mirror of https://github.com/knative/docs.git
164 lines
4.6 KiB
Markdown
164 lines
4.6 KiB
Markdown
# Hello World - R server
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A simple web app created with R package, [plumber](https://www.rplumber.io).
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plumber creates a REST API by adding annotations to your R code. The R script
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reads an environment variable `TARGET` and prints `Hello ${TARGET}!`. If the
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`TARGET` environment variable is not specified, the script uses `World`.
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Follow the steps below to create the sample code and then deploy the app to your
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cluster. You can also download a working copy of the sample, by running the
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following commands:
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```bash
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git clone https://github.com/knative/docs.git knative-docs
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cd knative-docs/code-samples/community/serving/hello-world/helloworld-r
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```
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## Before you begin
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- A Kubernetes cluster with Knative installed. Follow the
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[Knative installation instructions](https://knative.dev/docs/install/) if you need to
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create 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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## Recreating the sample code
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1. Create a new file named `HelloWorld.R` and paste the following script:
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```R
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#' HelloWorld function
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#' @get /
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#' @html
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function() {
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TARGET <- Sys.getenv("TARGET", "World")
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message = paste("Hello ", TARGET, "!", sep = "")
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print(message)
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}
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```
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This file defines the endpoint `/`, using plumber annotations.
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1. Create a new file named `server.R` and paste the following code:
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```R
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library(plumber) # https://www.rplumber.io/
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# Translate the HelloWorld file into a Plumber API
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r <- plumb("HelloWorld.R")
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# Get the PORT env var
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PORT <- strtoi(Sys.getenv("PORT", 8080))
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# Run the API
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r$run(port=PORT, host="0.0.0.0")
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```
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1. Create a new file named `Dockerfile` and paste the following code:
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```docker
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# The official R base image
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# https://hub.docker.com/_/r-base
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FROM r-base:3.6.0
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# Copy local code to the container image.
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WORKDIR /usr/src/app
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COPY . .
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# Install R packages
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RUN Rscript -e "install.packages('plumber', repos='http://cran.us.r-project.org/')"
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# Run the web service on container startup.
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CMD ["Rscript", "server.R"]
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```
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1. 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-rserver
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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-rserver
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env:
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- name: TARGET
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value: "R Server 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-rserver .
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# Push the container to docker registry
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docker push {username}/helloworld-rserver
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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 performs 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. Run the following command to find the domain URL for your service:
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```bash
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kubectl get ksvc helloworld-r --output=custom-columns=NAME:.metadata.name,URL:.status.url
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```
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Example:
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```bash
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NAME URL
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helloworld-r http://helloworld-r.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-rserver.default.1.2.3.4.sslip.io
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```
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Example:
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```bash
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curl http://helloworld-rserver.default.1.2.3.4.sslip.io
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[1] "Hello R Sample v1!"
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```
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> Note: Add `-v` option to get more detail if the `curl` command failed.
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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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