|
| 1 | +--- |
| 2 | +title: "Hello World - R server" |
| 3 | +linkTitle: "R server" |
| 4 | +weight: 1 |
| 5 | +type: "docs" |
| 6 | +--- |
| 7 | + |
| 8 | +A simple web app created with R package, [plumber](https://www.rplumber.io). |
| 9 | +plumber creates a REST API by adding annotations to your R code. The R script |
| 10 | +reads an environment variable `TARGET` and prints `Hello ${TARGET}!`. If the |
| 11 | +`TARGET` environment variable is not specified, the script uses `World`. |
| 12 | + |
| 13 | +Follow the steps below to create the sample code and then deploy the app to your |
| 14 | +cluster. You can also download a working copy of the sample, by running the |
| 15 | +following commands: |
| 16 | + |
| 17 | +```shell |
| 18 | +git clone -b "{{< branch >}}" https://github.com/knative/docs knative-docs |
| 19 | +cd knative-docs/docs/serving/samples/hello-world/helloworld-r |
| 20 | +``` |
| 21 | + |
| 22 | +## Before you begin |
| 23 | + |
| 24 | +- A Kubernetes cluster with Knative installed. Follow the |
| 25 | + [installation instructions](../../../../install/README.md) if you need to |
| 26 | + create one. |
| 27 | +- [Docker](https://www.docker.com) installed and running on your local machine, |
| 28 | + and a Docker Hub account configured (we'll use it for a container registry). |
| 29 | + |
| 30 | +## Recreating the sample code |
| 31 | + |
| 32 | +1. Create a new file named `HelloWorld.R` and paste the following script: |
| 33 | + |
| 34 | + ```R |
| 35 | + #' HelloWorld function |
| 36 | + #' @get / |
| 37 | + #' @html |
| 38 | + function() { |
| 39 | + TARGET <- Sys.getenv("TARGET", "World") |
| 40 | + |
| 41 | + message = paste("Hello ", TARGET, "!", sep = "") |
| 42 | + print(message) |
| 43 | + } |
| 44 | + ``` |
| 45 | + |
| 46 | + This file defines the endpoint `/`, using plumber annotations. |
| 47 | + |
| 48 | + 1. Create a new file named `server.R` and paste the following code: |
| 49 | + |
| 50 | + ```R |
| 51 | + library(plumber) # https://www.rplumber.io/ |
| 52 | + |
| 53 | + # Translate the HelloWorld file into a Plumber API |
| 54 | + r <- plumb("HelloWorld.R") |
| 55 | + # Get the PORT env var |
| 56 | + PORT <- strtoi(Sys.getenv("PORT", 8080)) |
| 57 | + # Run the API |
| 58 | + r$run(port=PORT, host="0.0.0.0") |
| 59 | + ``` |
| 60 | + |
| 61 | + 1. Create a new file named `Dockerfile` and paste the following code: |
| 62 | + |
| 63 | + ```docker |
| 64 | + # The official R base image |
| 65 | + # https://hub.docker.com/_/r-base |
| 66 | + FROM r-base:3.6.0 |
| 67 | + |
| 68 | + # Copy local code to the container image. |
| 69 | + WORKDIR /usr/src/app |
| 70 | + COPY . . |
| 71 | + |
| 72 | + # Install R packages |
| 73 | + RUN Rscript -e "install.packages('plumber', repos='http://cran.us.r-project.org/')" |
| 74 | + |
| 75 | + # Run the web service on container startup. |
| 76 | + CMD ["Rscript", "server.R"] |
| 77 | + ``` |
| 78 | + |
| 79 | + |
| 80 | +1. Create a new file, `service.yaml` and copy the following service definition |
| 81 | + into the file. Make sure to replace `{username}` with your Docker Hub |
| 82 | + username. |
| 83 | + |
| 84 | + ```yaml |
| 85 | + apiVersion: serving.knative.dev/v1alpha1 |
| 86 | + kind: Service |
| 87 | + metadata: |
| 88 | + name: helloworld-rserver |
| 89 | + namespace: default |
| 90 | + spec: |
| 91 | + template: |
| 92 | + spec: |
| 93 | + containers: |
| 94 | + - image: docker.io/{username}/helloworld-rserver |
| 95 | + env: |
| 96 | + - name: TARGET |
| 97 | + value: "R Server Sample v1" |
| 98 | + ``` |
| 99 | + |
| 100 | +## Building and deploying the sample |
| 101 | + |
| 102 | +Once you have recreated the sample code files (or used the files in the sample |
| 103 | +folder) you're ready to build and deploy the sample app. |
| 104 | + |
| 105 | +1. Use Docker to build the sample code into a container. To build and push with |
| 106 | + Docker Hub, run these commands replacing `{username}` with your Docker Hub |
| 107 | + username: |
| 108 | + |
| 109 | + ```shell |
| 110 | + # Build the container on your local machine |
| 111 | + docker build -t {username}/helloworld-rserver . |
| 112 | + |
| 113 | + # Push the container to docker registry |
| 114 | + docker push {username}/helloworld-rserver |
| 115 | + ``` |
| 116 | + |
| 117 | +1. After the build has completed and the container is pushed to docker hub, you |
| 118 | + can deploy the app into your cluster. Ensure that the container image value |
| 119 | + in `service.yaml` matches the container you built in the previous step. Apply |
| 120 | + the configuration using `kubectl`: |
| 121 | + |
| 122 | + ```shell |
| 123 | + kubectl apply --filename service.yaml |
| 124 | + ``` |
| 125 | + |
| 126 | +1. Now that your service is created, Knative performs the following steps: |
| 127 | + |
| 128 | + - Create a new immutable revision for this version of the app. |
| 129 | + - Network programming to create a route, ingress, service, and load balance |
| 130 | + for your app. |
| 131 | + - Automatically scale your pods up and down (including to zero active pods). |
| 132 | + |
| 133 | +1. Run the following command to find the external IP address for your service. |
| 134 | + The ingress IP for your cluster is returned. If you just created your |
| 135 | + cluster, you might need to wait and rerun the command until your service gets |
| 136 | + asssigned an external IP address. |
| 137 | + |
| 138 | + ```shell |
| 139 | + kubectl get svc knative-ingressgateway --namespace istio-system |
| 140 | + ``` |
| 141 | + |
| 142 | + Example: |
| 143 | + |
| 144 | + ```shell |
| 145 | + NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE |
| 146 | + knative-ingressgateway LoadBalancer 10.23.247.74 35.203.155.229 80:32380/TCP,443:32390/TCP,32400:32400/TCP 2d |
| 147 | + |
| 148 | + ``` |
| 149 | + |
| 150 | +1. Run the following command to find the domain URL for your service: |
| 151 | + |
| 152 | + ```shell |
| 153 | + kubectl get ksvc helloworld-r --output=custom-columns=NAME:.metadata.name,URL:.status.url |
| 154 | + ``` |
| 155 | + |
| 156 | + Example: |
| 157 | + |
| 158 | + ```shell |
| 159 | + NAME URL |
| 160 | + helloworld-r http://helloworld-r.default.example.com |
| 161 | + ``` |
| 162 | + |
| 163 | +1. Test your app by sending it a request. Use the following `curl` command with |
| 164 | + the domain URL `helloworld-rserver.default.example.com` and `EXTERNAL-IP` |
| 165 | + address that you retrieved in the previous steps: |
| 166 | + |
| 167 | + ```shell |
| 168 | + curl -H "Host: helloworld-rserver.default.example.com" http://{EXTERNAL_IP_ADDRESS} |
| 169 | + ``` |
| 170 | + |
| 171 | + Example: |
| 172 | + |
| 173 | + ```shell |
| 174 | + curl -H "Host: helloworld-rserver.default.example.com" http://35.203.155.229 |
| 175 | + [1] "Hello R Sample v1!" |
| 176 | + ``` |
| 177 | + |
| 178 | + > Note: Add `-v` option to get more detail if the `curl` command failed. |
| 179 | +
|
| 180 | +## Removing the sample app deployment |
| 181 | + |
| 182 | +To remove the sample app from your cluster, delete the service record: |
| 183 | + |
| 184 | +```shell |
| 185 | +kubectl delete --filename service.yaml |
| 186 | +``` |
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