Cloud computing, DevOps, IOT or just connecting the local active directory or {put any LOB system here}: The applications we build are getting more and more distributed. Now guess who's guilty if your application fails, because there was some error outside of your code (even outside of your control influence)? This session is about designing, developing and deploying rock solid applications.

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Defensive Programming,
Daniel Fisher
Resilience Patterns &
Antifragility

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I’m a technician & always concerned about bandwidth
So I ask you to send one packet instead of two
DANIEL
My name is
Any further questions? Just Ask!

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software
I design, develop, deploy, teach, train, coach and speak
HTML5 & WEB, DATA ACCESS & PERFORMANCE,
SCALABLE & TESTABLE DESIGN, DISTRIBUTED SYSTEMS
& SERVICES, SECURITY & TRUST
lennybacon.com my blog url
@lennybacon my twitter handle
info@danielfisher.com my smtp
find my services at danielfisher.com

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THAT IS ALL THAT I DEEPLY BELEVE IN
D I S C L A I M E R
IT FITS MY SHOES
IT MIGHT NOT FIT YOURS
THIS PRESENTATION CONTAINS MY
PERSONAL VIEW ON THE WORLD
IT IS BASED ON MY EXPERIENCE IN SOFTWARE DEVELOPMENT PROJECTS SINCE 1996
MOST THINGS I LEARNED FROM PAIN
OTHERS FROM MOMENTS OF GRACEFULNESS, BRAVENESS & SUCCESS

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CHAPTER 1
Software Development: A world of fear

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https://www.flickr.com/photos/38295844@N05/4980776534/

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https://www.flickr.com/photos/pagedooley/2398572388/

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http://www.city-data.com/forum/anchorage/692696-anchorage-here-we-come-finally.html

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BOSS

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“Office Space” by Mike Judge / Twentieth Century Fox Film Corporation

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CHANGE

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https://www.flickr.com/photos/bluedharma/89186151

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https://www.flickr.com/photos/armydre2008/3144377781

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RELEASE

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Time
Change
Big…
Small…

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FAIL

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https://www.flickr.com/photos/38403488@N08/5100179116

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I have not failed!
I've just found
10,000 ways that
won't work …Thomas Edison

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CHAPTER 2
Paranoia basics: Defensive programming

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https://www.flickr.com/photos/ajahan/8413794849

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Yoda Conditions
if (variable.Equals("literal"))
{
...
}
if ("literal".Equals(variable))
{
...
}

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Check Collections for Null
var files = SomeApi.GetFileList();
if (files != null)
{
for (var i = 0; i < files.length; i++)
{
...
}
}

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All classes are sealed by default
public class Class1
{
...
}
internal sealed class Class1
{
...
}

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DDD Value Object Input Validation
public sealed class ZipCode
: IValueObject
{
public ZipCode(int value)
{
// Input validation!!!
Value = value;
}
public int Value { get; private set;}
}

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CHAPTER 3
Advanced paranoia tactics: Robustness

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CULTURE
IT’S ALL ABOUT

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Finding Bugs is
good and mustn’t
be punished!
It makes code
less buggy!

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Finding Bugs in
tests is even
better!
No customer will
even face them!

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Try to break, burn,
shoot and drown
it together!
I call it
Breakstorming!

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CHAPTER 4
Professional Paranoia: Resilience patterns

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A distributed system
is one in which the failure
of a computer you didn't
even know existed can
render
your computer unusable
http://research.microsoft.com/en-us/um/people/lamport/pubs/distributed-system.txt

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Topology changes
Networks fail
Latency varies by location
Bandwidth differs by location
Things get hacked

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Servers get rebooted
Code has bugs
Other users might use it different
Failover means offline
Processing time varies by amount of data
Environments differ
File system is not always available

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Life is not a
walk in the park.
neither is software!

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Success is the ability
to go from one
failure to another
with no loss of
enthusiasm.
WinstonChurchill

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Scale like a boss
Asynchronicity
No one waiting for an error
Bulkheads & Replays
Loose coupling for the win
But dare you forget the dead letters
No cascading failures and stack trace

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BASE OVER ACID
Atomic, Consistent, Isolated and Durable
solutions are not a silver bullet.
Basic Availability, Soft-state and Eventual consistency work
better in most distributed scenarios.
BUT YOU MUST THINK DIFFERENT FOR BASE
Use a more relaxed consistency model to reduce coupling
Queues are as transactional as databases

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Idempotency
Non-idempotency is complicated to handle
and increases coupling between participants.
stateless stateless stateless
THIS ALSO REQUIRES YOU TO THINK DIFFERENT
But in the end it is nothing more than divide and conquer with an eye on the results
Functional programming and
immutable types for the win.

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Monitor & Audit
Measure to gain latency control and detect non-
timely responses before they time out.
Learn more about the life of your system to predict its behavior.
If you can’t debug, log is your friend
Respond to detected failures.
20% - 40% logging code
Auditing and Logging can even be party of your architecture

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Retry Pattern
https://www.flickr.com/photos/st3f4n/143623217

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Circuit Breaker Pattern
https://www.flickr.com/photos/qubodup/8278039181

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Leader Election Pattern
http://moonbasetshirts.limitedrun.com/products/557785-palpatine-vader-2016

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CompensatingTransaction Pattern
https://www.flickr.com/photos/susivinh/16341538221

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CHAPTER 5
Things that gain from disorder: Antifragility

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Nassim Nicholas Taleb wrote two interesting books
about how economical systems behave.
He focusses on what happens under
stress and on unexpected occurrences
of events.
The black swan
Antifragility

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Antifragility
Resilience
Robustness
Fragile
Time
Value/Correctness/Stability/…

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What Doesn't Kill You
Makes You Stronger
Every time something catastrophic
happens that you take on and survive…
… your team and you code becomes
Stronger, Better, Faster, More

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Asymmetric information & options
An opportunity to cope with
the lack of knowledge
ST R AT E GY
Business, Architecture & Code
Long Term vs Short Term
Sustainability vs Reward

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Thank you!
danielfisher.com my company
lennybacon.com my blog url
@lennybacon my twitter handle
info@danielfisher.com my smtp