Hello World - Ruby

    Follow the steps below to create the sample code and then deploy the app to your cluster. 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 if you need to create one.
    • installed and running on your local machine, and a Docker Hub account configured (we’ll use it for a container registry).

    1. Create a new directory and cd into it:

      1. mkdir app
      2. cd app

    2. Create a file named app.rb and copy the code block below 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

    3. Create a file named Dockerfile and copy the code block below 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
      4. # Install production dependencies.
      5. WORKDIR /usr/src/app
      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"]

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

      1. 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.

      1. apiVersion: serving.knative.dev/v1
      2. kind: Service
      3. metadata:
      4.   name: helloworld-ruby
      5.   namespace: default
      6. spec:
      8.       containers:
      9.         - image: docker.io/{username}/helloworld-ruby
      10.           env:
      11.             - name: TARGET
      12.               value: "Ruby Sample v1"

    Once you have recreated the sample code files (or used the files in the sample folder) you’re ready to build and deploy the sample app.

    1. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing {username} with your Docker Hub username:

      1. # Build the container on your local machine
      2. docker build -t {username}/helloworld-ruby .
      4. # Push the container to docker registry
      5. docker push {username}/helloworld-ruby

    3. Now that your service is created, Knative will perform 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).

    4. To find the URL for your service, use

      1. kubectl get ksvc helloworld-ruby  --output=custom-columns=NAME:.metadata.name,URL:.status.url
      2. NAME                URL
      3. helloworld-ruby     http://helloworld-ruby.default.1.2.3.4.xip.io

    5. 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.

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

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

    1. kubectl delete --filename service.yaml