Using Amazon SimpleDB
with Rails
Martin Rehfeld
@ RUG-B 07-Feb-2008

Remember?
AWS Rails Scenario
}
EC2 S3
Web Static
Server Content
Application
Server
memcached,
backgrounDRb,
Code

...
SQL

HOW
TO
GET A
PERSIS
Database DB?
TENT

limited
beta
Amazon SimpleDB
• Database web service advertised as
• Simple, Flexible, Scalable, Fast,
Reliable, Inexpensive
• No RDBMS: no SQL, no joins, no schema,
no referential integrity, no transactions
• HTTP-Interface
• Pay per use:
• $0.14 per Machine Hour consumed
• $0.10-0.18 per GB - data transfer
• $1.50 per GB-month storage

Amazon SimpleDB
Common Terms
• Domain: SimpleDB
storage container ~ table
• Item: my domain A
attributes
~ table rows accessed by
ID ~ primary key }
items
• Attribute:
(multiple) values
~ table columns; every item
may have a different set of up
to 256 attributes my domain B
• Value: ...
each Attribute may have
multiple Values, always
varchar(1024)[]

SimpleDB @
no code
no code
no code
no code
no code
no code
no code
(amazon_sdb)
rich API*
simply working!
*) defect release 0.6.5 when evaluated, but newer release available (not re-tested yet)

Amazon SimpleDB API
• Domain level
• CREATE, LIST, DELETE
• Item level
• GET, PUT, DELETE attributes with values
• QUERY* for unordered item IDs by
attribute values within one domain
*) lexicographical =, !=, <, > <=, >=, STARTS-WITH,
AND, OR, NOT, INTERSECTION / UNION
• Beware: Eventual Consistency Approach!

Almost
RESTful

Mapping RESTful URLs
HTTP/REST SimpleDB
GET
/domain?query QUERY
GET
/domain/itemID GET ATTRIBUTES
POST
/domain/itemID PUT ATTRIBUTES
PUT
/domain/itemID PUT ATTRIBUTES
(replace)
DELETE
/domain/itemID DELETE ATTRIBUTES

Mapping RESTful URLs
Emulating multiple resources in one domain via _resource attribute
HTTP/REST SimpleDB
GET
/domain/resource?query QUERY
GET
/domain/resource/itemID GET ATTRIBUTES
POST
/domain/resource/itemID PUT ATTRIBUTES
PUT
/domain/resource/itemID PUT ATTRIBUTES
(replace)
DELETE
/domain/resource/itemID DELETE ATTRIBUTES

A Bridge to Rails
ActiveResource
„Rails XML“
HTTP/REST
?
AWS
SDB Proxy
Server*
„AWS XML“
HTTP/SDB API
SimpleDB
*) http://inside.glnetworks.de/2008/01/20/bridging-rails-to-amazon-simpledb-using-activeresource/

AWS SDB Proxy Plugin I
• Install aws-sdb gem
gem install aws-sdb
• Install aws_sdb_proxy plugin:
script/plugin install http://rug-b.rubyforge.org/svn/aws_sdb_proxy
• Configure config/aws_sdb_proxy.yml
development:
aws_access_key_id: <your amazon aws key>
aws_secret_access_key: <your amazon aws secret key>
port: 8888
• Create new domain on Amazon SimpleDB
rake aws_sdb:create_domain DOMAIN=ActiveResourceStore
• Start AWS SDB Proxy
rake aws_sdb:start_proxy_in_foreground

AWS SDB Proxy Plugin II
• Create demo ActiveResource model
class Post < ActiveResource::Base
self.site = \"http://localhost:8888\"
self.prefix = \"/ActiveResourceStore/\"
end
• Testdrive in script/console
>> p = Post.create(:title => 'My first SimpleDB post')
=> #<Post:0x198ceec @prefix_options={}, @attributes={...}>
>> p.body = 'Content is king'
=> \"Content is king\"
>> p.save
=> true
>> Post.find(:first, :params => { :title => 'My first SimpleDB post' })
=> #<Post:0x18efef8 @prefix_options={}, @attributes={...}>

Vision: Fully Virtualized
Scalable Stack...
• Building blocks for AWS-only web app
deployment:
• Static assets/content in S3
• As many app servers as needed on EC2
• Structured data persisted in SimpleDB
• All client/server interactions via SQS
Note: XmlHttpRequest cross-site restrictions must be examined

Q &A
! Martin Rehfeld
http://inside.glnetworks.de
martin.rehfeld@glnetworks.de