mirror of https://github.com/knative/docs.git
156 lines
4.8 KiB
Markdown
156 lines
4.8 KiB
Markdown
# Hello World - Dart
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A simple web app written in the [Dart](https://www.dart.dev) programming language
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that you can use for testing. It reads in the env variable `TARGET` and prints
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`"Hello $TARGET"`. If `TARGET` is not specified, it will use `"World"` as
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`TARGET`.
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## Prerequisites
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- A Kubernetes cluster with Knative installed and DNS configured. Follow the
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[Knative installation instructions](https://knative.dev/docs/install/) if you need to create
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one.
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- [Docker](https://www.docker.com) installed and running on your local machine,
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and a Docker Hub account configured (we'll use it for a container registry).
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- [dart-sdk](https://www.dart.dev/tools/sdk#install) installed and
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configured if you want to run the program locally.
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## Recreating the sample code
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While you can clone all of the code from this directory, it is useful to know
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how to build a hello world Dart application step-by-step. This application can
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be created using the following instructions.
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1. Create a new directory and write `pubspec.yaml` as follows:
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```yaml
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name: hello_world_dart
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publish_to: none # let's not accidentally publish this to pub.dartlang.org
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environment:
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sdk: ">=2.12.0 <3.0.0"
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dependencies:
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shelf: ^1.0.0
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```
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2. If you want to run locally, install dependencies. If you only want to run in
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Docker or Knative, you can skip this step.
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```bash
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> pub get
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```
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3. Create a new file `bin/server.dart` and write the following code:
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```dart
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import 'dart:io';
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import 'package:shelf/shelf.dart';
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import 'package:shelf/shelf_io.dart';
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Future main() async {
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// Find port to listen on from environment variable.
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final port = int.parse(Platform.environment['PORT'] ?? '8080');
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// Read $TARGET from environment variable.
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final target = Platform.environment['TARGET'] ?? 'World';
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Response handler(Request request) => Response.ok('Hello $target');
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// Serve handler on given port.
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final server = await serve(
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const Pipeline().addMiddleware(logRequests()).addHandler(handler),
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InternetAddress.anyIPv4,
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port,
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);
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print('Serving at http://${server.address.host}:${server.port}');
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}
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```
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4. Create a new file named `Dockerfile`, this file defines instructions for
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dockerizing your applications, for dart apps this can be done as follows:
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```Dockerfile
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# Use Google's official Dart image.
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# https://hub.docker.com/r/google/dart-runtime/
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FROM google/dart-runtime
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```
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5. Create a new file, `service.yaml` and copy the following service definition
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into the file. Make sure to replace `{username}` with your Docker Hub
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username.
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```yaml
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apiVersion: serving.knative.dev/v1
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kind: Service
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metadata:
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name: helloworld-dart
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namespace: default
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spec:
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template:
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spec:
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containers:
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- image: docker.io/{username}/helloworld-dart
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env:
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- name: TARGET
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value: "Dart Sample v1"
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```
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## Building and deploying the sample
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Once you have recreated the sample code files (or used the files in the sample
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folder) you're ready to build and deploy the sample app.
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1. Use Docker to build the sample code into a container. To build and push with
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Docker Hub, run these commands replacing `{username}` with your Docker Hub
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username:
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```bash
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# Build the container on your local machine
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docker build -t {username}/helloworld-dart .
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# Push the container to docker registry
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docker push {username}/helloworld-dart
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```
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1. After the build has completed and the container is pushed to docker hub, you
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can deploy the app into your cluster. Ensure that the container image value
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in `service.yaml` matches the container you built in the previous step. Apply
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the configuration using `kubectl`:
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```bash
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kubectl apply --filename service.yaml
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```
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1. Now that your service is created, Knative will perform the following steps:
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- Create a new immutable revision for this version of the app.
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- Network programming to create a route, ingress, service, and load balance
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for your app.
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- Automatically scale your pods up and down (including to zero active pods).
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1. To find the URL for your service, use
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```
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kubectl get ksvc helloworld-dart --output=custom-columns=NAME:.metadata.name,URL:.status.url
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NAME URL
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helloworld-dart http://helloworld-dart.default.1.2.3.4.sslip.io
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```
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1. Now you can make a request to your app and see the result. Replace
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the URL below with the URL returned in the previous command.
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```bash
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curl http://helloworld-dart.default.1.2.3.4.sslip.io
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Hello Dart Sample v1
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```
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## Removing the sample app deployment
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To remove the sample app from your cluster, delete the service record:
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```bash
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kubectl delete --filename service.yaml
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```
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