google appengine (gae/j) - introduction and overview from a java guy

Dr. Max Völkel, Calpano 1

You know Java, but what is AppEngine? In this session Max will walk you from a brief introducAon of Servlets to an overview of the Google AppEngine. We learn about the basics such as the data store – which is quite different from SQL -‐, applicaAon versions, back-‐ends, scheduler, instances and logging. Services such as mail, url fetch, task queue are also explained. Since we use GAE/J since 2010 in Calpano we also talk about costs and experience in pracAce.

Poll §  Language? §  Java? §  AppEngine? §  Servlets?

GDG Karlsruhe DevFest 2012 | Dr. Max Völkel | Calpano.com 2

Do you know Servlets? §  HttpServlet

•  void doGet( HttpServletRequest req, "HttpServletResponse res);"

•  void doPost(…)"§  HttpServletRequest

•  get Header(…), get InputStream(...)"§  HttpServletResponse

•  set Header(…), getOutputStream(...)" See: http://java.sun.com/products/servlet/, AppEngine supports version 2.5"


AppEngine is a Servlet Container

§  Servlet Container runs a Web Application Archive (WAR) •  Class files •  Static resources •  web.xml"

§  In AppEngine also: •  appengine-web.xml, queue.xml, cron.xml, backends.xml, indexes.xml, …


AppEngine Architecture�Java/Python/Go

§  Running Code §  Storing Data

•  JVM •  Memcache •  Data store (Old vs. High

Replication) §  Connect to the outside world

•  Mail (Incoming, Outgoing) •  Urlfetch

§  Delay or schedule work •  Taskqueue •  Cron

§  More helper services •  Images •  Users


Servlet Container

JVM

Data Store Memcache Images

HTTP, Incoming Mail, Cron, Taskqueue

Urlfetch, Outgoing Mail, Taskqueue

Hello AppEngine §  Typical first test: •  Register, Verify mobile number via SMS •  Create new app “helloworld”

•  http://helloworld.appspot.com

§  Next step: •  Buy domain name •  Configure …


1.  Appspot.com > Create App

2.  Go to “Apps for your Domain”�https://www.google.com/a/calpano.com

3.  Organization & Users > Create user�! Only those can send emails

4.  Domain Settings > �Domain names > �Add domain name or alias >

5.  Go to appspot.com and “Add Domain”


Application Versions §  http://{version}.{appid}.appspot.com"§  http://{appid].appspot.com �à main version (Selected in Dashboard)

§  All versions •  Share the same datastore, memcache (!) •  Different logs, stats, instances


Running Code §  Java 6 VM (experimental Java 7) §  No Files (only read the ones you put in your .war) §  Explicit whitelist which Java classes are allowed (many!)

•  https://developers.google.com/appengine/docs/java/jrewhitelist

§  F1: 8 cent/hour •  128MB memory (!), •  600MHz CPU

§  F2 = F1 * 2; F4 = F1 * 4 §  ! Servlet response max. time is 60 seconds


Storing Data §  JVM •  Great when “always on”

§  Memcache •  Really just a cache

§  Data store •  Old: Master-Slave (2 data centers) •  High Replication (3 data centers)


Connect to the outside world §  Mail •  Incoming

•  Send as a servlet request •  Outgoing

•  Via Java Mail API, only some headers used •  ! Bounce processing

•  http://code.google.com/p/googleappengine/issues/detail?id=1800

§  Urlfetch •  ! Calling Twitter API etc.


Delay or schedule work §  Taskqueue Queue queue = QueueFactory.getDefaultQueue();!queue.add(TaskOptions.Builder.withDefaults()!.payload(task));!

•  Task is a DeferredTask (has a run() method) •  Very quick to enqueue task •  Task queue service fires requests as

HttpRequests at defined rates, unwraps task, runs it

•  Max runtime: 10 minutes §  Cron •  Scheduled GET-requests at defined urls


More helper services §  Images •  Looks like a subset of ImageMagick

§  Users •  Log in via Google Account


Where is a request going? Typical setup §  DNS lookup: CNAME or A-record to Google §  GAE scheduler: •  Request queue for your app •  Boot new instance? Takes ca. 10-30 seconds.

§  On instance: •  Run WAR, •  Run servlet


Instances


Time is Money. What time? §  Free vs. Payment enabled §  Quotas •  Usage – Free = Billable à Pay •  Resource quota à Fair use limit à Error page

§  Data store •  See also

http://blog.xam.de/2011/11/analysis-of-datastore-operation-cost.html

§  Instance hours •  Usage (code time * complexity + 15 min) •  What???


Real time vs. API time

§  CPU-intensive code is more expensive •  Is magically speed-up by AppEngine


The Scheduler Appspot > App Settings > Performance


Appstats


More stuff §  Backends •  Requests run for hours (or even days?)

§  Logging •  Java.util.logging runs fine

§  Blobstore §  Channel ~ like websockets §  XMPP §  Remote API: •  Call services remotely


Practical Tips on Datastore §  Don’t use JDO abstraction •  Leaky abstraction anyway

§  Low-level API quite easy •  Objectify (open source) makes using it nice •  Xydra.org adds versioning/synchronisation


Real-World Experiences §  Xydra §  Calpano.com §  SonicMetrics.com


Servlet Container

JVM




When to use AppEngine? §  Best: Spikes in demand §  OK: Outsource server management


Where to learn more? §  Next talk from Florian Krupicka on

Continuous Integration with AppEngine and Maven

§  Google webseits – Docu, JavaDocs, Articles, §  Stackoverflow – Googles official developer

support moved there §  Books •  Programming Google AppEngine – was OK when

it came out, but now too outdated §  Book a workshop from Calpano Consulting J


Dr. Max Völkel

25

Servlet Container

JVM




GDG Karlsruhe DevFest 2012 | Dr. Max Völkel | Calpano.com

Contact Information §  Dr. Max Völkel §  [email protected] §  +49 171 8359678

§  www.Calpano.com


google appengine (gae/j) - introduction and overview from a java guy

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