CouchApps: Requiem for Accidental Complexity

CouchApps: Requiem for Accidental Complexity

Federico Galassi Giordano Scalzo

We have a problem...

Writing software is really hard...

A little bit of history

It wasn’t easy

A little bit better

Something happened

A different way of programming

DataBusiness Logic + Presentation

Two tiers architecture

DataBusiness LogicPresentation

Three tiers architecture

Tim Berners Lee invented the world wide web

ModelView+

Thin client

Controller

Three tiers internet style

Evolution ofMVC Web App

Browser is a thin client

Talking to asmart server

It all starts withan HTTP request

GET / HTTP/1.1Host: example.org

It hits theController

Web server parses itController

Controller

Dispatch tofront controller

Controller

Routing

Controller

Custom action

Gets datafrom Model

Query onmodel objects

Model

ORM fits into SQLModel

Hits a RDBMSModel

Populates aView

Template engineView

HTML back tothe server

View

HTTP/1.1 200 OK

HTML back tothe client

Model

View

Controller

That’s MVC

A little bit old school

We love AJAX speed

Model

View

Just need an API

Json View

Api ActionController

And somejavascript on client

Model

View Json View

Api ActionController

Javascript View

Niceone ring to rule ‘em all

Nocontraindications ?

Accidentalcomplexity

Every changetouches the server

Hard to scale

We mustadd another

serveeeeerrrr

Last technology cycleVisib

ility

maturity

technologytrigger

peak  ofinflated

expectation

disillusionment

productivity

obsolescence

MVCWE WERE HERE

Last technology cycleVisib

ility

maturity

technologytrigger

peak  ofinflated

expectation

disillusionment

productivity

obsolescence

NOW HERE

Last technology cycleVisib

ility

maturity

technologytrigger

peak  ofinflated

expectation

disillusionment

productivity

obsolescence

IF YOU’REAT THIS CONFYOU MAY BE

ALREADY HERE

Visib

ility

maturity

?

Next technology to save us?

Visib

ility

maturity

It’s a cyclebut we know one thing ...

Specializationis

Good

Very opinionateddocument DB

Very good forsome problems

A document DB{        "company":  "CleanCode",        "members":  [                {  "name":  "Gabriele  Lana",  "role":  "software  craftsman"},                {  "name":  "Federico  Galassi",  "role":  "software  craftsman"},                {  "name":  "Giordano  Scalzo",  "role":  "software  craftsman"}        ]}

Self contained data

NO JOINS

Schema-less data

EVOLVE YOUR DATA

{

"id": 1,

"day": 20100123,

"checkout": 100

}

{

"id": 2,

"day": 20100123,

"checkout": 42

}

{

"id": 3,

"day": 20100123,

"checkout": 215

}

{

"id": 4,

"day": 20100123,

"checkout": 73

}

100 42 215 73

Reduce: sum(checkouts)

142 288

430

IncrementalMap/Reduce

Map

Reduce

Re-reduce

Multi-VersionConcurrency Control

Crash-onlyarchitecture

lucky by design

A distributed DB

Eventualconsistency

Incremental replication

Automatic conflict resolution

Built of the Web“Django may be built for the Web, but CouchDB is built of the Web. I’ve never seen software that so completely embraces the philosophies behind HTTP.”

Jacob Kaplan-MossCo-creator of Django

Restful APIGET / Returns  MOTD

GET /_all_dbs List  of  databases

POST /_restart Restart  the  server

GET /_log Tail  of  the  server’s  log

GET /_config Entire  server  config

GET /_config/<section>/<key> Single  config  value

PUT /_config/<section>/<key> Set  a  single  config  value

GET /<db> Database  info

PUT /<db> Create  new  database

DELETE /<db> Delete  database

GET /<db>/<doc> Latest  revision  of  the  document

PUT /<db>/<doc> Insert  a  new  revision  of  the  document

... and everything else

Javascript toprogram

//  MAPfunction(doc)  {    if(doc.date  &&  doc.title)  {        emit(doc.date,  doc.title);    }}

JSON toexchange data

{    "_id":"hello-­‐world",    "_rev":"43FBA4E7AB",

   "title":"Hello  World",    "body":"Well  hello  and  welcome  to  my  new  blog...",    "date":"2009/01/15  15:52:20"}

Applicationsare

documents

Replicationas

deploy

A modern web application server

CouchApps arejavascript and html5applications served

directly from CouchDB

Model

View Json View

Api ActionController

Javascript View

Problem

Javascript View

Simple Solution

HTTP

Experiment:5 minutes comet chat

The couchapp tool

Generate the app

Configure the app

Deploy the app

That’s it

That’s it

User can post a message

Add form elements

On click POST message to couch

User can post a message

User can post a message

Yes!

User gets a stream of messages

Add messages container

User gets a stream of messages

User gets a stream of messages

Yes!

Validation?

Authentication?

Create a user

Authentication?

Add Form Elements

Authentication?

HTTP Basic Auth

Authentication?

If it goes wrong

Authentication?

Check sender is the authenticated user

Authentication?

{ sender: “whitehouse” } // spoofing

Authentication?

Yes!

Authentication?

BASIC HTTP ?????

No SSLYes cookie auth via _session api

UGLY URLS ?????

Rewrites and Virtual hosts

Easy eh?

But it’s not that ring

Very good forCRUD/small/simple

web

federico.galassi@cleancode.it giordano.scalzo@cleancode.ittwitter.com/giordanoscalzotwitter.com/federicogalassi

slideshare.net/fgalassi slideshare.net/giordano