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:
    1. mkdir app
    2. cd app
    1. Create a file named app.rb and copy the following code block into it:
    1. require 'sinatra'
    3. set :bind, '0.0.0.0'
    5. get '/' do
    6.  target = ENV['TARGET'] || 'World'
    7.  "Hello #{target}!\n"
    8. end
    1. Create a file named Dockerfile and copy the following code block into it. See official Ruby docker image for more details.
    1. # Use the official lightweight Ruby image.
    2. # https://hub.docker.com/_/ruby
    3. FROM ruby:2.6-slim
    5. # Install production dependencies.
    6. COPY Gemfile Gemfile.lock ./
    7. ENV BUNDLE_FROZEN=true
    8. RUN gem install bundler && bundle install
    10. # Copy local code to the container image.
    11. COPY . ./
    13. # Run the web service on container startup.
    14. CMD ["ruby", "./app.rb"]
    1. Create a file named Gemfile and copy the following text block into it.
    1. source 'https://rubygems.org'
    3. gem 'sinatra'
    4. gem 'rack', '>= 2.0.6'
    1. Run bundle. If you don’t have bundler installed, copy the to your working directory.
    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.
    1. apiVersion: serving.knative.dev/v1
    2. kind: Service
    3. metadata:
    4.   name: helloworld-ruby
    5.   namespace: default
    6. spec:
    7.   template:
    8.     spec:
    9.       containers:
    10.         - image: docker.io/{username}/helloworld-ruby
    11.             - name: TARGET
    12.               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.

    yaml

    1. Create a new file, 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:

    1. kubectl apply --filename service.yaml

    With kn you can deploy the service with

    1. 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’:

    1. 0.035s The Configuration is still working to reflect the latest desired specification.
    2. 0.139s The Route is still working to reflect the latest desired specification.
    3. 0.250s Configuration "helloworld-ruby" is waiting for a Revision to become ready.
    4. 8.040s ...
    5. 8.136s Ingress has not yet been reconciled.
    6. 8.277s unsuccessfully observed a new generation
    7. 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).
    1. Run one of the followings commands to find the domain URL for your service.

    kubectl

    1. NAME                URL
    2. helloworld-ruby    http://helloworld-ruby.default.1.2.3.4.sslip.io

    kn

    1. kn service describe helloworld-ruby -o url

    Example:

    1. 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:

    1. curl http://helloworld-ruby.default.1.2.3.4.sslip.io
    2. Hello Ruby Sample v1!
    4. # Even easier with kn:

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

    kubectl

    kn

    1. kn service delete helloworld-ruby