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 -b "main" 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.
  • 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 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 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 text block below 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.

  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:

kubectl apply --filename service.yaml

With kn you can deploy the service with

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

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

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)

    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 delete --filename service.yaml

kn service delete helloworld-ruby