Doing IT the App Engine Way
App Engine includes an administrator interface to your webapp that can be accessed via the Web. To see it, point your browser at http://localhost:8080/_ah/admin. Figure 4 shows the interface to the datastore entries I created. The interface lets you inspect and edit each of your entries in the datastore (as well as create new ones). Each entry has been assigned a unique Key and ID value by the datastore automatically. These values are often used to retrieve a specific entry from the datastore.
With your testing complete, you're ready for deployment. To do this, follow the deployment instructions on the App Engine Web site. This involves signing up for a Google ID (you already have one if you use Gmail or Wave), selecting a unique name for your webapp and requesting a seven-digit Google App Engine Code (which you need to activate your webapp and which is sent by SMS to your cell phone). With all of that in place, upload your code to Google's cloud from your HOME directory using this command:
google_appengin/appcfg.py update myapp/
Of course, it doesn't end there. App Engine has so much more, including integration with Google's user management and login system, security enhancements, memcached integration and validation technologies, among other things. I recommend reading Using Google App Engine and Programming Google App Engine, both from O'Reilly Media (see Resources). The former is an extended tutorial introduction to App Engine using Python, and the latter is a reference that targets both the Python and Java APIs. At the time of this writing, the other technical publishers have App Engine books at an advanced stage of development (most notably Manning). Apress also has a series of Google books. Another project worth keeping an eye out for is the upcoming Google App Engine video tutorials (again) from O'Reilly Media.
As I mentioned earlier, Google lets you get started with App Engine for free. When your site becomes popular, Google asks you to pay for the hosting services it provides. The busier your site, the more you pay, and costs are pretty much in line with what you'd expect from a reasonable-size ISP. If your site traffic remains modest, you may never have to pay for App Engine's hosting service. But, do you pay in other ways? Consider the following: once your code is uploaded to App Engine, you can't retrieve it. You can update it, but you had better keep a local copy as your own backup should you wish to transfer the business logic you've embedded in your webapp to another platform. Then, there's your data. It lives in the Google cloud, and what that means really depends on whom you ask. App Engine keeps your data away from others, but you are trusting Google to mind it for you.
App Engine is built on top of open-source Linux, with Python and Java APIs, which also are both open technologies. But, these facts alone do not make App Engine open. Far from it, this is as vertically closed a system as Apple's iPad. Be aware of what you are giving up when you decide to develop for this particular “free” Google platform. If you're okay with vendor lock-in, and if you trust Google with your data and your application, Google App Engine may be for you.
The Google App Engine Download Page: code.google.com/appengine/downloads.html
A Practical Guide to Fedora and Red Hat Enterprise Linux, 5th ed., by Mark G. Sobell, Prentice-Hall, PTR, 2010: www.pearsonhighered.com/educator/product/Practical-Guide-to-Fedora-and-Red-Hat-Enterprise-Linux-A/9780137060887.page
Using Google App Engine, by Charles Severance, O'Reilly Media, 2009: oreilly.com/catalog/9780596801601
Programming Google App Engine, by Dan Sanderson, O'Reilly Media, 2009: oreilly.com/catalog/9780596522735
Paul Barry (firstname.lastname@example.org) lectures at The Institute of Technology, Carlow in Ireland. He recently completed Head First Programming, which he cowrote with David Griffiths. As he's a sucker for punishment, he's now working on Head First Python, to be published by O'Reilly Media in late 2010.
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