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Lessons from developing an Iphone App + Server backend Sujee Maniyam Feb 2010.

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Presentation on theme: "Lessons from developing an Iphone App + Server backend Sujee Maniyam Feb 2010."— Presentation transcript:

1 Lessons from developing an Iphone App + Server backend Sujee Maniyam Feb 2010

2 Quiz PRIZE! Where was this picture taken?


4 My Background Developer (enterprise, web) Java / Php / Ruby / obj-C First iphone app (Apr 2009)

5 Target Audience Iphone app developers Server backend developers for mobile apps Expert level: Beginner - Intermediate

6 Why Client-Server Apps? Some apps run fine on the device disconnected (Tips calculator) “I think” majority of SMART apps in the future will have a server backend Some cool apps – Amazon – Yelp – Red Laser – Countless games

7 Server Backend gives you… A community (games, social interactions) Push Notification Heavy computational lifting (image recognition) Up-to date data (bar code scanners) ‘collective intelligence’ (most popular item today is…)

8 My App: DiscountsForMe Shows member benefits Based on location V2.0 in app store Memberships: – Public radio (KQED, WHYY) – Bank of America card – AARP – More…

9 Architecture Server ( serves data Server is Rails app Iphone app talks to the server

10 Web App / Mobile App ? What should server side code support? Are you adding mobile support for an existing web-app? Just mobile platform? (simpler ??) Hybrid (web + mobile)  more work – DiscountsForMe is a hybrid app

11 1) Connectivity : Simple Start First cut : App made three server calls at startup – ping() – Get_X() – Get_Y() Simulator Iphone over Wi-fi Iphone over 3G LAG-TIME is a problem

12 Connectivity : Minimize Lag Time Noticeable lag time over 3G/Edge Reducing lag time – Show cached data – Download in background – Condense network calls (especially if the user is waiting for data) So, condensed call becomes – Get_X() – Get_Y()  get_X_Y()

13 Iphone Connectivity BIG LESSON 1 : – Test on IPHONE (not just simulator) – Test with WiFi OFF! (3G can be slow to connect, EDGE even worse) – You may need to reorganize the logic to improve response time (I had to) LESSON 2 – Test in AirPlane Mode (all RADIOS off) (a frequent reason network apps are rejected )

14 Network setup – WIFI Home network over WIFI Run local server on laptop Iphone + Simulator can connect just fine

15 Setup for 3G

16 Network Setup for 3G Need a public IP Use a hosted server Or use your cable modem public-IP and have your router do port-forwarding DYNDNS :

17 2) Talking to Server : Format Choices : XML, JSON, other (csv, binary – protobuf/thift) JSON smaller size than XML (50% less) Json : use TouchJSON library JSON String  Touch Json  NSDictionary (yay!) XML : NSXML(sdk) / TouchXML / KissXML iphone/ iphone/ Rails makes it real easy to send Json/xml – Some_obj.to_json – Some_obj.to_xml

18 Keeping it small Trim objects – No need to send all attributes – Active records have extra attributes (created_at, updated_at..etc) Example: # specify attributes to serialize obj.to_json(:only => [:name, :age]) # combine other my_response = {} my_response[:book_name] = my_response[:author_name] = render(:json => my_response.to_json()) - Compress (zip) response

19 GET vs POST iPhone SDK has a simple switch to control GET / POST What is the difference in Rails? – Post requests have ‘authenticity token’ for cookie based sessions – Use DB based sessions or turn off authenticity- protection

20 Agenda Connectivity Data format  Secure Data transfer UDIDs, Keys, analytics Controlling app from server

21 Secure Data Transfer Plain HTTP is fine most of the time If you want to secure data – Symmetric key encryption (shared ‘seckr3t’ key on Iphone app and server) – Public-private key encryption (e.g. SSH) : private key on server, public key on iphone – Enter : HTTPS

22 Secure data transfer : httpS SSL is ‘good enough’ for most of us Get a proper SSL certificate ($30). Self-signed certs don’t work by default Beware connection time is a little longer for httpS Verify your ssl certificate is installed properly


24 Verify SSL Cert…

25 Break & Quiz

26 Agenda Connectivity Data format Secure Data transfer  UDIDs, Keys, multiple versions, analytics Controlling app from server

27 What do I send to the server? Think about including – UDID (device id) – And a Key (compiled within the app) ey=yyyy ey=yyyy Why?

28 Unique Device ID (UDID) Each iphone has a unique ID, etched in hardware (just like MAC address) Your app can send UDID with each request Uses – metrics on app usage – Easy account creation (no signup)

29 Identify a User (Device) UDID can help you ‘auto –create’ accounts on server – Eg. High scores of games Allow users to create a custom user name later Beware of a user using multiple devices (multiple UDIDs)

30 Metrics Client Side metrics Server side metrics

31 Client Side Metrics – Code embedded in your iphone app – Usage, Users (new, repeat), session length – Few companies (Flurry, Pinch Media..etc) – Pretty easy to integrate – Nice dashboards – Free! (mostly)

32 Metrics : Client Side

33 Server Side Metrics – why? – Some things are easily measured on server side – ‘collective intelligence’ Popular discounts – Security audits Isolating an IP-address doing too many requests / scraping – Easy to extract data / graphs..etc – Needs a bit of work on your side

34 Sample Server Side log data Device_id : iphone, android, web, Location Ip_address Response_time Response_data_size Client_key Created_at Updated_at

35 Server Side Metric : Time To Serve Want to measure the time spent on each request use around_filter in Controller class MyController around_filter :log_access, :only => [:get_A]

36 Response Time … def log_access start_time = yield end_time = elapsed = ((end_time - start_time)*1000.0).to_int End

37 Server side Metric 2) Response Size def log_access start_time = yield end_time = elapsed = ((end_time - start_time)*1000.0).to_int response_data_size = response.body.length End

38 Response Time Chart Time (ms)

39 Response Size Chart Response size (kbytes)

40 Access keys Keys are random, ‘sekret’ strings compiled into the iphone app Sample key = “iphone_v1.0_xklajdfoi2” (human readable + ‘hard to guess’) Start using ‘access keys’ from day-1 Each request to server must have a valid key Uses – Easy to control client access (Prevent scraping, DOS..etc) – Monitoring (what versions are being used) – Support multiple versions, easy upgrade

41 Access Keys In controller: @@keys = [ "iphone_v0.0_foobar”, "iphone_v1.0_afajiu”, "iphone_v2.0_fi98d”, "iphone_v2.0_plus_fsafa”, "android_v1.0_fasjlkuo” ] @@keys_premium = ["iphone_v2.0_plus_fsfa"]

42 Supporting multiple versions May be supporting 2-3 client versions at a time (users don’t always run the latest) Keep old ‘API’ around, build-out new API if (is_v2_or_later(key)) { do something } else {do some thing else} This can get convoluted (see next page…)

43 Supporting multiple clients…

44 Supporting Multiple Clients… Have different controllers handle different client versions #define SERVER @”” #define SERVER @””” Make sure to avoid code duplication Plan-B : End-of-life If ( ! is_supported_version(key)) { send_msg(“please upgrade”); }

45 Server side : keeping it secure Make sure ‘secret stuff’ doesn’t get logged in log-files In Rails : class Mobile::MobileController < ApplicationController filter_parameter_logging [:key, :uid] end Output: Processing IphoneController#get_memberships_and_discounts (for at 2009-07-02 16:07:41) [POST] Session ID: 126e5a73742f92f85c1158ea63fd960a Parameters: {"loc"=>"39.282440,-76.765693", "action"=>"get_memberships_and_discounts", "uid"=>”[FILTERED]", "controller"=>"mobile/iphone", "dist"=>"25", "mems"=>"", "key"=>"[FILTERED]"}

46 Example : Controllers MobileController – IPhoneController < MobileController – AndroidController < MobileController Most of the shared logic in ‘MobileController’ Sample iPhone controller Class IphoneController < MobileController def client_type_id 3 end end

47 Example … Class MobileController @@valid_keys = [……] def ping to_ret = {} begin validate to_ret[:status] = “OK” rescue to_ret[:error] = $1.message end render (:json => to_ret.to_json) end

48 Example … Def validate #verify the key if (params[:key].blank?) raise DiscountsError, "dude, where is my key?" end if (params[:uid].blank?) raise DiscountsError, "dude, who are you?" end unless (@@valid_keys.has_key?(params[:key])) raise DiscountsError, "un supported version, please upgrade" end

49 Controlling app behavior from Server

50 Control … Apps changes are not easy to ‘get out’ – Approval process takes time – Users may not upgrade to latest version Server changes are under your control and easy to deploy So build in control-switches in the app, that can be directed from server

51 Control… One example: should display ads? – show_ads : {none | admob | tapjoy} Alert Messages: – “try our new version that has cool feature XYZ”

52 Server Logistics Choosing a hosting plan Deploy monitoring

53 Hosting Shared hosting is fine, but others might swamp your DB, CPU..etc If you can, get a VPS (Virtual Private Server) – Plans start from $20 / month (SliceHost, Hosting- Rails..etc) – You have full ROOT access to the server (install packages, run CRON jobs..etc) EC2 is great also (for testing, scaling)

54 Server : When to get it Don’t wait till TESTING phase! Get it from DAY-1, WEEK-1 Can use DNS services like DYNDNS to test on your own workstation, during development Work on easy deploy scripts – Capistrano – Or rsync

55 Monitoring So you know when your server is down Pingdom / CloudKick

56 Other Resources backend-servers by Ramin Firoozye backend-servers Restful web services

57 Thanks! Sujee Maniyam – – Questions?

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