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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 "master" 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
-
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'] || 'World' "Hello #{target}!\n" end
-
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"]
-
Create a file named
Gemfile
and copy the text block below into it.source 'https://rubygems.org' gem 'sinatra' gem 'rack', '>= 2.0.6'
-
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/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
- After the build has completed and the container is pushed to Docker Hub, you can deploy the app into your cluster.
-
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
- 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
-
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 thecurl
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
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