", dependencies: [
            .product(name: "SwiftkubeClient", package: "SwiftkubeClient"),
        ])
    ]
)

Then run swift build.

License

Swiftkube project is licensed under version 2.0 of the Apache License. See LICENSE for more details.