Event Sourcing

PHPTour 2015

Transcript

1. Event Sourcing #PHPTour 2015 @MattKetmo
2. CQRS Event Sourcing Reactive DDD }Patterns to build & structure applications Not new buzzwords, exist for many years How can it help to scale horizontally? Today’s focus
3. Matthieu Moquet @MattKetmo @ BlaBlaCar for ~4 years
4. {Disclaimer Oriented for long lived apps.
 Overkill for RAD / CRUD / TODO apps. Use those patterns in moderation.
 There is no silver bullet. This talk aims to open your mind.
 Think different!
5. I/O
6. 90% ViewModels / Flexible Eventually consistent 10% Validation / Business rules Coherence (ACID) Read Write Fast & Scale
7. Use case bank accounts Account #1 ! 1337€ Account #2 ! 42€ Account #3 ! 10€ + Transfer money
8. Account ! id user_id amount User ! id name ...
9. Facade (Controller) Models (ORM) DB
10. //  Open  new  account   $account  =  new  Account();   $account-­‐>setAmount(0,  'EUR');   $em-­‐>persist($account);   $em-­‐>flush();   ! //  Credit  100  EUR   $account-­‐>setAmount(100,  'EUR');   $em-­‐>flush();   ! //  Debit  20  EUR   $account-­‐>setAmount(80,  'EUR');   $em-­‐>flush();
11. is not the solution When user process an operation on his account his doesn’t directly update his total amount of money We need a service that translate our business needs CRUD
12. Facade (Controller) Models (ORM) DB Service Layer (Business)
13. interface  BankAccountService     {          /**  @return  int  */          public  function  open();   !        /**  @return  Account  */          public  function  get($accountId);   !        /**  @return  Account[]  */          public  function  findAll($userId);   !        /**  @return  void  */          public  function  credit($accountId,  $balance);   !        /**  @return  void  */          public  function  debit($accountId,  $balance);   }  
14. CQS Command Query Separation }Each operation is either a Command or a Query, not both
15. Commands Queries Change the state of the system. Do not return anything. Does not change the state of the system. Return data. Write only Read only
16. Commands /**  @return  Account  */   public  function  get($accountId);   ! /**  @return  Account[]  */   public  function  findAll($userId); /**  @return  int  */   public  function  open();   ! /**  @return  void  */   public  function  credit($accountId,  $balance);   ! /**  @return  void  */   public  function  debit($accountId,  $balance); Should be void Queries
17. /**      *  @param  Uuid  $accountId    *    *  @return  void      */   public  function  open(Uuid  $accountId);   Let the client generate the identifier, not the infrastructure (database)
18. CQRS Command Query Responsibility Segregation }Like CQS but separate queries and commands in different classes
19. Command Facade Query Facade Command Service Query Service Models (ORM) DB
20. CQRS challenges the assumption that reading and writing are sharing the same abstractions Databases Models Apps
21. Command Facade Query Facade Command Handler Query Repository Command Models DB Read Models Command DTO Segregation of read and write is a radical form of decoupling
23. The interesting part about CQRS is not the pattern itself. But it allows to challenge established assumptions and opens new architectural options.
24. How to Scale
25. Now that the workflow of Read & Write has been separated. We can optimize each side separately.
26. asynchronously Since Command Handlers do NOT return anything, 
 then do the execution
27. Command Facade Command Handlers Commands Queueing Ack
28. ! $accoundId  =  AccountId::generate();   $command  =  new  OpenAccountCommand($accountId);   ! if  (/*  is  command  valid  */)  {          $commandBus-­‐>handle($command);   !        return  new  Response(                  null,                  $async  ?  202  :  201,  //  Accepted  :  Created                  ['Location'  =>  "/accounts/$accountId"]          );     }
29. $command  =  new  DebitCommand(          $accountId,            new  Money(20,  'EUR')   );   ! if  (/*  account  has  enough  money  */)  {          $commandBus-­‐>handle($command);   !        return  new  Response(null,  204);   }
30. Command tracking Scale workers Horizontally by instantiating more workers (subscribers) Generate an identifier per command to let the client tracks its status Rabbitmq, Kafka, Gearman, ……… make your choice on queues.io
31. Projections On the Read side you should prepare you data as it will be requested
32. Having only 1 data store for reads & writes does not scale (well) different usage different needs
33. Denormalize your data UI View models Statistic models Search index models API Read models ... Read models are faster than JOIN
34. • search & aggregations capabilities • horizontal scaling architecture (sharding, replication) • denormalization • fast Secondary data store to read your data
35. {      "user_id":  133742      "from":  "Paris",      "to":  "Luxembourg",      "by":  [          "Reims",            "..."      ],      "date":  "2015-­‐05-­‐11",   } Input (mysql)
36. [{      "trip":  {          "from":  "Paris",          "to":  "Luxembourg",          "date":  "2015-­‐05-­‐11",          "..."      },      "user":  {          "name":  "John  D",          "age":  29,          "grade":  "beginner",          "..."      }   }] Output (Elasticsearch) denormalized searchable
38. SELECT  tweets.*,  users.*      FROM  tweets   ! JOIN  users      ON  users.id  =  tweet.sender_id   ! JOIN  follows      ON  follows.followee_id  =  user.id   ! WHERE  follows.follower_id  =  $userId   ! ORDER  BY  tweets.time  DESC   LIMIT  100
40. Tweets stream DB Aggs Timelines {      "user_id":  1234567890      "status":  "Hello  World"      "timestamp":  1430491773   } ! [{      "tweet_id":  1234567890876543,      "username":  "MattKetmo",      "name":  "Matthieu  Moquet",      "timestamp":  1430491773,      "status":  "Hello  World",   },  {      "tweet_id":  1234567890886445,      ...   }]  
41. SELECT  tweets      FROM  timelines    WHERE  timeline_id  =  $userId    LIMIT  500
42. PageViewEvents DB Aggs Increment counters /month Google Analytics /day /hour total {      "eventType":  "PageViewEvent"      "timestamp":  1430491773,      "ipAddress":  "12.34.56.78",      "sessionId":  "abcd1234567890",      "pageUrl":  "/hello-­‐world",      "..."   }
43. Using Cassandra you need to: ‣ know the read requests before creating your data models ‣ create as many tables (ie. KeySpaces) than you have views ‣ denormalize the data (no join allowed) ’s keypoints
44. C* C* C* Primary Data C* Read Data User post message Endpoint
45. Multi Data Center Replication + Sharding + Cache
46. Command Command Handler Primary DB Projections View Models Message Bus Write Read Eventual Consistency {...} {...} {...} {...}
47. Event Sourcing change the way we store our primary data
48. If we know the events of the past, we can reconstitute the present. Event Sourcing
49. Event Sourcing Register only a series of events. Reconstitute the state of current "entity" by reading the past events.
50. the standard way Something happen State A State B Something happen (delta) (dropped) (stored) (delta) Time
51. the event sourcing way Something happen State A State B Something happen (stored) (reconstituted) (reconstituted) (stored) Time
52. [{        "uuid":  "110e8400-­‐e29b-­‐11d4-­‐a716-­‐446655440000",        "type":  "AccountWasOpen",        "recorded_on":  "2015-­‐05-­‐11T13:37:00Z",        "payload":  {}   },  {        "uuid":  "110e8400-­‐e29b-­‐11d4-­‐a716-­‐446655440000",        "type":  "AccountWasCredited",        "recorded_on":  "2015-­‐05-­‐11T14:42:00Z",        "payload":  {  "amount":  100,  "currency":  "EUR"  }   },  {      "..."   }] Event Store
53. Aggregates Domain models which serve the business logic using the ubiquitous language. Work as an isolated object (or graph of objects) which doesn’t reference any others. Can ensure only its own integrity.
54. //  Open  a  new  account   $accountId  =  AccountId::generate();   $account  =  BankAccount::open($accountId);   ! //  Add  some  money   $account-­‐>credit(new  Money(100,  'EUR'));
55. Records events Aggregates class  BankAccount  implements  AggregateRootInterface   {          //  ...   }
56. interface  AggregateRoot   {          /**            *  @return  DomainEventStream            */          public  function  getUncommittedEvents();   !        /**            *  @return  string            */          public  function  getAggregateRootId();   }
57. $accountId  =  AccountId::generate();   $account  =  BankAccount::open($accountId);   $account-­‐>credit(new  Money(100,  'EUR'));   ! //  Retrieve  event  stream   $events  =  $account-­‐>getUncommittedEvents();   //  -­‐  AccountWasOpen   //  -­‐  AccountWasCredited
58. class  BankAccount  extends  EventSourcedAggregateRoot   {          private  $accountId;   !        public  function  getAggregateRootId()          {                  return  $this-­‐>accountId;          }   !        public  static  function  open(AccountId  $accountId)          {                  $account  =  new  self();                  $account-­‐>apply(new  AccountWasOpen($accountId));   !                return  $account;          }   !        public  function  credit(Money  $balance)          {                  $this-­‐>apply(new  AccountWasCredited(                          $this-­‐>accountId,                          $balance-­‐>getAmount(),                          $balance-­‐>getCurrency()                  );          }   }
59. Reconstitute from events Aggregates
60. class  BankAccount  extends  EventSourcedAggregateRoot   {          //  ...              protected  function  applyAccountWasOpen(AccountWasOpen  $event)          {                  $this-­‐>accountId  =  $event-­‐>getAccountId();          }   !        protected  function  applyAccountWasCredited(AccountWasCredited  $event)          {                  $this-­‐>amount  +=  $event-­‐>getBalance();          }   !        protected  function  applyAccountWasDebited(AccountWasDebited  $event)          {                  $this-­‐>amount  -­‐=  $event-­‐>getBalance();          }   }
61. Aggregates Protect invariants
62. class  BankAccount  extends  EventSourcedAggregateRoot   {          //  ...   !        public  function  debit(Money  $balance)          {                  if  ($this-­‐>amount  <  $balance-­‐>getAmount())  {                          throw  new  NotEnoughMoneyException(                                  'Cannot  debit  more  than  current  amount'                          );                  }   !                return  $this-­‐>apply(new  AccountWasCredited(                          $this-­‐>accountId,                          $balance-­‐>getAmount(),                          $balance-­‐>getCurrency()                  ));                        }   }
63. Command + Event Sourcing
64. Command User intent Events Event Store Apply changes on system Primary DB Transactional append
65. class  BankAccountCommandHandler  extends  CommandHandler   {          public  function  handleOpenAccount(OpenAccount  $command)          {                  $account  =  BankAccount::open($command-­‐>getAccountId());   !                $this-­‐>repository-­‐>save($account);          }   !        public  function  handleCreditAccount(CreditAccount  $command)          {                  $account  =  $this-­‐>repository-­‐>load($command-­‐>getAccountId());                  $account-­‐>credit($command-­‐>getBalance());   !                $this-­‐>repository-­‐>save($account);          }   }
66. class  EventSourcingRepository  implements  RepositoryInterface   {          public  function  load($id)          {                  try  {                          $events  =  $this-­‐>eventStore-­‐>load($id);   !                        return  $this-­‐>aggregateFactory-­‐>create($events);                  }  catch  (EventStreamNotFoundException  $e)  {                          throw  AggregateNotFoundException::create($id,  $e);                  }          }   !        public  function  save(AggregateRoot  $aggregate)          {                  $events  =  $aggregate-­‐>getUncommittedEvents();   !                $this-­‐>eventStore-­‐>append(                          $aggregate-­‐>getAggregateRootId(),                            $events                  );          }   }
67. Event Sourcing PROS
68. Append Only Very fast data update Deleting data = new events
69. Immutable Infinite caching
70. Sharding Aggregates are self-reliant and don’t have external references No Joins
71. Complete historical data Being able to replay history is a major benefit both technically and for the business BI team will love it
72. No Database migration when updating the data DBA will love it
73. Event Sourcing CONS Well, not really
74. Ensure consistency How to avoid concurrent updates?
75. Load aggregate from EventStore: 150€ Create AccountWasDebited event Append event in datastore Example Two debits of 100€ must not be accepted if only 150€ left Load aggregate from EventStore: 150€ Create AccountWasDebited event Append event in datastore Event must NOT be appended twice
76. abstract  class  EventSourcedAggregateRoot  implements  AggregateRootInterface   {          private  $uncommittedEvents  =  array();   !        private  $playhead  =  -­‐1;            /**          *  Applies  an  event.            *  The  event  is  added  to  the  list  of  uncommited  events.          */          public  function  apply($event)          {                  $this-­‐>playhead++;   !                $this-­‐>uncommittedEvents[]  =  DomainMessage::recordNow(                          $this-­‐>getAggregateRootId(),                          $this-­‐>playhead,                          new  Metadata(array()),                          $event                  );          }   }
77. DBAL EventStore (MySQL) CREATE  TABLE  EventStore  (   !    `id`                    INT(11)  AUTO_INCREMENT,      `uuid`                BINARY(16),      `playhead`        INT(11),      `type`                TEXT,      `payload`          TEXT,      `metadata`        TEXT,      `recorded_on`  DATETIME,   !    PRIMARY  KEY  (`id`),   !    UNIQUE  KEY  `UNIQ_PLAYHEAD`  (`uuid`,  `playhead`)   );
78. E_TOO_MANY_EVENTS When your Aggregates are "long lived" it may be slow to read the full history eg. BankAccount
79. Snapshotting is a solution
80. Snapshotting Store the state of the aggregate and read only the events created after
81. Snapshotting Snapshot Snapshot Events States
82. TL;DR
83. Command Handler Events Event Store Command Auditing Read Model Event Listener Event Bus Projector Write Read Business rules Historical data Read / search index Side effects User intent View models
84. Frameworks C# / Java nCQRS Fohjin NEventStore LiteCQRS Lokad.CQRS Agr.CQRS Axon Framework JDON PHP Broadway Predaddy EventCentric.Core litecqrs-php ...?
85. qandidate-labs/broadway qandidate-labs/broadway-demo
86. GetEventStore.com Event Sourcing oriented database
87. cqrs.nu #MustRead
88. dddinphp.org Google Groups
89. Thank You! Slides available at moquet.net/talks/phptour-2015 Leave feedbacks @MattKetmo