The Seneca Pattern at EngineYard Distill 2013 Conference

How do You Build
Big Apps?
@rjrodger
senecajs.org
Tuesday 13 August 2013

Technical
Debt

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

You Must take on
Technical Debt
or You Will Die

Sometimes,
it Happens
Anyway

NTSC 1941 Standard:
Black+White only
Signal encodes Brightness
Each Channel gets 6Mhz
Happy Days!

Color Television
Three Colors: Red, Green, Blue
Each Color needs 3Mhz
You only have 6Mhz
and you need 9Mhz!
Technical Debt FTW

You can't Break the
old Black+White TVs

We must send the old brightness signal
White Light =
30% Red
59% Green
11% Blue
Send White, Red and Blue

You need to embed the
color signals inside
the brightness signal

Color TV circuits are
more complicated
than they should be.

How do you Reduce
Technical Debt?

Longer and
more detailed
Specifications!

Better Languages
Better Mental Models

How did the
Romans do
Long Division?

LXXII MMMDCXII
L rem XII

How did the
Romans do
Addition?

1. Normalize: IV → IIII
2. Concatenate: IIII + XI → IIIIXI
3. Sort, descending: IIIIXI → XIIIII
4. Reduce: XIIIII → XV
IV + XI = ?

How did the
Romans do
Subtraction?

1. Normalize: XXIV → XXIIII
2. Eliminate: XXIIII - XV → XIIII - V
3. Expand: XIIII - V → VIIIIIIIII - V
4. Repeat 2 and 3 until no moves left
5. Reduce: IIIIIIIII → IX
XXIV - XV = ?

How did the
Romans do
Multiplication?

III → 3
VI → 6 → 110
III × VI = ?
3 × 001 × 0 = 0
3 × 010 × 1 = 6
3 × 100 × 1 = 12
18
bit shifting

How did the
Romans do
Division?

they didn't

Roman Numerals
have
Technical Debt

Positional Number
Systems make us
Smarter

Mental Models
for Code

Procedural
Functional
Object-Oriented
Logic

Let's Experiment

Stand up.
Everybody.

Is this a car?

YES NO
Stay standing Sit down
And stay down!

Objects are
Roman Numerals

Objects break as
system complexity
grows

The need for design
"patterns" is telling
you something

Procedural code
tends to
Spaghetti

Functional and Logic
are
More Powerful

What
Happened?
Why didn't they
Win?

Technical Debt

What do we
Need?

A Better
Mental Model

Easy to Learn
Easy to Scale (humans)
Easy to Scale (machines)
Easy to Implement
Easy to build a Mental Model
Does not have to achieve
Very Large Scale

We need Models
that Work for
Human Brains

Why is
Ruby on Rails
Popular?

Opinionated
==
Shared Mental Model

Ruby on Rails
Model is an
Accident of History

Let's Design a
Model!

What does a Programmer do?
Self-contained Algorithms
Procedural Business Logic
Fitting it all Together

Fitting it all Together
is
the Hard Part

What are Humans
Good 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 Matching

Why is Pattern
Matching
Such a Win?

We are Pattern Matchers
It scales for humans and machines
Works without needing context

Why do I Care?

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

Lucius Annaeus Seneca

The Seneca
Strategy

Embrace
Micro-Services

Lots of Little Processes
Do one thing, and do it Well
Communicate with Messages

Pattern Match on
Messages

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

"Send Tweet"
Acted on by Tweet Service
Example
{
command:"tweet"
author:"@rjrodger"
status:"Distill Rocks!"
}

Tweet Service
If 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 Language

Keep it Small
Die and restart on Errors
Report your status

Level Up The
Pattern Matching

Patterns map to
Actions

cmd:drive
start engine, and go!
cmd:drive, type:hover
turn on anti-gravity
start engine and go!
Example

Two Rules to make this Unique
1. More properties always wins
2. Check properties alphabetically

cmd:drive
cmd:drive,
type:hover
Mapping
cmd: drive
type: wheel
speed: 50
cmd: drive
type: hover
speed: 100

One More Thing

When you add a pattern:
If the pattern Already Exists,
Keep the Old Action,
so you can use it
inside the New Action

cmd:drive
start engine, and go!
cmd:drive
call prior action
set 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:content
cmd:publish, post:id
cmd:redact, post:id
cmd:homepage
cmd:comment, post:id,
comment:comment

action, not abstraction
easy to learn
easy to modify
easy to maintain
self-documenting
Win

the actions are
Data Layer
cmd:save, name:entity
cmd:load, name:entity
cmd:list, name:entity
cmd: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:save
insert into table name values data
cmd:load
select * from name where query

add caching
cmd:save
call prior action
write into cache data
cmd:load
read data from cache
if found, return data, else call prior action

layers
cmd:save
call prior action
write into cache data
cmd:load
read data from cache
if found, return data, else call prior action
select * from name where query

more data layers
validation
permissions
throttling
custom logic
multiple databases
...

multiple databases
cmd:save, name:session
save data to redis
cmd:save
when entity is a session:
all other entities:

ﬁne-grained control
easy to extend
easy to customize
easy to debug - there's no magic
Win

Micro-Services
deployer
dispatcher
controller
Platform-as-a-Service

deployer
controller
dispatcher
app appapp
requests
start
stop
install
route
dashboard

controller actions
dash:install, app:details
submit cmd:install, app:details
to message bus (deployer picks up)
dash:start, app:id
submit cmd:start, app:id
to message bus (dispatcher picks up)
dash:stop, app:id
submit cmd:stop, app:id

deployer actions
cmd:install, app:details
download app code to server
get route from app details
submit cmd:route, route:path, server:server

dispatcher actions
cmd:route
add route and server to local routing table
cmd:start, app:id
start routing requests to app
cmd:stop, app:id
stop routing requests to app

controller, dispatcher, deployer
are all in one app
install apps to localhost
focus on what, not how
Prototype

are separate processes
communicate via direct HTTP
apps live on VMs
but ... no design changes!
Minimum Viable
Product

are many processes
communicate via a message bus
apps live anywhere
but ... no design changes!
Scale It

build now, scale later!
easy refactoring
language independence
easily observe and manage
Win

How do You Build
Big Apps?

Design for Many
Languages

Design for
Scale
(human + machine)

Design for
Human Brains

Thank You!
@rjrodger
senecajs.org

The Seneca Pattern at EngineYard Distill 2013 Conference

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