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1. Closer to "Big Switch" idea plug and play.
Why Port to AppEngine?
2. Cheaper vs EC2 costsWhy Port to AppEngine?
Basic EC2 instance: ~ $60/month
AppEngineJava: low usage is FREE
3. Simpler development cycle
Just upload code and go!
Why Port to AppEngine?
Amazon feels like this....
Why Port to AppEngine?
Google is like this...
Toaster with wall socket
Why Port to AppEngine?
The Application
HTML & Javascript coded with GWT (Google Web Toolkit)
Description
Server
Java Servlets
Amazon SimpleDB for database
Amazon S3 for metadata and content storage
Client UI
Web page text and image annotation for research and scholarshoip.
30 second timeout
No threads
No file system writes
No sockets
AppEngine Limitations
more details:http://code.google.com/appengine/docs/java/runtime.html
No long running apps, e.g. genetic algorithm, no streaming.
Servlet cannot spawn threads (impacts SimpleDB)
Impacts on libraries
All writes must be to persistance storage, including log files
AppEngine Limitations
AppEngineJava != Java
Components
Works out of the box ... ...but project structure differences are enough to drive you a little crazy
GWT (Google Web Toolkit) - Eclipse plugin
Standard GWT project layout
Standard GWT project layout
Which means the relative path to the image is direct, e.g: DOM.setStyleAttribute(widget.getElement(), "backgroundImage", "url(image/myimage.jpg)");
AppEngine project layout
AppEngine project layout
Which means the relative path to the image starts from a higher directory e.g: DOM.setStyleAttribute(widget.getElement(), "backgroundImage", "url(../image/myimage.jpg)");
Therefore you will likely have to ensure that all resource strings, in code and CSS files are modified for this new structure.
AppEngine project layout
src/com/cloud/demo/MY_APPENGINE_PROJECT.gwt.xml
AppEngine project layout
WEB-INF/web.xml
Configuration hell. Can be very tiresome to ensure all the parts are correct. It may be easier to import the code into a new base project to save the effort.
AppEngine project layout
war/MY_APPENGINE_PROJECT.html
Configuration hell. Can be very tiresome to ensure all the parts are correct. It may be easier to import the code into a new base project to save the effort.
Checking 3rd Party Libraries
Checking 3rd Party Libraries
Checking 3rd Party Libraries
Checking 3rd Party Libraries
The libraries
Works fine, no illegal code.
Jet S3 libraryhttps://jets3t.dev.java.net/
The libraries
Works fine, no illegal code.
Jet S3 libraryhttps://jets3t.dev.java.net/
...except you don't need it now!
SimpleDB => HardDB
Java Library for Amazon SimpleDB - Full featured library, if somewhat over engineered.- Creates all request strings - Uses Apache commons libraries.- developer: Elena@AWS [Used by my application] 'Simple' SimpleDB code in single Java file/class (240 lines) - Very simple - Assumes user creates request strings.- developer: ian schumacher
SimpleDB = HardDB
1. Java Library for Amazon SimpleDB - Full featured library, if somewhat over engineered.- Creates all request strings - Uses Apache commons libraries.- Elena@AWS [Used by my application] 2. 'Simple' SimpleDB code in single Java file/class (240 lines) - Very simple - Assumes user creates request strings.- ianschumacher
Both fail illegal code test. option 1 fails as Apache libraries uses socket connections that are called in code.
option 2 can be fixed with modification of base64 encoding
SimpleDB = HardDB
The SimpleDB library option was abandoned as there was no reasonable hope of rebuilding and modifying the Apache libraries to work.
In addition, my project used the older SimpleDB API which required threading for performance.
The 'simple' SimpleDB code was not used because it would require creating a new library around that core.
There are no other library solutions that can be used out of the box with AppEngineJava
SimpleDB = HardDB
Decision was made to go with Google DataStore
Google DataStore
A repository that stores data objects and that can be queried like a database.
A PersistanceManager handles the CRUD operations.
Very easy to implement.
Google DataStore
Limitations:
Similar to SimpleDBQuery options are even more limited than SimpleDB, but sufficient. (e.g. no logical NOT)
Summary:Check that your application can live with the AppEngine sandbox and timeout limitations
AppEngineJava != Java. AppEngineJava has language restrictions
Try to use OSS and import libraries
Create the GWT as a fresh project and import the old project, possibly renaming the entrypoint class.
Amazon S3 is fine - but do you need it?
Amazon SimpleDB - needs a AppEngineJava friendly library - seriously consider DataStore instead in this case.
