Video and slides synchronized, mp3 and slide download available at http://bit.ly/12Y5G0c. David Craelius tells the story of Klarna building an online payment system in Erlang and their approach to solving the nightmare of technical debt accumulated during a period of fast expansion.Filmed at qconlondon.com. David Craelius has been working within the financial sector building core systems for online trading, banking and card processing the last twelve years. He was introduced to Erlang in 2006 and has been in love ever since. David became the CTO of Klarna, a fast growing Erlang based payments company in January 2011. Twitter: @dcraelius

1. leapfrogging with a rucksack
@dcraelius, CTO Klarna
#3031
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4. why do most (financial) companies lose
momentum after five years?
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5. 2005 2007 2008 2009 2010 2011 2012
The vision of safer and simpler
e-commerce was born. Our founders introduce
an idea: Invoice, that will change the way
people shop online.
Klarna’s journey
The 1000th store is signed. Investment
AB Öresund becomes
a partner in the company.
We expand and offer Finnish, Norwegian and
Danish consumers our payment solutions. We
also introduce our second payment service,
Account.
To expand further we need a company name that is viable for more than just the
Nordic countries. Therefore, we change our name to Klarna.
Klarna is growing and expanding rapidly by establishing
ourselves in Germany and the Netherlands. We also launch our
third payment service, Klarna Mobile.
Michael Moritz joins the board and we receive an investment
from Sequoia Capital.
With ~770 employees and growing, a new
product: Klarna Checkout and Austrian market
entry, the future is very bright.
Klarna receives financial backing from DST Global and
General Atlantic. We were nominated as Best International
Startup in the Crunchies Award.
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6. Safer Simpler More fun
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7. SolutionKlarna takes the risk
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8. keep it simple for the user (not
engineering)
• no pre-registration
• identify yourself using top of mind
information
• separate buying from paying
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9. https://klarna.com/
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10. so, why do most (financial) companies
lose momentum after five years?
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11. “technical
challenges”
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so you’re f@%ked, what to do?

13. the path to hell is paved with good
intentions
(and duct tape)
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14. neither tech nor biz embrace YAGNI
enough.
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15. sooo....what to
do?run for your life (or join a startup)
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16. lean or lazy?
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17. software engineering is about cost
effectiveness and lead time.
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18. • In a realm where every business has the same requirements, shrink-wrapped software
is appropriate. E.g. excel, SAP.
software engineering is about cost
effectiveness and lead time.
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19. • In a realm where every business has the same requirements, shrink-wrapped software
is appropriate. E.g. excel, SAP.
• In a realm where many businesses face the same problems, but there's a lot of
business-specific tweaking, the Java ecosystem is hard to beat. E.g. camel, hadoop,
oracle.
software engineering is about cost
effectiveness and lead time.
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20. • In a realm where every business has the same requirements, shrink-wrapped software
is appropriate. E.g. excel, SAP.
• In a realm where many businesses face the same problems, but there's a lot of
business-specific tweaking, the Java ecosystem is hard to beat. E.g. camel, hadoop,
oracle.
• In a soft-realtime, business specific realm, in-house development in something as
funky as Erlang is a great choice. E.g. telephone switches, stock quote distribution,
financial transactions etc = core stuff where you need to own your code & know your
tools.
software engineering is about cost
effectiveness and lead time.
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21. we chose a lean & decoupled strategy out
of our “dark pit of hell”.
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22. why?
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23. • YAGNI
why?
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24. • YAGNI
• availability is no longer optional.
why?
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25. • YAGNI
• availability is no longer optional.
• want to own our code and know our
tools.
why?
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26. Solutionfunctional & light weight tech
stack
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36. our soft-realtime tech stack
• erlang
• webmachine
• mochiweb
• Riak
• Rabbit MQ
• Chef
• Cloudstack
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37. YAGNI
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38. questions?
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39. Thank you!
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