Google Adds Bidirectional Communications In App Engine SDK

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In its App Engine software development kit (SDK) 1.4.0 Google has added a bidirectional channel for direct communications between web servers and JavaScript running in browsers. The new feature will make it easier to build real-time, interactive applications, such as multiplayer games and chat rooms.

The bidirectional channel allows a server to push notifications to an end user with the JavaScript that is resident and running in the browser window, "eliminating the need for polling" or a chatty back and forth asking the browser if it is available to receive a message. Google spokesman called the 1.4.0 SDK its "most significant release of the year."

These are "very big features we know developers have been eagerly awaiting," stated the App Engine development team in a blog posted to the Google site Dec. 2, the day the SDK was released. Its changes may be widely adopted in collaborative applications designed to run on App Engine, they said.

With the 1.4.0 release of the SDK, offline requests in an application may run for more than 30 seconds, the previous limit. "You can now run up to 10 minutes without interruption," the staff blog said.

The current SDK also raises the size limit on an App Engine application programming interface (API), which was previously limited to 1 MB. Several APIs have been increased to a 32-MB size limit and the Mail API for outgoing attachments has been increased from 1 to 10 MB.

The SDK changes "expand the scope" of applications that can be built with App Engine. Previous limits reflected a conservative approach to what was suitable for building and running on App Engine, and it's girding itself to handle larger applications in the future, the staff said.

The App Engine now has an option of running an application with low traffic as a high priority. Instances of the application will be kept running on three servers, even if it has no traffic, so that it will be instantly available if traffic materializes, rather than needing to be launched. The three instances also allow a hardware server to fail and still have a primary server and its backup available. The option is called the Always On feature and is priced at $9 per month.

Warm Up Requests is a feature of Always On. It anticipates a need for more instances of an application and loads them on servers before traffic needs to be sent to the additional servers. The feature is also available independently for any application through an App Engine XML command.