Running WordPress on Google App Engine is possible but different from any other hosting you ever used. Stability and performance are really great but it comes at the price of flexibility. In return you get a highly scalable and robust solution for your website. After running a few months on Google App Engine platform I switched again and in this article I will tell you why.
Google App Engine
Provided as a PaaS (Platform as a Service) Google App Engine or GAE is very specialized for high volume web applications. It doesn't only share the technology on which Google services runs but also the infrastructure. The size of Googles infrastructure is only second to Amazon. At the same time Amazon provides a wide range of services for your application development Google done much of the legwork fore you when it comes to scaling and performance of your web application. As I stated above this comes with some limitations that will effect your site.
If your building a new web application or cloud service that you want to be able to grow into dynamically and only spend time on coding GAE will supply plenty of shortcuts to get there. With a free baseline and pay-as-you-go models there is no doubt this is a good platform. However you will only be able to build a web application with limitations, nothing more.
WordPress on Goggle App Engine
The main issue with running WordPress on GAE is the file system. GAE provides read only access to the file system which prevents you from running updates online, installing themes and plugins. This has to be done in your offline dev environment and then pushed to GAE as a code update. You cant use the theme editor or any other functions that manipulate files on disc.
I know your instantly thinking about media uploads. Google have solved this with a plugin that places the uploaded files in a cloud storage bucket. Still there is a problem with this if you migrate to GAE from an other provider. The uploads I already had was placed with the code files on read only storage. So I was unable to clear old media files that where no longer needed.
There is however one good thing about this when it comes to security. Even if you get a rough plugin or any other malicious code on your site it's unable to update any of your files. It can still screw up your database but your file system is safe. And compared to shared hosting the sandboxed environment of the GAE will protect you from other users bad code.
I also like to have FTP access to my WordPress sites for easy backups, getting the latest running code for my dev and much more. Here it will be a bit more complex to download all your files at ones even though it's doable.
Google App Engine is great but specialized! When you build a new web application it's great but for an application like WordPress it's not. Even running a low traffic site will cost you money because of the cloud SQL prices. If your not happy with your shared hosting and want to move up in the world I would recommend you a VPS instead. Get your own lite puddle to play in but without the limitations.
I would also like to point out that if you develop a new application on GAE there will be a compatibility issue if you want to leave later. A lot of your code will be specialized for GAE and the transition to a new environment will take time and effort.