Presented at Euroclojure June 2014.

1. CLOJURE AT A POST OFFICE

3. HTTP-KIT
• AWS C1-Medium!
• 7GB Ram!
• 8 Cores
• 313,852 Concurrent Users!
• 4756.79 Requests Per Second

4. If payment is success: display amount remaining on bill!
If payment fails: display error
Make a payment on a bill!
- Not necessarily a full payment
POST /bills/:bill-id/payments
Session: user-id
Post Data: amount
1. GET credit card token for user!
1.1. POST request to payment gateway!
2. GET how much was left to be payed

5. CANDIDATES
• Synchronous promises!
• Promise monad let/do!
• Raw promises!
• Raw callbacks!
• core.async!
• Lamina pipeline!
• Meltdown (LMAX
Disrupter)!
• Pulsar promises!
• Pulsar Actors

6. SOLUTION 0:
SYNCHRONOUS
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
""(let'[token"""""""(auth/card/token"user*id)"
""""""""details"""""(bill/details"bill*id)"
""""""""transaction"(payment/bill"bill*id"amount"@token)]"
""""(if'(success?"@transaction)"
""""""(render/remaining/response"@details"amount)"
""""""error*response)))"

7. SOLUTION 1.1:
PROMISE MONAD DO
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
"""""(do'[token"""""""(auth/card/token"user*id)"
""""""""""transaction"(payment/bill"bill*id"amount"token)"
""""""""""details"""""(bill/details"bill*id)]"
"""""""""(return"
"""""""""""(if'(success?"transaction)"
"""""""""""""(render/remaining/response"details"amount)"
"""""""""""""error*response))))

8. SOLUTION 1.2:
PROMISE MONAD LET/DO
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
"""""(let'[token*req"""(auth/card/token"user*id)"
"""""""""""details*req"(bill/details"bill*id)]"
"""""""(do'[token"""""""token*req"
""""""""""""transaction"(payment/bill"bill*id"amount"token)"
""""""""""""details"""""details*req]"
"""""""""""(return"
"""""""""""""(if'(success?"transaction)"
"""""""""""""""(render/remaining/response"details"amount)"
"""""""""""""""error*response)))))

9. SOLUTION 1.3:
PROMISE MONAD LET/DO/DO
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
"""""(let'[token*req"""(auth/card/token"user*id)"
"""""""""""details*req"(bill/details"bill*id)]"
"""""""(do'[token"""""""token*req"
""""""""""""transaction"(payment/bill"bill*id"amount"token)]"
"""""""""""(if'(success?"transaction)"
"""""""""""""(do'[details"details*req]"
"""""""""""""""""(return"(render/remaining/response"details"amount)))"
"""""""""""""(return"error*response)))))

10. SOLUTION 3:
RAW PROMISES
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
"""""(let'[transaction*req"(*>"(auth/card/token"user*id)"
"""""""""""""""""""""""""""""""(then"(partial"payment/bill"bill*id"amount)))"
"""""""""""details*req"""""(bill/details"bill*id)]"
"""""""(when"transaction*req"details*req"
"""""""""(fn'[transaction"details]"
"""""""""""(if'(success?"transaction)"
"""""""""""""(render/remaining/response"details"amount)"
"""""""""""""error*response)))))

11. SOLUTION 4:
RAW CALLBACKS
Not"Viable

12. SOLUTION 5:
CORE.ASYNC
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
"""""(go"(let'[token"""""""(auth/card/token"user*id)"
"""""""""""""""details"""""(bill/details"bill*id)"
"""""""""""""""transaction"(payment/bill"bill*id"amount"(<!"token))]"
"""""""""""(if'(success?"(<!"transaction))"
"""""""""""""(render/remaining/response"(<!"details)"amount)"
"""""""""""""error*response))))

13. SOLUTION 6:
LAMINA PIPELINE
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
"""""(let'[details*req"(bill/details"bill*id)]"
"""""""(pipeline"(auth/card/token"user*id)"
"""""""""""""""""(partial"payment/bill"bill*id"amount)"
"""""""""""""""""(fn'[transaction]"
"""""""""""""""""""(if'(success?"transaction)"
"""""""""""""""""""""(on/realized"details*req"
""""""""""""""""""""""""""""""""""(fn'[details]"
""""""""""""""""""""""""""""""""""""(render/remaining/response"details"amount)))"
"""""""""""""""""""""error*response)))))

14. SOLUTION 7:
MELTDOWN
No"point

15. SOLUTION 8:
PULSAR PROMISES
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
""#(let'[token"""""""(auth/card/token"user*id)"
"""""""""details"""""(bill/details"bill*id)"
"""""""""transaction"(payment/bill"bill*id"amount"@token)]"
""""(if'(success?"@transaction)"
""""""(render/remaining/response"@details"amount)"
""""""error*response)))

16. SOLUTION 9:
PULSAR ACTORS
Not"Appropriate

17. (GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
""(let'[token"""""""(auth/card/token"user*id)"
""""""""details"""""(bill/details"bill*id)"
""""""""transaction"(payment/bill"bill*id"amount"@token)]"
""""(if'(success?"@transaction)"
""""""(render/remaining/response"@details"amount)"
""""""error*response))) Synchronous
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
""(go"(let'[token"""""""(auth/card/token"user*id)"
""""""""""""details"""""(bill/details"bill*id)"
""""""""""""transaction"(payment/bill"bill*id"amount"(<!"token))]"
""""""""(if'(success?"(<!"transaction))"
""""""""""(render/remaining/response"(<!"details)"amount)"
""""""""""error*response)))) core.async
(GET""/bills/:bill*id/payments""[bill*id"user*id"amount]"
""#(let'[token"""""""(auth/card/token"user*id)"
"""""""""details"""""(bill/details"bill*id)"
"""""""""transaction"(payment/bill"bill*id"amount"@token)]"
"""""(if'(success?"@transaction)"
"""""""(render/remaining/response"@details"amount)"
"""""""(error/response)))) Pulsar

18. ""def"payBill(billId:"Integer,"userId:"Integer,"amount:"Integer):Future[Option[Json]]"="{
""""val"seq"="for"{
""""""token"<*"Auth.cardToken(userId)
""""""tr"<*"Payment.bill(token)
""""}"yield"tr
"
""""async"{
""""""val"transactionProcess"="await(seq.run)
""""""val"detailProcess"="await(BillOps.details(billId))
""""""for"{
""""""""transaction"<*"transactionProcess
""""""""detail"<*"detailProcess
""""""}"yield"renderRemainingResponse(amount,"detail)
""""}
""}
SCALA

19. REQUESTS PER SECOND

21. CQRS!
• Want fast reads. Reduce the
number of queries.!
• Don't want to have to
update write code every
time we add a new reader.!
• Don't want to have to
update reader every time
there's a new writer.!
• Would be great to have an
event stream to re-calculate
current state.

22. 1.#Just#write#to#normalised#copy#
1.1.# Just#read#everything#every#time#
1.2.# Read#and#cache#
1.2.1.# Cache#the#page#
1.2.2.# Cache#the#intermediate#data;structure#
2.#Just#write#to#views#
2.1.# Direct#write#
2.2.# Event#stream#
2.2.1.# Persisted#
2.2.1.1.# Domain#events#
2.2.1.1.1.#Live#update#
2.2.1.1.2.#Async#update#
2.2.1.2.# CRUD#event#
2.2.1.2.1.#Live#update#
2.2.1.2.2.#Async#update#
2.2.2.# Ephemeral#
2.2.2.1.# Domain#events#
2.2.2.1.1.#Live#update#
2.2.2.2.# CRUD#event#
2.2.2.2.1.#Live#update#
3.#Write#to#views#and#normalized#copy##
3.1.# Direct#write#
3.2.# Event#stream#
3.2.1.# Persisted#
3.2.1.1.# Domain#events#
3.2.1.1.1.#Live#update#
3.2.1.1.2.#Async#update#
3.2.1.2.# CRUD#event#
3.2.1.2.1.#Live#update#
3.2.1.2.2.#Async#update#
3.2.2.# Ephemeral#
3.2.2.1.# Domain#events#
3.2.2.1.1.#Live#update#
3.2.2.2.# CRUD#event#
3.2.2.2.1.#Live#update#
3.3.# Write#to#normalized#keyspace#causing#
trigger#
3.3.1.# Direct#update#to#views#
3.3.2.# Event#to#be#published#
3.3.2.1.# Persisted#
3.3.2.1.1.#Live#Update#
3.3.2.1.2.#Async#update#
3.3.2.2.# Ephemeral#
3.3.2.2.1.#Live#Update

23. Write
!
!
Cassandra
Service A
Service B Index Maintainer
Notify
Read Write
Rabbit MQ
Publish
Triggers

24. CASSANDRATRIGGERS
• Can just throw the Clojure
jar in there!
• Everything is byte buffers!
• Need to know the type of
fields out of band!
• One class per trigger per
table!
• Bizarre key names (format
changes depending on value
type)

26. User
Service
Mail
Service
Provider
Service
Cassandra
IOS Web Android

27. User
Service
Authentication
Multi Factor
Authentication
Authorisation
User Profile
Password Reset