Swiftkube:ServiceDiscovery

An implementation of the Swift Service Discovery API for Kubernetes based on SwiftkubeClient.

Table of contents

• Overview
• Usage
• RBAC
• Installation
• License

#Overview

• Auto-configuration for different environments
• Support for all K8s ListOptions
• Support for reconnect and retry
• Discovery for K8s Pod objects
• Discovery for K8s Service objects
• Complete documentation
• End-to-end tests

Usage

Creating a service discovery

To use this service discovery import SwiftkubeServiceDiscovery and init an instance.

import SwiftkubeServiceDiscovery

let discovery = KubernetesServiceDiscovery()

Underneath, SwiftkubeServiceDiscovery uses SwiftkubeClient for all Kubernets communication, which configures itself automatically for the environement it runs in.

You can also pass an existing client instance to the service discovery:

let client = KubernetesClient()
let discovery = KubernetesServiceDiscovery(client: client)

You should shut down the SwiftkubeServiceDiscovery instance, which in turn shuts down the underlying SwiftkubeClient. You can shutdown either in a synchronius way or asynchronously by providing a DispatchQueue for the completion callback.

// when finished close the client
 try discovery.syncShutdown()
 
// or asynchronously
let queue: DispatchQueue = ...
discovery.shutdown(queue: queue) { (error: Error?) in 
    print(error)
}

Configuration

You can configure the service discovery by passing a Configuration instance.

SwiftkubeServiceDiscovery supports the following configuration options:

• RetryStrategy: A retry strategy to control the reconnect behaviour for the underlying client in case of non-recoverable errors when serving service discovery subsriptions.

let strategy = RetryStrategy(
    policy: .maxAttemtps(20),
    backoff: .exponentiaBackoff(maxDelay: 60, multiplier: 2.0),
    initialDelay = 5.0,
    jitter = 0.2
)

let config = Configuration(retryStrategy: strategy)

let discovery = KubernetesServiceDiscovery(config: config)

Service lookup

To lookup Kubernetes "services" you have to pass an instance of LookupObject. You can specify the namespaces to search and provide a list of selectors to filter the desired objects.

SwiftkubeServiceDiscovery lookups return a list of KubernetesPods describing all of the matching pod objects that have an IP assigned.

let object = LookupObject(
    namespace: .allNamespaces,
    options: [
        .labelSelector(.exists(["app", "env"])),
        .labelSelector(.eq(["app": "nginx"])),
        .labelSelector(.notIn(["env": ["dev", "staging"]])),    
    ]
)

discovery.lookup(object) { result in
    switch result {
    case let .success(pods):
         pods.forEach { pod in
             print("\(pod.name), \(pod.namespace): \(pod.ip)")
         }
    case let .failure(error):
        // handle error
    }
}

Service subsription

You can subscribe to service lookups the same way, by providing a LookupObject:

let token = discovery.subscribe(to: object) { result in
    switch result {
    case let .success(pods):
        pods.forEach {
            print("\(pod.name), \(pod.namespace): \(pod.ip)")
        }
    case let .failure(error):
        print(error)
    }
} onComplete: { reason in
    print(reason)
}

token.cancel()

The client will try to reconnect to the API server according to the configured RetryStrategy and will serve updates until the subsription token is cancelled.

RBAC

TBD

Installation

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

.package(name: "SwiftkubeServiceDiscovery", url: "https://github.com/swiftkube/servicediscovery.git", from: "0.1.0"),

then include it as a dependency in your target:

import PackageDescription

let package = Package(
    // ...
    dependencies: [
        .package(name: "SwiftkubeServiceDiscovery", url: "https://github.com/swiftkube/servicediscovery.git", from: "0.1.0")
    ],
    targets: [
        .target(name: "<your-target>", dependencies: [
            .product(name: "SwiftkubeServiceDiscovery", package: "SwiftkubeServiceDiscovery"),
        ])
    ]
)

Then run swift build.

License

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