PaaS service discovery example

app.rb

# frozen_string_literal: true
require 'http'
require 'sinatra'
require 'time'

BACKEND = 'http://backend.apps.internal:8080'

get '/' do
  app = ENV.fetch('APP')

  <<-RESPONSE
  #{app}
    #{Time.now}
    #{ENV.fetch('CF_INSTANCE_INDEX')}
    #{ENV.fetch('CF_INSTANCE_ADDR')}
    #{ENV.fetch('CF_INSTANCE_IP')}
    #{ENV.fetch('CF_INSTANCE_INTERNAL_IP')}
  -----
  #{app == 'frontend' ? HTTP.get(BACKEND).body.to_s : ''}
  RESPONSE
end

config.ru

require File.expand_path('../app.rb', __FILE__)
run Sinatra::Application

Gemfile

source 'https://rubygems.org'

gem 'http'
gem 'sinatra'

Instructions.md

PaaS service discovery example

1. Save the files in the gist
2. Run chmod +x push.sh && . !$
3. Run chmod +x test.sh && . !$

manifest.yml

---
applications:
  - name: frontend
    buildpack: ruby_buildpack
    instances: 2

    host: frontend
    domain: cloudapps.digital

    env:
      APP: frontend

  - name: backend
    buildpack: ruby_buildpack
    instances: 2

    host: backend
    domain: apps.internal

    env:
      APP: backend

PaaS Service Discovery & Internal Networking

PaaS Service Discovery & Internal Networking

push.sh

#!/usr/bin/env bash

cf push -f manifest.yml

cf add-network-policy frontend \
                      --destination-app backend \
                      --protocol tcp \
                      --port 8080

cf restart frontend
cf restart backend

test.sh

#!/usr/bin/env bash

url="https://$(cf apps | grep frontend | awk '{print $6}')"

watch -d -n1 "curl --silent $url"

grep foo | awk '{ something}' => awk '/foo/ { something }'