Slides from a talk about how Stuart managed to successfully move away from a stack to another within a few months, without stopping our business. It sounds easy, but as many of you might know it's very hard. Many of us tried and failed. We succeeded, this is how we did it and you may use our experience to make improve your chance to succeed with yours. We'll explain how we remodeled the Engineer team, and added workflow processes, slowly moving away from the old stack to the new one.

1. SUCCESS STORY: HOW TO SWITCH STACK WITHOUT DOWNTIME

2. THE LEADER OF URBAN & ON-DEMAND LOGISTICS

3. Our mission is to connect merchants,
customers and local couriers to speed-up
the way goods are transported in cities

4. 04
MERCHANTS TRUST US
GROWING LIST OF TOP-TIER REFERENCES ACROSS VERTICALS

5. 05
TEAM
GROWING AND TALENTED ORGANISATION
CLÉMENT BENOIT
Co-Founder & CEO
Resto-in founder
BENJAMIN CHEMLA
Co-Founder & VP
Sales
Citycake founder
DAMIEN BON
COO
BCG
INSEAD
Lehman Brothers
FABIEN PENSO
CTO
Process-One
CloudScreener
Causes
We manage a team of 80 people coming from the best companies

6. 06
ABOUT ME
1995: Started using Linux
1998: LinuxFr - a French Linux community website
1999: DBee - First company
Since 2010: Causes, BBC, Cloudscreener, Stuart
PAST EXPERIENCES
@fabienpenso
http://penso.info

7. Short Video

8. 08
INFRASTRUCTURE 2015

9. 09
SOFTWARE STACK 2015
Standard LAMP + RabbitMQ + Crontab
0% test
coverage
GPA: 3.40 90k LOC 150 SQL
tables

10. 10
API REQUESTS PROCESSED IN 2015
SLOW PHP REQUEST
PROCESSING
(INCLUDES PSEUDO
BACKGROUND
TASKS)
REACH MAX
AMOUNT OF PHP
PROCESSES
QUICKLY
MINIMUM INTERVAL
FOR TASKS IS 1
MINUTE
INEFFICIENT
STORAGE FOR
BACKGROUND
TASKS

11. 11
LOOKING FOR A NEW STACK OPTION

12. 12
HOW TO SWITCH: TWO PATHWAYS
Option A
Write all from the ground up,
new Rails project, then write a
script to move all existing data.
+ Clean code, no legacy
once moved.
- Can't rollback, long time
before seeing
improvements
- High chance of failure
Option B
Write small pieces of code to
work with the existing context/
environment.
+ Business doesn't stop,
can still add features, and
fix existing bugs
- Manage 2 platforms for
months, new code
connects to old storage
schema, must replicate
bad code structure

13. 13
QUICK CODE GENERATION
Automatic code generation - ActiveRecord Ruby
code from SQL tables
Backoffice - Install ActiveAdmin to view all AR
classes and records
Continuous Integration - Setup deployment
Gem - php_serialize, annotate, devise
# == Schema Information
#
# Table name: vehicle
#
# id :integer not null, primary key
# driver_id :integer
# brand :string(100)
# model :string(150)
# number_plate :string(20)
# color :string(45)
# insurance :string(255)
# vehicle_registration :string(255)
class Vehicle < ActiveRecord::Base
end

14. 14
RUNNING BOTH PLATFORM

15. Refactor Feature Flag Ruby Feedback
Encapsulate the
PHP feature within
a single function
call
Add a feature flag in
the PHP code to enable/
disable this call
QA team enable
the feature on
staging, and verify
it works as
expected
Implement the
next "feature"
Clone code in
Ruby, add an
opposite feature
flag
15
IMPLEMENTING NEW CODE
Production

16. 16
HAVE A PLAN
Split the legacy
codebase into
virtual modules
Rewrite an easy
one at first
Rewrite them in
order of
importance
Finish with low
priority non critical
code

17. 17
IMPROVE LEGACY CODE
Add AR model validation
class Job < ActiveRecord::Base
validates :expires_at, presence: true
validate :payment_ability, on: :create
def payment_ability
if !has_funds? && !credit_card
errors.add(:credit_card, "meaningful message")
end
end
end
Ruby
Run validation for every SQL
changes
Warn about invalid models on Slack

18. <?php
// … code
class EntityListener {
protected $sidekiqJobPusher;
public function __construct(TransactionQueueService $redisClient) {
$this->sidekiqJobPusher = $redisClient;
}
public function onUpdate($calledEntity, UnitOfWork $uow) {
$this->sidekiqJobPusher->performActiveJob("PhpJob",
[$calledEntityName, $id, 'php_after_updated', $changedValues], true, "php");
}
public function onInsert($calledEntity) {
$this->sidekiqJobPusher->performActiveJob("PhpJob",
[$calledEntityName, $id, 'php_after_created'], true, "php");
}
}
?>
PHP Method injections
18
IMPROVE LEGACY CODE

19. # app/models/concerns/php_callbacks.rb
module PhpCallbacks
def php_after_created(_options = {})
return if valid?
message = "#{self.class}: #{id} errors: #{errors.full_messages.to_sentence}"
Service::Slack.ping message, channel: "#exceptions-#{Rails.env}"
end
alias php_after_updated php_after_created
End
# app/jobs/php_job.rb
class PhpJob < ActiveJob::Base
queue_as :php
include JobLogger
ACCEPTED_METHODS = %w(php_after_updated php_after_created).freeze
def perform(klass_type, id, method, *args)
unless ACCEPTED_METHODS.include?(method)
raise ArgumentError.new("`method` can only be #{ACCEPTED_METHODS.join(' or ')}!")
end
klass = klass_type.constantize rescue nil
if klass && klass.method_defined?(method.to_sym)
object = klass.find(id)
object.send(method, *args)
end
end
end
Ruby validation execution
19
IMPROVE LEGACY CODE

20. 20
FEATURE FLAG
FEATURE FLAG: ABILITY TO TURN FEATURE ON/OFF
PHP
use OpensoftRolloutRollout;
use OpensoftRolloutStorageArrayStorage;
$rollout = new Rollout(new ArrayStorage());
$rollout->isActive('outgoing_email');
Ruby
require "redis"
require "rollout"
$redis = Redis.new
$rollout = Rollout.new($redis)
$rollout.active?(:outgoing_email)
https://github.com/opensoft/rollout (PHP)
https://github.com/fetlife/rollout (Ruby)

21. 21
REMOVE OVERENGINEERED CODE
TOO MANY SQL TABLES
Before: 150 tables
After: 90 tables
class DriverStatusType
include TypableModel
read_only_attr :id, :code, :name
defaults [
[1, "off_duty", "Off Duty"],
[2, "on_duty", "On Duty"],
[3, "busy", "Busy"],
[4, "pending", "Pending"],
[5, "rejected", "Rejected"]
]
end
DriverStatusType.find_by(id: 1)
DriverStatusType.find_by(code: :on_duty)

22. 22
MOVE API ENDPOINTS
List ALL API
endpoints currently
used looking at the
PHP logs
68 endpoints to move
Make a plan

23. 23
MOVE API ENDPOINTS
Move one non critical
API endpoint
Move by importance,
most critical first
Good potential: https://getkong.org
Be able to turn each
api endpoint on/off

24. Grape Routing Feedback
Implement the API
endpoint in Ruby
Move this API
endpoint to Ruby in the
nginx routing file on
staging
Implement the
next api endpoint
QA team verify it
works as
expected
24
MOVE API ENDPOINTS
Production

25. 25
MOVE API ENDPOINTS
TOOLS: LIST OUR QA USED FOR TESTING
Runscope.com
Selenium
Android Espresso
iOS xcode test
Postman and curl
Charles HTTP Proxy

26. 26
INFRASTRUCTURE 2016

27. 27
CLOSING: SOFTWARE STACK 2015
Standard LAMP + RabbitMQ + Crontab
0% test
coverage
GPA: 3.40 90k LOC 150 SQL
tables

28. 28
CLOSING: SOFTWARE STACK 2016
Grape + Sidekiq + Rails
70% test
coverage
GPA: 3.95 15k LOC 90 SQL
tables

29. How long to move all the
code
?

30. 30
CLOSING
ROOM FOR IMPROVEMENT: WHAT WOULD WE DO DIFFERENT?
Ability to have ephemeral servers Give more power to the QA
Engineers

31. @fabienpenso