change to using service discovery for backend

app/controllers/application_controller.rb

@@ -1,4 +1,6 @@
 require 'net/http'
+require 'resolv'
+require 'uri'
 
 class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
@@ -44,15 +46,21 @@ def health
  end
 
  def crystal_addr
- crystal_addr = ENV["BACKEND_API"]
- # The address will be of the form, http:https://172.17.0.5:5432, so we add a trailing slash
- crystal_addr.sub(/^http:/, 'http:') + "/crystal"
+ expand_url ENV["CRYSTAL_URL"]
  end
 
  def backend_addr
- backend_addr = ENV["BACKEND_API"]
- # The address will be of the form, http:https://172.17.0.5:5432, so we add a trailing slash
- backend_addr.sub(/^http:/, 'http:') + "/"
+ expand_url ENV["NODEJS_URL"]
+ end
+
+ # Resolve the SRV records for the hostname in the URL
+ def expand_url(url)
+ uri = URI(url)
+ resolver = Resolv::DNS.new()
+ srv = resolver.getresource("_#{uri.scheme}._tcp.#{uri.host}", Resolv::DNS::Resource::IN::SRV)
+ uri.host = srv.target.to_s
+ uri.port = srv.port.to_s
+ uri.to_s
  end
 
  before_action :discover_availability_zone

mu.yml

@@ -5,6 +5,6 @@ service:
  port: 3000
  pathPatterns:
  - /*
- networkMode: awsvpc
  environment:
- BACKEND_API: "http:https://api.internal.service:80"
+ CRYSTAL_URL: "http:https://ecsdemo-crystal.${_SERVICE_DISCOVERY_NAMESPACE}/crystal"
+ NODEJS_URL: "http:https://ecsdemo-nodejs.${_SERVICE_DISCOVERY_NAMESPACE}/"