docs/code-samples/serving/hello-world/helloworld-ruby

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:

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.
• Docker installed and running on your local machine, and a Docker Hub account configured.
• (optional) The Knative CLI client kn that simplifies the deployment. Alternative you can also use kubectl and apply resource files directly.

Recreating the sample code

1. Create a new directory and cd into it:

   mkdir app
   cd app
   

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

   require 'sinatra'
   
   set :bind, '0.0.0.0'
   
   get '/' do
    target = ENV['TARGET'] || 'World'
    "Hello #{target}!\n"
   end
   

3. Create a file named Dockerfile and copy the following code block into it. See official Ruby docker image for more details.

   # 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"]
   

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

   source 'https://rubygems.org'
   
   gem 'sinatra'
   gem 'rack', '>= 2.0.6'
   

5. Run bundle. If you don't have bundler installed, copy the Gemfile.lock to your working directory.

   bundle install
   

6. 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.

   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:

   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
  ```