GAE Architecture

Front-End: Load Balancing &
Request Forwarding
 Static Files: Serving static files,
i.e. images/CSS/JS
 AppServer: Process requests &
call services
 Datastore: central place for data
persistence

Because must run in sandbox for app security (other apps dont hack into yours)

>>no local file, no system call, no socket connection

<< these services help accommodate for the loss of this

Java

how Java concepts map down to GAE

Datastore API

• Storing data and manipulation
• Based on Bigtable
• Not a relational database
• GQL (Google Query Language)
• For Java options - use JDO or JPA or native Google App Engine API
• Package com.google.appengine.api.datastore

Memcache

• Faster than Datastore
• Storage on memory rather on disk
• Arbitrary key-value pair mapping
• implements JCache interface
• ?(1) MB limit per entry
• Free quota (varies --see current rules) around 8.6M/day, 800 request/sec
• Package com.google.appengine.api.memcache

User Service

• Using google accounts for authentication
• @gmail.com address
• Apps for Domain
• Admin Privileges
• Package com.google.appengine.api.users

URLFetch Service

• Alternative as no Sockets
• Load external URL
• Asynchronous support
• HTTP/HTTPS
• Max 10 second response (see current stats http://code.google.com/appengine/docs/java/urlfetch/)
• Max 1MB data (see current stats http://code.google.com/appengine/docs/java/urlfetch/)
• Package com.google.appengine.api.urlfetch
  

Mail Service

• sending mail from your application
• Package com.google.appengine.api.mail
  • com.google.appengine.api.datastore
  

XMPP Service

• sending/receiving XMPP-compatible instant messages

Task Queues

• for invoking background processes

Images

• for image manipulation
• uses Picasa
• Package com.google.appengine.api.images
  

Cron Jobs

• scheduled tasks on defined time