1

© 2010 VMware Inc. All rights reserved

Google AppEngine

Recommended Text:

Programming Google App Engine

Dan Sandersons O’Reilly

2

AppEngine

! Web application hosting environment !  Highly scalable !  Automatic scaling •  AppEngine allocates resources to the application as needed

!  Fault tolerant

3

Components

!  Run time environment •  Java

•  Python •  PHP

• Go

!  Datastore • Object database

!  Scalable services • URL Fetch

• Mail •  Image manipulation

•  Extensible Messaging and Presence Protocol (XMPP) •  Task queue (asynchronous processing)

4

Runtime Environment

!  Stateless •  Springs into existence to handle a request

• May go away after request is over • Requests routed independently to some server in infrastructure

!  Sandboxing • Read only access to local file system •  Limits the amount of resources per request

•  Memory and CPU time •  Application that use a lot of CPU of memory are throttled

• No new thread creation

• No direct networking • No awareness of other applications running on the same host

2

5

Eclipse Google Plugin

!  Create AppEngine projects !  Debug project locally !  Upload projects to AppEngine

6

Directory Structure

7

AppEngine Console

!  https://appengine.google.com/

8

Application Configuration

! war/WEB-INF/appengine-web.xml

!  AppEngine URL •  http://[{version}.]{appname}.appspot.com/

•  http://1.ece1779.appspot.com •  http://ece1779.appspot.com

3

9

Logging

!  AppEngine logs all requests • Data, time, client IP, URL, referring URL user-agent, HTTP status code

• CPU time, response size

!  Applications can also log events

10

Logging

!  Java log levels: FINEST, FINER, FINE, CONFIG, INFO, WARNING, SEVERE

!  Logging level configured in war/WEB-INF/logging.properties .level = INFO ClassName.level = ERROR

!  AppEngine log levels: debug, info, warning, error, critical finest, finer, fine, config -> debug severe -> error un caught exceptions -> critical

! Writes to stdout are logged at “info” level ! Writes to stderr are logged at “warning” level

11

Request Handling

!  Requests are short: 30 sec max.

12

Static File Configuration

!  Two kinds of files •  Static: deployed on static servers

• Resource: deployed on application servers

!  Default policy •  Static: all files in WAR except contents of WEB-INF and JSPs

• Resources: all files in WAR

!  Customize policy in war/WEB-INF/appengine-web.xml <resource-files>

<exclude path=“/images/**” /> <resource-files>

<static-files> <exclude path=“/**.xml” /> <include path=“sitemap.xml” expiration=“2d” />

</static-files>

4

13

Integration with Google Accounts

!  Possible to use Google Accounts to handle user authentication !  Can detect whether the current user has signed in !  Redirect the user to the appropriate sign-in page to sign in !  App can access the user's email address !  Detect whether the current user is an administrator •  Simplify implementation of admin-only areas of the app.

import com.google.appengine.api.users.User; import com.google.appengine.api.users.UserService; import com.google.appengine.api.users.UserServiceFactory;

UserService userService = UserServiceFactory.getUserService(); User user = userService.getCurrentUser(); user.getEmail(); user.getUserId();

14

Storage

!  AppEngine Datastore •  a NoSQL schemaless object datastore, with a query engine and atomic

transactions.

! Google Cloud SQL • Managed relational database

•  https://developers.google.com/cloud-sql/

! Google Cloud Storage •  Scalable, highly available storage service for objects and files up to terabytes

•  https://developers.google.com/storage/

15

Datastore

!  Highly scalable !  Fault tolerant !  Distributed !  Resembles a object database !  Data stored as entities !  Entity consists of: •  Kind

•  Similar to a RDB table, immutable

•  Key •  Immutable

•  Properties •  Different entities of the same kind may store different properties •  A property can store multiple values at once

16

Java Persistence API (JPA)

!  Standard Java API for persisting Java objects !  Supported by AppEngine Datastore !  Annotations define entity kind, id and which properties to persist •  By default JPA persists builtin Java types (e.g., String, Date) • @Basic persists a non-standard Java type property • @Transient marks property as non-persistent

5

17

Java Persistence API (JPA)

!  J2EE standard !  Supported by Google Datastore ! Mappings •  kinds -> classes

•  entities -> objects •  fields -> properties

!  Data types supported by either •  Primitive Java data type (e.g., String, Int) •  Application-defined data type (e.g., Preferences)

18

EntityManagerFactory

! Object that interacts with the Datastore

19

Saving an Entity

20

Fetching/Deleting an Entity

6

21

Security Configuration

!  Configured in war/WEB-INF/web.xml !  HTTPS

!  User authorization with Google Accounts •  <role-name> can be either * or admin

22

Frontend Performance

!  Can configure in management console !  Administration->Application Settings->Performance •  Frontend Instance Class

•  Idle instances •  # of idle instances kept in standby

•  Pending latency •  Latency before starting new instance to handle waiting requests

23

Backend Performance

!  Special App Engine instances !  Have no request deadlines, higher memory and CPU limits !  Persistent state across requests !  Started automatically !  Can run continously for long periods !  Individually addressable •  http://[instance].[backend_name].[your_app_id].appspot.com

24

Bankend Configuration

! war/WEB-INF/backends.xml

!  Administer •  AppEngine management console

•  appcfg.sh command line tool (part of the Java SDK)