# Hello World - Ruby

This guide describes the steps required to create the `helloworld-ruby` sample app and deploy it to your cluster.

The sample app reads a `TARGET` environment variable, and prints `Hello ${TARGET}!`.
If `TARGET` is not specified, `World` is used as the default value.

You can also download a working copy of the sample, by running the
following commands:

```bash
git clone https://github.com/knative/docs.git knative-docs
cd knative-docs/code-samples/serving/hello-world/helloworld-ruby
```

## Prerequisites

- A Kubernetes cluster with Knative installed and DNS configured. See
  [Install Knative Serving](https://knative.dev/docs/install/serving/install-serving-with-yaml).
- [Docker](https://www.docker.com) installed and running on your local machine,
  and a Docker Hub account configured.
- (optional) The Knative CLI client [kn](https://github.com/knative/client/releases) that simplifies the deployment. Alternative you can also use [`kubectl`](https://kubernetes.io/docs/tasks/tools/install-kubectl/) and apply resource files directly.

## Recreating the sample code

1. Create a new directory and cd into it:

   ```bash
   mkdir app
   cd app
   ```

1. Create a file named `app.rb` and copy the following code block into it:

   ```ruby
   require 'sinatra'

   set :bind, '0.0.0.0'

   get '/' do
    target = ENV['TARGET'] || 'World'
    "Hello #{target}!\n"
   end
   ```

1. Create a file named `Dockerfile` and copy the following code block into it. See
   [official Ruby docker image](https://hub.docker.com/_/ruby/) for more
   details.

   ```docker
   # Use the official lightweight Ruby image.
   # https://hub.docker.com/_/ruby
   FROM ruby:2.6-slim

   # Install production dependencies.
   WORKDIR /usr/src/app
   COPY Gemfile Gemfile.lock ./
   ENV BUNDLE_FROZEN=true
   RUN gem install bundler && bundle install

   # Copy local code to the container image.
   COPY . ./

   # Run the web service on container startup.
   CMD ["ruby", "./app.rb"]
   ```

1. Create a file named `Gemfile` and copy the following text block into it.

   ```gem
   source 'https://rubygems.org'

   gem 'sinatra'
   gem 'rack', '>= 2.0.6'
   ```

1. Run bundle. If you don't have bundler installed, copy the
   [Gemfile.lock](Gemfile.lock) to your working directory.

   ```bash
   bundle install
   ```

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/v1
   kind: Service
   metadata:
     name: helloworld-ruby
     namespace: default
   spec:
     template:
       spec:
         containers:
           - image: docker.io/{username}/helloworld-ruby
             env:
               - name: TARGET
                 value: "Ruby Sample v1"
   ```

## Deploying

1. After the build has completed and the container is pushed to Docker Hub, you
   can deploy the app into your cluster.


=== "yaml"

       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/v1
       kind: Service
       metadata:
         name: helloworld-ruby
         namespace: default
       spec:
         template:
           spec:
             containers:
               - image: docker.io/{username}/helloworld-ruby
                 env:
                   - name: TARGET
                     value: "Ruby Sample v1"
          ```

       Ensure that the container image value
       in `service.yaml` matches the container you built in the previous step. Apply
       the configuration using `kubectl`:

       ```bash
       kubectl apply --filename service.yaml
       ```


=== "kn"

       With `kn` you can deploy the service with

       ```bash
       kn service create helloworld-ruby --image=docker.io/{username}/helloworld-ruby --env TARGET="Ruby Sample v1"
       ```

       This will wait until your service is deployed and ready, and ultimately it will print the URL through which you can access the service.

       The output will look like:

       ```
       Creating service 'helloworld-ruby' in namespace 'default':

        0.035s The Configuration is still working to reflect the latest desired specification.
        0.139s The Route is still working to reflect the latest desired specification.
        0.250s Configuration "helloworld-ruby" is waiting for a Revision to become ready.
        8.040s ...
        8.136s Ingress has not yet been reconciled.
        8.277s unsuccessfully observed a new generation
        8.398s Ready to serve.

      Service 'helloworld-ruby' created to latest revision 'helloworld-ruby-akhft-1' is available at URL:
      http://helloworld-ruby.default.1.2.3.4.sslip.io
      ```





   During the creation of your service, 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).

## Verification

1. Run one of the followings commands to find the domain URL for your service.


=== "kubectl"
       ```bash
       kubectl get ksvc helloworld-ruby  --output=custom-columns=NAME:.metadata.name,URL:.status.url
       ```

       Example:

       ```bash
       NAME                URL
       helloworld-ruby    http://helloworld-ruby.default.1.2.3.4.sslip.io
       ```


=== "kn"

       ```bash
       kn service describe helloworld-ruby -o url
       ```

       Example:

       ```bash
       http://helloworld-ruby.default.1.2.3.4.sslip.io
       ```




1. Now you can make a request to your app and see the result. Replace
   the following URL with the URL returned in the previous command.

   Example:

   ```bash
   curl http://helloworld-ruby.default.1.2.3.4.sslip.io
   Hello Ruby Sample v1!

   # Even easier with kn:
   curl $(kn service describe helloworld-ruby -o url)
   ```

   > Note: Add `-v` option to get more detail if the `curl` command failed.

## Removing

To remove the sample app from your cluster, delete the service record.


=== "kubectl"

      ```bash
      kubectl delete --filename service.yaml
      ```

=== "kn"

      ```bash
      kn service delete helloworld-ruby
      ```
