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Hello World - Ruby sample

A simple wenb app written in Ruby that you can use for testing. It reads in an env variable TARGET and prints "Hello World: ${TARGET}!". If TARGET is not specified, it will use "NOT SPECIFIED" as the TARGET.

Prerequisites

A Kubernetes cluster with Knative installed. Follow the installation instructions if you need to create one.
Docker installed and running on your local machine, and a Docker Hub account configured (we'll use it for a container registry).

Steps to recreate the sample code

While you can clone all of the code from this directory, hello world apps are generally more useful if you build them step-by-step. The following instructions recreate the source files from this folder.

Create a new directory and cd into it:
```
mkdir app
cd app
```

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'] || 'NOT SPECIFIED'
  "Hello World: #{target}!\n"
end

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

FROM ruby

RUN bundle config --global frozen 1

WORKDIR /usr/src/app
COPY Gemfile Gemfile.lock ./
RUN bundle install

COPY . .

ENV PORT 8080
EXPOSE 8080

CMD ["ruby", "./app.rb"]

Create a file named Gemfile and copy the text block below into it.
```
source 'https://rubygems.org'

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

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/v1alpha1
kind: Service
metadata:
  name: helloworld-ruby
  namespace: default
spec:
  runLatest:
    configuration:
      revisionTemplate:
        spec:
          container:
            image: docker.io/{username}/helloworld-ruby
            env:
            - name: TARGET
              value: "Ruby Sample v1"

Build and deploy this sample

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.

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:

# Build the container on your local machine
docker build -t {username}/helloworld-ruby .

# Push the container to docker registry
docker push {username}/helloworld-ruby

After the build has completed and the container is pushed to docker hub, you can deploy the app into your cluster. 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 -f service.yaml
```
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).

To find the URL and IP address for your service, use kubectl to list the ingress points in the cluster:

kubectl get ing

NAME                        HOSTS                                                                                   ADDRESS        PORTS     AGE
helloworld-ruby-ingress   helloworld-ruby.default.demo-domain.com,*.helloworld-ruby.default.demo-domain.com   35.232.134.1   80        1m

Now you can make a request to your app to see the result. Replace {IP_ADDRESS} with the address you see returned in the previous step.
```
curl -H "Host: helloworld-ruby.default.demo-domain.com" http://{IP_ADDRESS}
Hello World: Ruby Sample v1!
```

Remove the sample app deployment

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

kubectl delete -f service.yaml

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