Hello World - Swift

A simple web app written in Swift that you can use for testing. The app reads in an env variable TARGET and prints “Hello ${TARGET}!”. If TARGET is not specified, the app uses “World” as the TARGET.

Prerequisites

  • You must have a Kubernetes cluster with Knative installed and DNS configured. If you need to create a cluster, follow the installation instructions.
  • You must have Docker installed and running on your local machine, and a Docker Hub account configured (used for container registry).

Recreating the sample code

While you can clone all of the code from this directory, it might be more useful if you build this app step-by-step. The following instructions recreate the source files from this folder.

  1. Create a the Package.swift to declare your package and its dependencies. This app uses Swifter, a tiny http server engine for Swift.

     // swift-tools-version:4.0

 import PackageDescription

 let package = Package(
     name: "HelloSwift",
     dependencies: [
         .package(url: "https://github.com/httpswift/swifter.git", .upToNextMajor(from: "1.4.5"))
     ],
     targets: [
         .target(
         name: "HelloSwift",
         dependencies: ["Swifter"],
         path: "./Sources")
     ]
 )

  2. Add the web server code to a file named main.swift in a Sources/HelloSwift/ folder:

     import Swifter
 import Dispatch
 import Foundation

 let server = HttpServer()
 server["/"] = { r in
     let target = ProcessInfo.processInfo.environment["TARGET"] ?? "World"
     return HttpResponse.ok(.html("Hello \(target)"))
 }

 let semaphore = DispatchSemaphore(value: 0)
 do {
     let port = UInt16(ProcessInfo.processInfo.environment["PORT"] ?? "8080")
     try server.start(port!, forceIPv4: true)
     print("Server has started ( port = \(try server.port()) ). Try to connect now...")
     semaphore.wait()
 } catch {
     print("Server start error: \(error)")
     semaphore.signal()
 }

  3. In your project directory, create a file named Dockerfile and copy the code block below into it.

     # Use the official Swift image.
 # https://hub.docker.com/_/swift
 FROM swift:4.2

 # Copy local code to the container image.
 WORKDIR /app
 COPY . .

 # Install dependencies and build.
 RUN swift build -c release

 # Run the web service on container startup.
 CMD [ ".build/release/HelloSwift"]

  4. Create a new file, service.yaml, and copy the following service definition into the file. Replace {username} with your Docker Hub username.

    apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld-swift
  namespace: default
spec:
  template:
    spec:
    containers:
      - image: docker.io/{username}/helloworld-swift
        env:
          - name: TARGET
        value: "Swift"

Building and deploying the sample

Once you have recreated the sample code files (or used the files in the sample folder) you’re ready to build and deploy the sample app.

  1. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands, replacing {username} with your Docker Hub username:

    # Build the container on your local machine
docker build -t {username}/helloworld-swift .

# Push the container to docker registry
docker push {username}/helloworld-swift

  2. After the build has completed and the container is pushed to Docker Hub, you can deploy the app into your cluster. Ensure that the container image value in the service.yaml file matches the container you built in the previous step. Apply the configuration using the kubectl command:

    kubectl apply --filename service.yaml

  3. Now that your service is created, Knative performs the following steps:

    • Creates a new immutable revision for this version of the app.
    • Network programming to create a route, ingress, service, and load balancing for your app.
    • Automatically scales your pods up and down (including to zero active pods).

  4. To find the URL for your service, use the following command:

    kubectl get ksvc helloworld-swift  --output=custom-columns=NAME:.metadata.name,URL:.status.url
NAME               URL
helloworld-swift   http://helloworld-swift.default.1.2.3.4.xip.io

  5. Now you can make a request to your app and see the result. Replace the URL below with the URL returned in the previous command.

    curl http://helloworld-swift.default.1.2.3.4.xip.io
Hello Swift

Removing the sample app deployment

To remove the sample app from your cluster, delete the service record:

kubectl delete --filename service.yaml