The Web application was built on the Windows Azure platform to implement the mosaic because Windows Azure is able to easily calibrate the number of Web Role instances needed to support unpredictable traffic bursts, and it can also separately scale out back-end Worker Role instances to support a rapid regeneration of the mosaic based on new photo uploads from consumers. By employing up to 40 backend (and parallel) Worker Role instances, a new mosaic can be regenerated in approximately 10 minutes to include new photos that were uploaded since the last mosaic was constructed. Considering that a typical mosaic is more than 5 gigapixels and, if just a single instance were used it would take approximately 5 hours to generate, this speed underscores the benefit to scaling out processing in a linear fashion.
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