I start with the basics of the strangler pattern approach and then go to some harder parts of it, like the Anti-Corruption Layer. I also briefly discuss two projects I worked on using this pattern.

1. D R S T R A N G L E R
& M R H Y P E
S T R A N G L E R PAT T E R N I N P R A C T I C E

2. Michał Kurzeja
CTO @ Accesto
TW: @michalKurzeja
michal@accesto.com

3. T H I S TA L K S I S A B O U T
• Where legacy comes from?
• Why it is worth to get rid of legacy…
• … and how to make it properly?
• How not to hurt yourself
• Examples

4. T H I S TA L K I S N O T A B O U T
• How to test
• How to refactor classes/methods
• Silver bullet step-by-step approach

5. Bad practices
„Mr Hype”
Good practices
„Dr Strangler”

6. L E G A C Y C O D E

8. L E G A C Y ! = I N H E R I T E D C O D E

9. E X P E C TAT I O N S

10. R E A L I T Y

11. Q U A L I T Y D E C R E A S E S I N T I M E
- L A C K O F T H E „ B O Y S C O U T ” R U L E
0
17,5
35
52,5
70
2010 2011 2012 2013

12. R E S U LT S ? I S S U E S :
• Complicated code
• Harder to write tests
• Difficult deployment
• Reluctance of developers
• Hard to develop

13. H O W T O C O N V I N C E B U S I N E S S
• Slower development
• competitors might be faster
• increased costs
• HR issues: harder recruitment, more people leaving
• Lots of bugs, angry customers
• It might explode at any time ;)

14. 2 0 1 2 , K N I G H T C A P I TA L G R O U P
$460 mln loss in 45 minutes

15. W H AT C A N W E D O ?

16. R E W R I T E F R O M S C R AT C H

17. F R O M 9 0 % T O 0 %
O F M A R K E T S H A R E
D E C L I N E O F N E T S C A P E
L O S T I T T O I N T E R N E T E X P L O R E R !

18. K E E P O N G O I N G

19. R E FA C T O R ?

21. Rewrite from scratchKeep on going
Refactor STRANGLE!
FUN
RISK

22. S T R A N G L E R PAT T E R N

29. G AT E WAY / FA C A D E

30. G AT E WAY - B U I L D I T L E A N
server {
listen 80;
server_name domain.com;
location /profile {
proxy_pass http://10.0.3.10:80;
}
location /news {
proxy_pass http://10.0.3.10:80;
}
proxy_pass http://10.0.3.20:80;
}

31. G AT E WAY - P O S S I B L E S O L U T I O N S
• API - Open Source
• Kong
• API - Paid
• AWS API Gateway
• WWW
• HaProxy
• Nginx/Apache/…

32. S TA R T W I T H C AT C H A L L

34. S H A R E D D ATA B A S E

35. D I S T R I B U T E D S H I T

36. S P L I T D ATA B A S E S
• Scheduled sync (cron)
• Events (required change in legacy)
• DB Triggers
• Transaction log (Binlog -> Kafka)

37. A P I

39. B O U N D A R I E S

40. ANTI-CORRUPTION LAYER

41. A C L

48. L E G A C Y I N A B O X

51. I N P R A C T I C E

52. L O N G T I M E A G O …
• Market leader
• Project started in 2010, we took over in 2016
• Customers: banks, political parties - no downtime
allowed ;)

53. N O F R O N T- C O N T R O L L E R

54. „ C U T E ” V E R S I O N I N G

55. „ M A G I C ” S T R U C T U R E

56. „ B U L L E T P R O O F ” C O N F I G
It was $_SERVER[SERVER_NAME];

57. „ R E A D A B L E ” C O D E

58. Generally….

59. S E V E R A L G R AY H A I R L AT E R

60. • Monorepo
• Apache as facade
• Anti-Corruption Layer -> API
• JSON Web Token
• Configuration by env variables

62. • 100% automated deployment (on Kubernetes)
• Business is very happy
• Programmers are still alive (and work for us)

63. M I S TA K E S
W H AT C O U L D B E D O N E B E T T E R

64. F E AT U R E T O G G L E

65. J W T F R O M D AY 1 0

66. B E T T E R A C L

67. I S S U E S

68. P R O S
• Small risk, less stress, quick releases
• Instant effects
• Both business and developers happy

69. S E C O N D A P P R O A C H - A C L *
* M O D I F I E D A B I T

70. M O D E R N A C L L E G A C Y
https://github.com/VaughnVernon/IDDD_Samples/tree/master/iddd_collaboration/src/main/java/com/saasovation/
collaboration/port/adapter/service

71. M O D E R N A C L L E G A C Y
APIREPO

72. class Currency
{
private $isoCode;
private $default;
private $ratio;
}
M O D E R N - C U R R E N C Y M O D E L

73. interface CurrencyRepository
{
public function findAll();
public function getDefault();
public function find(string $isoCode);
public function save(Currency $currency);
}
M O D E R N - C U R R E N C Y R E P O S I T O RY

74. class Internal_CurrencyController extends Internal_Controller_InternalController
{
public function listcurrenciesAction()
{
$this->checkIp();
$this->getResponse()->setHeader('Content-type', 'application/json');
$mCurrency = new Default_Model_Currency();
/** @var Zend_Db_Table_Rowset $currencies */
$currencies = $mCurrency->fetchAll('status = "active"');
$this->getResponse()
->setBody(json_encode($currencies->toArray()))
->setHttpResponseCode(200);
}
}
L E G A C Y - C U R R E N C Y FA C A D E

75. interface CurrencyAdapter
{
public function findAll(): array;
}
A C L - C U R R E N C Y A P I I N T E R FA C E

76. class LegacyCurrencyAdapter implements CurrencyAdapter
{
public function findAll(): array
{
$response = $this->client->request('GET', 'listCurrencies');
$currencies = json_decode((string) $response->getBody(), true);
return array_map(function ($row) {
$currency = $this->currencyTranslator->createFromArray($row);
if ($exCurrency = $this->currRepo->find($currency->isoCode())) {
$currency->setRatio($exCurrency->getRatio());
$currency->setDefault($exCurrency->getDefault());
}
return $currency;
}, $currencies);
}
}
A C L - C U R R E N C Y A P I

77. class LegacyCurrencyTranslator implements CurrencyTranslator
{
public function createFromArray(array $data)
{
$default = filter_var($data['default'], FILTER_VALIDATE_BOOLEAN);
$ratio = filter_var($data['value'], FILTER_VALIDATE_FLOAT);
return new Currency($data['code'], $ratio, $default);
}
}
A C L - C U R R E N C Y T R A N S L AT O R

78. W H AT N O T T O D O

79. R O U T I N G I N L E G A C Y / M O D E R N

80. L A C K O F A N T I - C O R R U P T I O N L AY E R

81. P L A N F I R S T,
C O D E L AT E R

83. GETTING STARTED WITH DDD WHEN SURROUNDED BY
LEGACY SYSTEMS
E R I C E VA N S

85. W R I T E S O F T WA R E T H AT
I S E A S Y T O S T R A N G L E

86. Michał Kurzeja
CTO @ Accesto
@michalKurzeja
michal@accesto.com
Thanks!