Developing with Kuby

Kuby used to ship with a default environment called "development" that was capable of running your application locally using the copy of Kubernetes that comes with Docker Desktop.

Unfortunately it proved to be too difficult to maintain, so support was removed in version 0.12.0.

Testing with Kind

While Kuby doesn't support developing your application inside Kubernetes, it does support deploying it to a local Kubernetes cluster for testing purposes using Kind.

Kind is a tool that can easily create ephemeral Kubernetes clusters on-the-fly. The kuby-kind gem features a Kuby provider that makes it a snap to deploy to a local cluster.

Configuring the Kind Provider

1. First, add the kuby-kind gem to your Gemfile and run bundle install.

2. Create a development environment and configure Kind as the provider.

   require 'kuby/kind'
   
   Kuby.define('my-app') do
     environment(:development) do
       kubernetes do
         provider :kind
       end
     end
   end

3. Run setup

   bundle exec kuby -e development setup

4. Deploy

   bundle exec kuby -e development deploy

Sharing Configuration Between Environments

To keep the code focused, the docker do ... end section was omitted from the example above. Let's look at a more complete example.

We could duplicate configuration from the production environment, but it would be nice if we could share it instead. Configuration sharing can be done with Ruby lambas and instance_exec. For example:

Kuby.define('my-app') do
  shared = -> do
    docker do
      image_url 'registry.gitlab.com/username/repo'

      credentials do
        # ...
      end
    end
  end

  environment(:production) do
    instance_exec(&shared)

    kubernetes do
      # production provider
      provider :linode do
        # ...
      end

      add_plugin :rails_app do
        hostname 'myapp.com'
      end
    end
  end

  environment(:development) do
    instance_exec(&shared)

    kubernetes do
      # development provider
      provider :kind

      add_plugin :rails_app do
        # make the app available via localhost
        hostname 'localhost'
        tls_enabled false
      end
    end
  end
end

All the Docker config is defined in one place and applied to each environment.

tip

Given the example code above, the Rails app should be available on localhost after being deployed to the local Kind cluster. If you'd rather use the production hostname instead (myapp.com in the example), you'll need to add an entry in your /etc/hosts file. It is also possible to use a tool like curl by passing the Host header, eg:

curl -H 'Host: myapp.com' http://localhost

TLS certificates are not supported by kuby-kind.