---
title: "Hello World - Ruby"
linkTitle: "Ruby"
weight: 1
type: "docs"
---

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:

```shell
git clone -b "{{< branch >}}" https://github.com/knative/docs knative-docs
cd knative-docs/docs/serving/samples/hello-world/helloworld-ruby
```

## Prerequisites

- A Kubernetes cluster with Knative installed and DNS configured. Follow the
  [installation instructions](../../../../install/README.md).
- [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:

   ```shell
   mkdir app
   cd app
   ```

1. Create a file named `app.rb` and copy the code block below 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 code block below 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 text block below 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.

   ```shell
   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.

{{< tabs name="helloworld_ruby" default="kn" >}}
{{% tab name="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`:

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

   {{< /tab >}}
   {{% tab name="kn" %}}

   With `kn` you can deploy the service with

   ```shell
   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.xip.io
  ```

{{< /tab >}}
{{< /tabs >}}

   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.

{{< tabs name="service_url" default="kn" >}}
{{% tab name="kubectl" %}}
   ```shell
   kubectl get ksvc helloworld-ruby  --output=custom-columns=NAME:.metadata.name,URL:.status.url
   ```

   Example:

   ```shell
   NAME                URL
   helloworld-ruby    http://helloworld-ruby.default.1.2.3.4.xip.io
   ```

{{< /tab >}}
{{% tab name="kn" %}}

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

   Example:

   ```shell
   http://helloworld-ruby.default.1.2.3.4.xip.io
   ```
   {{< /tab >}}
   {{< /tabs >}}

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

   Example:

   ```shell
   curl http://helloworld-ruby.default.1.2.3.4.xip.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.

{{< tabs name="service_url" default="kn" >}}
{{% tab name="kubectl" %}}

  ```shell
  kubectl delete --filename service.yaml
  ```
{{< /tab >}}
{{% tab name="kn" %}}

  ```shell
  kn service delete helloworld-ruby
  ```

{{< /tab >}}
{{< /tabs >}}