mirror of https://github.com/knative/docs.git
136 lines
4.4 KiB
Markdown
136 lines
4.4 KiB
Markdown
# Hello World - Scala using Akka HTTP sample
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A microservice which demonstrates how to get set up and running with Knative Serving when using [Scala](https://scala-lang.org/) and [Akka](https://akka.io/) [HTTP](https://doc.akka.io/docs/akka-http/current/). It will respond to a HTTP request with a text specified as an `ENV` variable named `MESSAGE`, defaulting to `"Hello World!"`.
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## Prerequisites
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* A Kubernetes cluster [installation](https://github.com/knative/docs/blob/master/install/README.md) with Knative Serving up and running.
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* [Docker](https://www.docker.com) installed locally, and running, optionally a Docker Hub account configured or some other Docker Repository installed locally.
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* [Java JDK8 or later](https://adoptopenjdk.net/installation.html) installed locally.
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* [Scala's](https://scala-lang.org/) standard build tool [sbt](https://www.scala-sbt.org/) installed locally.
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## Configuring the sbt build
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If you want to use your Docker Hub repository, set the repository to "docker.io/yourusername/yourreponame".
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If you use Minikube, you first need to run:
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```shell
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eval $(minikube docker-env)
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```
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If want to use the Docker Repository inside Minikube, either set this to "dev.local" or if you want to use another repository name, then you need to run the following command after `docker:publishLocal`:
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```shell
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docker tag yourreponame/helloworld-scala:<version> dev.local/helloworld-scala:<version>
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```
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Otherwise Knative Serving won't be able to resolve this image from the Minikube Docker Repository.
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You specify the repository in [build.sbt](build.sbt):
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```scala
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dockerRepository := Some("your_repository_name")
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```
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You can learn more about the build configuration syntax [here](https://www.scala-sbt.org/1.x/docs/Basic-Def.html).
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## Configuring the Service descriptor
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Importantly, in [helloworld-scala.yaml](helloworld-scala.yaml) **change the image reference to match up with the repository**, name, and version specified in the [build.sbt](build.sbt) in the previous section.
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```yaml
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apiVersion: serving.knative.dev/v1alpha1
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kind: Service
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metadata:
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name: helloworld-scala
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namespace: default
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spec:
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runLatest:
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configuration:
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revisionTemplate:
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spec:
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container:
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image: "your_repository_name/helloworld-scala:0.0.1"
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imagePullPolicy: IfNotPresent
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env:
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- name: MESSAGE
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value: "Scala & Akka on Knative says hello!"
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- name: HOST
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value: "localhost"
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```
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## Publishing to Docker
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In order to build the project and create and push the Docker image, run either:
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```shell
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sbt docker:publishLocal
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```
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or
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```shell
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sbt docker:publish
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```
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Which of them to use is depending on whether you are publishing to a remote or a local Docker Repository.
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## Deploying to Knative Serving
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Locate the Knative Serving gateway address:
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```shell
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# In Knative 0.2.x and prior versions, `knative-ingressgateway` service was used instead of `istio-ingressgateway`.
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kubectl get svc istio-ingressgateway --namespace istio-system
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```
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Example output, see the address under **EXTERNAL-IP**:
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```shell
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NAME TYPE CLUSTER-IP EXTERNAL-IP PORTS) AGE
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xxxxxxx-ingressgateway LoadBalancer 123.456.789.01 111.111.111.111 80:32380/TCP,443:32390/TCP,32400:32400/TCP 1m
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```
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Then export the external address obtained for ease of reuse later:
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```shell
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export SERVING_GATEWAY=<replace this with the address obtained>
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```
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If you use Minikube, then you will likely have to do the following instead:
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```shell
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export SERVING_GATEWAY=$(minikube ip):$(kubectl get svc istio-ingressgateway --namespace istio-system --output 'jsonpath={.spec.ports[?(@.port==80)].nodePort}')
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```
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Apply the [Service yaml definition](helloworld-scala.yaml):
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```shell
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kubectl apply --filename helloworld-scala.yaml
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```
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Then find the service host:
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```shell
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kubectl get ksvc helloworld-scala \
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--output=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain
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# It will print something like this, the DOMAIN is what you're going to use as HTTP Host header:
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# NAME DOMAIN
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# helloworld-scala helloworld-scala.default.example.com
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```
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Finally, to try your service, use the obtained address in the Host header:
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```shell
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curl -v -H "Host: helloworld-scala.default.example.com" http://$SERVING_GATEWAY
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```
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## Cleanup
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```shell
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kubetl delete --filename helloworld-scala.yaml
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``` |