Google AppEngine is an application platform that allows developers to build and host web applications in the cloud. It provides automatic scaling of web and worker instances, high availability, load balancing, and simple deployment. The platform handles low-level tasks like hardware provisioning and maintenance. However, applications are limited by the sandbox environment and certain features like file system access and sockets are not supported. Pricing is based on usage of resources like bandwidth, CPU time, and data storage. While deployment is easy, applications need to be designed specifically for the AppEngine platform to work within its constraints.

1. Google AppEngine
Paul Bakker

2. About me
Paul Bakker
• Trainer Info Support Hibernat
EJB 3
e
• NLJUG speaker JSF
Flex
• Java Magazine author Seam
Groovy
JavaFX
Grails
Spring

3. About Info Support
• Financieel gezond sinds oprichting 1986
• Focus op IT vakmanschap
• Brede en integrale dienstverlening
• Partnerships met o.a. Microsoft, IBM, NLJUG
• Vestigingen in Nederland en België
- 250+ medewerkers in Nederland
- 25 medewerkers in België

4. Presentation Goal
Introduction to
Developing
applications for
AppEngine

5. Outline AppEngine
Cloud Services
offerings Using
Introducing frameworks
AppEngine Pricing
Developing
and
deploying
Storing data

6. Clouds N’ stuff

7. Infrastructure
as a Service
Platform as a
Service
Software as a
Service

8. Infrastructure
as a Service
A virtual hardware platform
Full control of the operating system
Custom configuration of application servers

9. Infrastructure
as a Service
Pros
It’s just works like your old hardware
No development limitations
No lock-in
Cons
You still have to manage servers
No automatic scaling

10. Platform as a
Service
A virtual application server
No control of the operating system
Running in a sandbox

11. Platform as a
Service
Pros
No more server management
Easy deployment
Automatic scaling
Cons
Limited by the sandbox
Can’t run existing apps

12. Software as a
Service
Run an application from the cloud
Might extend the application using a
proprietary API

13. AppEngine
Intro

14. AppEngine architecture

15. Handling requests
Each application gets a free domain name
http://yourappname.appspot.com
You can add your own domain name
Each request has a 30 second timeout
Streaming responses are not supported

16. Scaling
JVMs are started on demand
on app startup
after inactivity
when upscaling
Starting a JVM causes a “loading request”
the app is loaded during that request

17. Loading request
optimization
Application startup time is now important
the app might be started after a request
Reduce the use of libraries
Prevent heavy initialization code
share data with multiple JVMs using
MemCache

18. The sandbox
You can’t
Write to the file system
Open sockets
Start threads
Invoke most System calls
Reflect on classes not belonging to the app
Use JRE classes not on the white list

19. Supported
Java Data Objects (JDO)
Java Persistence API (JPA)
Java Server Faces (JSF)
Java Server Pages (JSP) and JSTL
Java Servlet API 2.4
JavaBeans Activation Framework (JAF)
Java Architecture for XML Binding (JAXB)
JavaMail
XML processing APIs including DOM, SAX and XSLT

20. Not Supported
Enterprise Java Beans (EJB)
JAX-WS and JAX-RPC
JDBC
Java EE Connector Architecture (JCA)
Java Management Extensions (JMX)
Java Message Service (JMS)
Java Naming and Directory Interface (JNDI)
Remote Method Invocation (RMI)

21. Creating and
uploading an application

22. Storing Data

23. DataStore
Distributed architecture
Highly scalable
Not relational
Schemaless
Properties have one or more values

24. Sharded architecture
Row name Values
A [...]
B [...]
C [...]
Row name Values
D [...]
E [...]
F [...]
Row name Values
G [...]
H [...]
I [...]

25. Entity storage
Kind => table
Key => primary key
Entity Group => partition
Typed properties => columns
Kind Person
Entity Group /Person:Paul
Key /Person:Paul
name string: Paul Bakker
colleagues Key:/Speaker(68) Key:/Speaker(15)

26. Entity Groups
Entities are hierarchical
Useful for “owned” relations
a chapter can’t exist without a book
/Book(24)/Chapter(2)/Paragraph(3)

27. Queries
Supported filters
< less than
<= less than or equal to
= equal to
> greater than
>= greater than or equal to
!= not equal to

28. Indexes
Each query uses an index
One index for each combination of:
kind
filter property
operator
sort order

29. Index example
JPQL queries
select s from Speaker s order by s.firstname, s.lastname
select s from Speaker s WHERE s.firstname LIKE :firstname order by s.firstname, s.lastname
select s from Speaker s WHERE lastname LIKE :lastname order by s.lastname, s.firstname
Index configuration

30. Transactions
The DataStore is transactional
All DataStore write operations are atomic
Only a single Entity Group can be used
within a transaction
entities in the same group live physically
together

31. Transactions

32. Transactions
Begin transaction

33. Transactions
Begin transaction
Create new Speaker (/Speaker(1))

34. Transactions
Begin transaction
Create new Speaker (/Speaker(1))
Add Talk (/Speaker(1)/Talk(1))

35. Transactions
Begin transaction
Create new Speaker (/Speaker(1))
Add Talk (/Speaker(1)/Talk(1))
Add new Speaker (/Speaker(2))

36. Transactions
Begin transaction
Create new Speaker (/Speaker(1))
Add Talk (/Speaker(1)/Talk(1))
Add new Speaker (/Speaker(2))
Commit transaction

37. Transactions
Begin transaction
Create new Speaker (/Speaker(1))
Add Talk (/Speaker(1)/Talk(1))
Commit transaction
Begin transaction
Add new Speaker (/Speaker(2))
Commit transaction

38. Transaction Isolation
Within a transaction: Serializable
transactions are completely isolated
Outside a transaction: Read Committed
get() will only consist of committed data
queries are more subtle

39. Understand commits
A commit() consists of two milestones
1 changes to entities visible
2 changes to indexes visible
the entity is updated, but might not be
returned by a predicate query

40. Understand commits
bob.age == 18
Transaction 1
bob.age += 1
select ... where age = 18
Transaction 2

41. Understand commits
bob.age == 18
Transaction 1
bob.age += 1
select ... where age = 18
Transaction 2
bob is returned

42. Understand commits
bob.age == 18
Transaction 1
bob.age += 1
select ... where age = 18
Transaction 2
bob is returned
bob.age == 19

43. The low level API
JDBC like API
Work directly with untyped entities and
properties
Query using GQL

44. Creating entities

45. Queries

46. GQL
SELECT [* | __key__] FROM <kind>
[WHERE <condition> [AND <condition> ...]]
[ORDER BY <property> [ASC | DESC] [, <property> [ASC | DESC] ...]]
[LIMIT [<offset>,]<count>]
[OFFSET <offset>]
<condition> := <property> {< | <= | > | >= | = | != } <value>
<condition> := <property> IN <list>
<condition> := ANCESTOR IS <entity or key>

47. GQL

48. Setting up JPA
Add JPA and DataNucleus jars
Create persistence.xml
Configure post-compilation class
enhancement

49. Persistence Unit

50. EntityManagerFactory

51. Creating an Entity

52. JPA limitations
No “Joined” inheritance
No “Single Table” inheritance
would be technically possible
No many-to-many relationships
No join-queries
No aggregation queries
No polymorphic queries

53. Owned relationships
The “owned” entity only has meaning when
it’s parent exists
Key includes parent key
/Department(24)/Employee(2)

54. Owned relations

55. Owned relations

56. Polymorphic relations
Throws exception!

57. Using JPA

58. Unowned relations
No referential checks!

59. Unowned relations
Both entities can exist without the other
an employee and it’s colleagues
Cannot be used within the same
transaction

60. Loading collections

61. Many-to-many
GAE doesn’t support JPA many-to-many
Work around by mapping key collections

62. Unowned collections

63. Constraining pages
Uses Google Accounts
Require users to log-in
Require the admin role
admin == developer on GAE

64. Require to
login
Require
admin role

65. Login and logout
Login
Logout

66. Using Google Accounts

67. Services Mail
Users
Queus
MemCache
Blob Store
Cron Jobs

68. Mail service

69. Receiving mail
! Mail can be send to
somename@appid.appspotmail.com!
POST!
AppEngine! MyServlet!
/_ah/mail/address!

70. Cron Jobs
Tasks that run automatically on specific
times or intervals
sending a week report
nightly cleanup
Executing a job is invoking a URL

71. Configuring jobs
Configure job in WEB-INF/cron.xml

72. Cron syntax
every N (hours|mins|minutes)
("every"|ordinal) (days) ["of" (monthspec)] (time)
Examples
every 5 minutes
every 12 hours
2nd,third mon,wed,thu of march 17:00
every monday 09:00
1st monday of sep,oct,nov 17:00
every day 00:00

73. Cron jobs

74. Task Queues
Process asynchronous, parallel background
tasks
Modeled as web hooks
a request to a web hook is scheduled
the request handler is just like any other
user request
a web hook has data and code

75. Task queue use cases
Send multiple confirmation emails
each email is sent by a request to the
same task with different data
Place order
send confirmation email (task 1)
send notification to admin (task 2)

76. Adding tasks
/notification

77. Configuring queues
WEB-INF/queue.xml
rate: throttling task execution
bucket-size: “token-bucket” algorithm

78. Task Queues

79. Saving files
Store files up to 50 mb in the BlobStore
Upload by form POST
file is uploaded to the BlogStore
get a blob key in code
Serve file using blob key

80. Upload file

81. Serving files

82. Listing blobs

83. BlobStore

84. MemCache
Distributed in-memory cache
e.g. cache frequent queries
JCache API (JSR 107)
Low level API

85. Using a cache
Cache expires after 3600 miliseconds

86. Memcache

87. Frameworks
on AppEngine

88. Frameworks
A lot of frameworks work “mostly”
but you never know if/when it breaks...
JSF 1.2 e.g. RichFaces is not!
JSF 2 disable threads
Grails using a plugin
Weld multiple issues
JAX-WS
EJB
Spring some modules are not
JMS

89. Testing

90. Unit Testing
Easy out of container unit testing
In-memory DataService, MailService,
MemcacheService, TaskQueue,
AuthenticationService etc.

92. Setup
local
datastore

93. Create
datastore
instance

94. Use
datastore
API
directly

95. Using JPA

97. TaskQueue testing
(setup)

98. TaskQueue testing
(test)

99. Unit Testing

100. Costs

101. Quotas
Free Default Quota Billing Enabled Default Quota
Resource
Daily Limit Maximum Rate Daily Limit Maximum Rate
7,400 requests/ 43,000,000 30,000 requests/
Requests 1,300,000 requests
minute requests minute
Outgoing 56 megabytes/ 1 gigabyte free; 10 gigabytes/
Bandwidth (billable, 1 gigabyte 1,046 gigabytes
minute minute
includes HTTPS) maximum
Incoming 56 megabytes/ 1 gigabyte free; 10 gigabytes/
Bandwidth (billable, 1 gigabyte 1,046 gigabytes
minute minute
includes HTTPS) maximum
15 CPU-minutes/ 6.5 CPU-hours free; 72 CPU-minutes/
CPU Time (billable) 6.5 CPU-hours 1,729 CPU-hours
minute minute
maximum

102. Pricing
Resource Unit Unit cost
Outgoing
gigabytes $0.12
Bandwidth
Incoming
gigabytes $0.10
Bandwidth
CPU Time CPU hours $0.10
gigabytes per
Stored Data $0.15
month
Recipients
recipients $0.0001
Emailed

103. Setting a budget

104. The verdict
Deployment can’t get any
easier
Sandbox can be a show
stopper
Apps should be
developed specifically for
AppEngine

105. Google AppEngine
Paul Bakker