Add reference to used certificate to host.

db/migrate/20160506065802_add_certificate_to_hosts.rb

@@ -0,0 +1,5 @@
+class AddCertificateToHosts < ActiveRecord::Migration
+  def change
+    add_reference :hosts, :certificate, index: true, foreign_key: true
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160428191808) do
+ActiveRecord::Schema.define(version: 20160506065802) do
 
   create_table "certificates", force: :cascade do |t|
     t.text     "key"
@@ -26,6 +26,9 @@ ActiveRecord::Schema.define(version: 20160428191808) do
     t.string   "uri"
     t.datetime "created_at",     null: false
     t.datetime "updated_at",     null: false
+    t.integer  "certificate_id"
   end
 
+  add_index "hosts", ["certificate_id"], name: "index_hosts_on_certificate_id"
+
 end