When you run a PHP website on Azure Web Apps performance can be a concern. When you use PHP frameworks like Symphony or Laravel, the complete solutions is made up from lots of PHP files that are read from the local disc all the time. But in Azure storage is build for scale and works a bit differently. Data is stored on Azure blob storage. Getting a lot of (small) files from blob storage is expensive (in time). To make this work faster to speed up the website, local cache needs to be enabled. There were some ways to configure some caching possibilities, but they were not extensive.
Luckily this gotten a lot easier with a new feature in Azure Web Apps. By using specific Application Settings variables in the configuration, it’s now very easy to setup local cache. But, you still need to know what it means to fully understand the consequences of those settings.
For more information, there is a very good instructional video on Channel, Episode 201: Azure App Service Local Cache with Cory Fowler. The documentation of using the local cache can be found on MSDN.