danielfisher.com

Defensive Programming,

Daniel Fisher

Resilience Patterns &

Antifragility

danielfisher.com

I’m a technician & always concerned about bandwidth

So I ask you to send one packet instead of two

DANIELMy name is

Any further questions? Just Ask!

danielfisher.com

softwareI 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 handleinfo@danielfisher.com my smtp

find my services at danielfisher.com

danielfisher.com

THAT IS ALL THAT I DEEPLY BELEVE IN

D I S C L A I M E R

IT FITS MY SHOESIT MIGHT NOT FIT YOURS

THIS PRESENTATION CONTAINS MYPERSONAL VIEW ON THE WORLDIT IS BASED ON MY EXPERIENCE IN SOFTWARE DEVELOPMENT PROJECTS SINCE 1996

MOST THINGS I LEARNED FROM PAIN

OTHERS FROM MOMENTS OF GRACEFULNESS, BRAVENESS & SUCCESS

danielfisher.com

CHAPTER 1Software Development: A world of fear

danielfisher.com

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

danielfisher.com

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

danielfisher.com

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

danielfisher.com

BOSS

danielfisher.com

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

danielfisher.com

CHANGE

danielfisher.com

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

danielfisher.com

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

danielfisher.com

RELEASE

danielfisher.com

Time

Chang

e Big

…

Sm

all

…

danielfisher.com

danielfisher.com

FAIL

danielfisher.com

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

danielfisher.com

I have not failed!I've just found10,000 ways thatwon't work …

Thomas Edison

danielfisher.com

CHAPTER 2Paranoia basics: Defensive programming

danielfisher.com

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

danielfisher.com

Yoda Conditions

if (variable.Equals("literal")){

... }

if ("literal".Equals(variable)){

... }

danielfisher.com

Check Collections for Null

var files = SomeApi.GetFileList();

if (files != null){

for (var i = 0; i < files.length; i++){

...

}

}

danielfisher.com

All classes are sealed by default

public class Class1{...

}

internal sealed class Class1{...

}

danielfisher.com

DDD Value Object Input Validation

public sealed class ZipCode: IValueObject

{public ZipCode(int value)

{

// Input validation!!!

Value = value;

}

public int Value { get; private set;}

}

danielfisher.com

CHAPTER 3Advanced paranoia tactics: Robustness

danielfisher.com

CULTUREIT’S ALL ABOUT

danielfisher.com

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

danielfisher.com

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

danielfisher.com

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

danielfisher.com

CHAPTER 4Professional Paranoia: Resilience patterns

danielfisher.com

A distributed systemis one in which the failureof a computer you didn'teven know existed can

renderyour computer unusable

http://research.microsoft.com/en-us/um/people/lamport/pubs/distributed-system.txt

danielfisher.com

danielfisher.com

Topology changes

Networks failLatency varies by location

Bandwidth differs by location

Things get hacked

danielfisher.com

Servers get rebooted

Code has bugsOther users might use it different

Failover means offline

Processing time varies by amount of data

Environments differFile system is not always available

danielfisher.com

Life is not awalk in the park.

neither is software!

danielfisher.com

Success is the abilityto go from onefailure to anotherwith no loss of

enthusiasm.Winston Churchill

danielfisher.com

Scale like a boss

AsynchronicityNo one waiting for an error

Bulkheads & Replays

Loose coupling for the winBut dare you forget the dead letters

No cascading failures and stack trace

danielfisher.com

BASE OVER ACIDAtomic, Consistent, Isolated and Durablesolutions are not a silver bullet.

Basic Availability, Soft-state and Eventual consistency workbetter 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

danielfisher.com

IdempotencyNon-idempotency is complicated to handleand 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 andimmutable types for the win.

danielfisher.com

Monitor & AuditMeasure 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 codeAuditing and Logging can even be party of your architecture

danielfisher.com

Retry Pattern

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

danielfisher.com

Circuit Breaker Pattern

https://www.flickr.com/photos/qubodup/8278039181

danielfisher.com

Leader Election Pattern

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

danielfisher.com

Compensating Transaction Pattern

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

danielfisher.com

CHAPTER 5Things that gain from disorder: Antifragility

danielfisher.com

Nassim Nicholas Taleb wrote two interesting booksabout how economical systems behave.

He focusses on what happens understress and on unexpected occurrencesof events.

The black swan

Antifragility

danielfisher.com

Antifragility

Resilience

Robustness

Fragile

Time

Valu

e/C

orr

ect

ness

/Sta

bili

ty/…

danielfisher.com

What Doesn't Kill YouMakes You StrongerEvery time something catastrophichappens that you take on and survive…

… your team and you code becomes

Stronger, Better, Faster, More

danielfisher.com

Asymmetric information & options

An opportunity to cope withthe lack of knowledge

S T R A T E GYBusiness, Architecture & Code

Long Term vs Short Term

Sustainability vs Reward

danielfisher.com

Thank you!

danielfisher.com my companylennybacon.com my blog url@lennybacon my twitter handleinfo@danielfisher.com my smtp