Hello World Sample for R (#1664)

* Helloworld R sample

* readme

* actually save the readme

* Update Docker and app

* Update readme release

* Update readme to match code

community/samples/serving/helloworld-r/.dockerignore

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+Dockerfile
+README.md
+*.pyc
+*.pyo
+*.pyd
+__pycache__

community/samples/serving/helloworld-r/Dockerfile

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+# Use the official Python image.
+# https://hub.docker.com/_/python
+FROM python:3.7
+
+# Copy local code to the container image.
+ENV APP_HOME /app
+WORKDIR $APP_HOME
+COPY . .
+
+# Install production dependencies.
+RUN pip install Flask gunicorn
+
+# Install R
+RUN apt-get update && \
+    apt-get install -y r-base
+
+# Run the web service on container startup. Here we use the gunicorn
+# webserver, with one worker process and 8 threads.
+# For environments with multiple CPU cores, increase the number of workers
+# to be equal to the cores available.
+CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 app:app

community/samples/serving/helloworld-r/HelloWorld.R

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+#!/usr/bin/Rscript
+TARGET <- Sys.getenv("TARGET", "World")
+
+message = paste("Hello ", TARGET, "!", sep = "")
+print(message)

community/samples/serving/helloworld-r/README.md

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+---
+title: "Hello World - R"
+linkTitle: "R"
+weight: 1
+type: "docs"
+---
+
+A simple web app that executes an R script. The R script reads an env
+variable `TARGET` and prints `Hello ${TARGET}!`. If the `TARGET` environment
+variable is not specified, the script uses `World`.
+
+Follow the steps below to create the sample code and then deploy the app to your
+cluster. You can also download a working copy of the sample, by running the
+following commands:
+
+```shell
+git clone -b "{{< branch >}}" https://github.com/knative/docs knative-docs
+cd knative-docs/docs/serving/samples/hello-world/helloworld-r
+```
+
+## Before you begin
+
+- A Kubernetes cluster with Knative installed. Follow the
+  [installation instructions](../../../../install/README.md) if you need to
+  create one.
+- [Docker](https://www.docker.com) installed and running on your local machine,
+  and a Docker Hub account configured (we'll use it for a container registry).
+
+## Recreating the sample code
+
+1. Create a new file named `HelloWorld.R` and paste the following script:
+
+   ```R
+   #!/usr/bin/Rscript
+   TARGET <- Sys.getenv("TARGET", "World")
+
+   message = paste("Hello ", TARGET, "!", sep = "")
+   print(message)
+   ```
+
+1. Create a new file named `app.py` and paste the following code. We use a
+   basic web server written in Python to execute the R script:
+
+   ```py
+   import os
+   import subprocess
+
+   from flask import Flask
+
+   app = Flask(__name__)
+
+   @app.route('/')
+   def hello_world():
+       try:
+           output = subprocess.check_output('/usr/bin/Rscript HelloWorld.R', shell=True)
+           print(output)
+       except subprocess.CalledProcessError:
+           return "Error in R script.", 500
+
+       return output
+
+
+   if __name__ == "__main__":
+       app.run(debug=True,host='0.0.0.0',port=int(os.environ.get('PORT', 8080)))
+   ```
+
+1. Create a new file named `Dockerfile` and copy the code block below into it.
+
+   ```docker
+   # Use the official Python image.
+   # https://hub.docker.com/_/python
+   FROM python:3.7
+
+   # Copy local code to the container image.
+   ENV APP_HOME /app
+   WORKDIR $APP_HOME
+   COPY . .
+
+   # Install production dependencies.
+   RUN pip install Flask gunicorn
+
+   # Install R
+   RUN apt-get update && \
+       apt-get install -y r-base
+
+   # Run the web service on container startup. Here we use the gunicorn
+   # webserver, with one worker process and 8 threads.
+   # For environments with multiple CPU cores, increase the number of workers
+   # to be equal to the cores available.
+   CMD exec gunicorn --bind :$PORT --workers 1 --threads 8 app:app
+   ```
+
+1. 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.
+
+   ```yaml
+   apiVersion: serving.knative.dev/v1alpha1
+   kind: Service
+   metadata:
+     name: helloworld-r
+     namespace: default
+   spec:
+     template:
+       spec:
+         containers:
+           - image: docker.io/{username}/helloworld-r
+             env:
+               - name: TARGET
+                 value: "R 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.
+
+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:
+
+   ```shell
+   # Build the container on your local machine
+   docker build -t {username}/helloworld-r .
+
+   # Push the container to docker registry
+   docker push {username}/helloworld-r
+   ```
+
+1. 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 using `kubectl`:
+
+   ```shell
+   kubectl apply --filename service.yaml
+   ```
+
+1. Now that your service is created, Knative performs 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).
+
+1. Run the following command to find the external IP address for your service.
+   The ingress IP for your cluster is returned. If you just created your
+   cluster, you might need to wait and rerun the command until your service gets
+   asssigned an external IP address.
+
+   ```shell
+   kubectl get svc knative-ingressgateway --namespace istio-system
+   ```
+
+   Example:
+
+   ```shell
+   NAME                     TYPE           CLUSTER-IP     EXTERNAL-IP      PORT(S)                                      AGE
+   knative-ingressgateway   LoadBalancer   10.23.247.74   35.203.155.229   80:32380/TCP,443:32390/TCP,32400:32400/TCP   2d
+
+   ```
+
+1. Run the following command to find the domain URL for your service:
+
+   ```shell
+   kubectl get ksvc helloworld-r  --output=custom-columns=NAME:.metadata.name,URL:.status.url
+   ```
+
+   Example:
+
+   ```shell
+   NAME                URL
+   helloworld-r    http://helloworld-r.default.example.com
+   ```
+
+1. Test your app by sending it a request. Use the following `curl` command with
+   the domain URL `helloworld-r.default.example.com` and `EXTERNAL-IP`
+   address that you retrieved in the previous steps:
+
+   ```shell
+   curl -H "Host: helloworld-r.default.example.com" http://{EXTERNAL_IP_ADDRESS}
+   ```
+
+   Example:
+
+   ```shell
+   curl -H "Host: helloworld-r.default.example.com" http://35.203.155.229
+   [1] "Hello R Sample v1!"
+   ```
+
+   > Note: Add `-v` option to get more detail if the `curl` command failed.
+
+## Removing the sample app deployment
+
+To remove the sample app from your cluster, delete the service record:
+
+```shell
+kubectl delete --filename service.yaml
+```

community/samples/serving/helloworld-r/app.py

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+import os
+import subprocess
+
+from flask import Flask
+
+app = Flask(__name__)
+
+@app.route('/')
+def hello_world():
+    try:
+        output = subprocess.check_output('/usr/bin/Rscript HelloWorld.R', shell=True)
+        print(output)
+    except subprocess.CalledProcessError:
+        return "Error in R script.", 500
+
+    return output
+
+
+if __name__ == "__main__":
+    app.run(debug=True,host='0.0.0.0',port=int(os.environ.get('PORT', 8080)))

community/samples/serving/helloworld-r/service.yaml

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+apiVersion: serving.knative.dev/v1alpha1
+kind: Service
+metadata:
+  name: helloworld-r
+  namespace: default
+spec:
+  template:
+    spec:
+      containers:
+      - image: docker.io/akitsch/helloworld-r
+        env:
+        - name: TARGET
+          value: "R Sample v1"