Hello World - Ruby

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:

• A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions.
• 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 and apply resource files directly.

1. Create a new directory and cd into it:

   mkdir app
   cd app

2. Create a file named app.rb and copy the code block below 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 code block below 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 . ./
   # Run the web service on container startup.
   CMD ["ruby", "./app.rb"]

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

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

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"

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

• kn

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.

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 apply --filename service.yaml

With kn you can deploy the service with

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

• 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).

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

• kn

Example:

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

kn service describe helloworld-ruby -o url

Example:

http://helloworld-ruby.default.1.2.3.4.xip.io

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:

   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)

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

• kn