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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.
-
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") ] )
-
Add the web server code to a file named
main.swift
in aSources/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() }
-
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"]
-
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.
-
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
-
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 thekubectl
command:kubectl apply --filename service.yaml
-
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).
-
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
-
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
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