The Seneca Pattern at EngineYard Distill 2013 Conference

How do You Build Big Apps?

@rjrodgersenecajs.org

Tuesday 13 August 2013

TechnicalDebt


"A good plan, violently executed now,is better than a perfect plan next week."


You Must take onTechnical Debtor You Will Die


Sometimes,it Happens

AnywayTuesday 13 August 2013




NTSC 1941 Standard:

Black+White onlySignal encodes BrightnessEach Channel gets 6Mhz

Happy Days!


Color TelevisionThree Colors: Red, Green, Blue

Each Color needs 3MhzYou only have 6Mhzand you need 9Mhz!

Technical Debt FTW


You can't Break theold Black+White TVs


We must send the old brightness signal

White Light =30% Red

59% Green11% Blue

Send White, Red and Blue


You need to embed the color signals inside

the brightness signal


Color TV circuits aremore complicated

than they should be.


How do you ReduceTechnical Debt?


Longer and more detailed

Specifications!


Better LanguagesBetter Mental Models


How did theRomans do

Long Division?Tuesday 13 August 2013

LXXII MMMDCXIIL rem XII


How did theRomans doAddition?


1. Normalize: IV → IIII2. Concatenate: IIII + XI → IIIIXI3. Sort, descending: IIIIXI → XIIIII4. Reduce: XIIIII → XV

IV + XI = ?



Subtraction?Tuesday 13 August 2013

1. Normalize: XXIV → XXIIII2. Eliminate: XXIIII - XV → XIIII - V3. Expand: XIIII - V → VIIIIIIIII - V4. Repeat 2 and 3 until no moves left5. Reduce: IIIIIIIII → IX

XXIV - XV = ?



Multiplication?Tuesday 13 August 2013

III → 3VI → 6 → 110

III × VI = ?

3 × 001 × 0 = 03 × 010 × 1 = 63 × 100 × 1 = 12 18

bit shifting


How did theRomans doDivision?


they didn't


Roman Numerals have

Technical DebtTuesday 13 August 2013


Positional Number Systems make us

SmarterTuesday 13 August 2013

Mental Modelsfor Code


ProceduralFunctional

Object-OrientedLogic


Let's Experiment


Stand up.Everybody.


Is this a car?


YES NOStay standing Sit down

And stay down!








Objects areRoman Numerals


Objects break as system complexity

growsTuesday 13 August 2013

The need for design "patterns" is telling

you somethingTuesday 13 August 2013




Procedural code tends to

SpaghettiTuesday 13 August 2013




Functional and Logic are

More PowerfulTuesday 13 August 2013

WhatHappened?

Why didn't theyWin?


Technical Debt





What do weNeed?


A BetterMental Model


Easy to LearnEasy to Scale (humans)Easy to Scale (machines)Easy to ImplementEasy to build a Mental Model

Does not have to achieveVery Large Scale


We need Modelsthat Work forHuman Brains


Why isRuby on Rails

Popular?Tuesday 13 August 2013

Opinionated==

Shared Mental ModelTuesday 13 August 2013

Ruby on RailsModel is an

Accident of HistoryTuesday 13 August 2013

Let's Design aModel!


What does a Programmer do?

Self-contained AlgorithmsProcedural Business LogicFitting it all Together


Fitting it all Together is

the Hard PartTuesday 13 August 2013

What are HumansGood At?


If a card has a vowel on one side, it must have an odd number on the other.

Which cards should you turn over to verify that the rule is followed?


If you're drinking beer, you must be 21 or over.

Which patrons should you ask for ID?


You solved the second version using

Pattern MatchingTuesday 13 August 2013

Why is Pattern Matching

Such a Win?Tuesday 13 August 2013

We are Pattern MatchersIt scales for humans and machinesWorks without needing context


Why do I Care?


We build Minimum Viable Productsfor startups.It's all about technical debt.


Lucius Annaeus Seneca


The Seneca Strategy


EmbraceMicro-Services


Lots of Little ProcessesDo one thing, and do it WellCommunicate with Messages


Pattern Match onMessages


Messages are Asynchronous Send them any way you likeUse JSON as the data model


"Send Tweet"Acted on by Tweet Service

Example

{ command:"tweet" author:"@rjrodger" status:"Distill Rocks!"}


Tweet ServiceIf I see a message with this property:

Match the Pattern!

command:"tweet"

It's Mine!I don't care how you get it to me.

And I'll ignore anything else.


The Tweet Service can be written in

Any LanguageTuesday 13 August 2013

Keep it SmallDie and restart on Errors

Report your status


Level Up ThePattern Matching


Patterns map to Actions


cmd:drivestart engine, and go!

cmd:drive, type:hoverturn on anti-gravitystart engine and go!

Example


Two Rules to make this Unique

1. More properties always wins2. Check properties alphabetically


cmd:drive

cmd:drive,type:hover

Mappingcmd: drivetype: wheelspeed: 50

cmd: drivetype: hoverspeed: 100


One More Thing


Layers


When you add a pattern:If the pattern Already Exists,

Keep the Old Action,so you can use it

inside the New Action


cmd:drivestart engine, and go!

cmd:drivecall prior actionset speed to speed

Example


Implementation

senecajs.org


Let's build stuff!


Blog Data Layer

Platform-as-a-Service


the actions are

Blog

cmd:draft, post:contentcmd:publish, post:idcmd:redact, post:idcmd:homepagecmd:comment, post:id, comment:comment


action, not abstractioneasy to learn

easy to modifyeasy to maintainself-documenting

Win


the actions are

Data Layer

cmd:save, name:entitycmd:load, name:entitycmd:list, name:entitycmd:remove, name:entity


save some data

cmd: save, name: product,data: { name: Apple, price: 1.99 }


load some data

cmd: load, name: product,query: { name:Apple }


implement the actions

cmd:saveinsert into table name values data

cmd:loadselect * from name where query


add caching

cmd:savecall prior actionwrite into cache data

cmd:loadread data from cacheif found, return data, else call prior action


layers

cmd:savecall prior actionwrite into cache data

cmd:loadread data from cacheif found, return data, else call prior action

insert into table name values data

select * from name where query


more data layers

validationpermissionsthrottling

custom logicmultiple databases

...


multiple databases

cmd:save, name:sessionsave data to redis

cmd:saveinsert into table name values data

when entity is a session:

all other entities:


fine-grained controleasy to extend

easy to customizeeasy to debug - there's no magic

Win


Micro-Services

deployerdispatchercontroller

Platform-as-a-Service


deployer

controller

dispatcher

app appapp

requestsstartstop

install

route

dashboard


controller actionsdash:install, app:detailssubmit cmd:install, app:details to message bus (deployer picks up)

dash:start, app:idsubmit cmd:start, app:id to message bus (dispatcher picks up)

dash:stop, app:idsubmit cmd:stop, app:id to message bus (dispatcher picks up)


deployer actionscmd:install, app:details

download app code to serverget route from app detailssubmit cmd:route, route:path, server:server to message bus (dispatcher picks up)


dispatcher actionscmd:routeadd route and server to local routing table

cmd:start, app:idstart routing requests to app

cmd:stop, app:idstop routing requests to app


controller, dispatcher, deployer are all in one app

install apps to localhostfocus on what, not how

Prototype


controller, dispatcher, deployer are separate processes

communicate via direct HTTPapps live on VMs

but ... no design changes!

Minimum ViableProduct


controller, dispatcher, deployer are many processes

communicate via a message busapps live anywhere

but ... no design changes!

Scale It


build now, scale later!easy refactoring

language independenceeasily observe and manage

Win


How do You Build Big Apps?


Design for ManyLanguages


Design forScale

(human + machine)Tuesday 13 August 2013

Design forHuman Brains


Thank You!@rjrodger

senecajs.org


Technology

The Seneca Pattern at EngineYard Distill 2013 Conference