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Hello World - Dart
A simple web app written in the Dart programming language
that you can use for testing. It reads in the env variable TARGET
and prints
"Hello $TARGET"
. If TARGET
is not specified, it will use "World"
as
TARGET
.
Prerequisites
- A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions if you need to create one.
- Docker installed and running on your local machine, and a Docker Hub account configured (we’ll use it for a container registry).
- dart-sdk installed and configured if you want to run the program locally.
Recreating the sample code
While you can clone all of the code from this directory, it is useful to know how to build a hello world Dart application step-by-step. This application can be created using the following instructions.
-
Create a new directory and write
pubspec.yaml
as follows:name: hello_world_dart publish_to: none # let's not accidentally publish this to pub.dartlang.org description: Hello world server example in Dart environment: sdk: ">=2.1.0 <3.0.0" dependencies: shelf: ^0.7.3
-
If you want to run locally, install dependencies. If you only want to run in Docker or Knative, you can skip this step.
> pub get
-
Create a new file
bin/server.dart
and write the following code:import 'dart:io'; import 'package:shelf/shelf.dart'; import 'package:shelf/shelf_io.dart'; Future main() async { // Find port to listen on from environment variable. var port = int.tryParse(Platform.environment['PORT'] ?? '8080'); // Read $TARGET from environment variable. var target = Platform.environment['TARGET'] ?? 'World'; Response handler(Request request) => Response.ok('Hello $target'); // Serve handler on given port. var server = await serve( Pipeline().addMiddleware(logRequests()).addHandler(handler), InternetAddress.anyIPv4, port, ); print('Serving at http://${server.address.host}:${server.port}'); }
-
Create a new file named
Dockerfile
, this file defines instructions for dockerizing your applications, for dart apps this can be done as follows:# Use Google's official Dart image. # https://hub.docker.com/r/google/dart-runtime/ FROM google/dart-runtime
-
Create a new file,
service.yaml
and copy the following service definition into the file. Make sure to replace{username}
with your Docker Hub username.apiVersion: serving.knative.dev/v1 kind: Service metadata: name: helloworld-dart namespace: default spec: template: spec: containers: - image: docker.io/{username}/helloworld-dart env: - name: TARGET value: "Dart Sample v1"
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-dart . # Push the container to docker registry docker push {username}/helloworld-dart
-
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
service.yaml
matches the container you built in the previous step. Apply the configuration usingkubectl
:kubectl apply --filename service.yaml
-
Now that your service is created, Knative will perform the following steps:
- Create a new immutable revision for this version of the app.
- Network programming to create a route, ingress, service, and load balance for your app.
- Automatically scale your pods up and down (including to zero active pods).
-
To find the URL for your service, use
kubectl get ksvc helloworld-dart --output=custom-columns=NAME:.metadata.name,URL:.status.url NAME URL helloworld-dart http://helloworld-dart.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-dart.default.1.2.3.4.xip.io Hello Dart Sample v1
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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