I’ve been thinking about the transition of App Engine to Python 3 and have come to the conclusion that it will never happen — App Engine will eventually be deprecated in favour of Managed VMs. Let’s break this apart to see why this is.

First, consider the effort required by Google to develop App Engine. The Python runtime environment was modified to enforce the sandbox of the App Engine environment. To provide a Python 3 environment for App Engine as we know it, the Python 3 runtime would need to be modified with the same restrictions. Even imagining that this would happen for Python 3.4, the effort to upgrade to Python 3.5 would require additional effort by Google to modify the runtime.

Considering the desire to run additional languages such as Javascript (via NodeJS) or Ruby, Google is put in an untenable position if it expects to support modified runtimes for multiple versions of different languages.

Now let’s consider the rise of Docker and the development of Managed VMs. Managed VMs are built on top of Docker and provide a ‘dockerized’ platform hosting your language runtime. Managed VMs provide the auto-scaling, health-check, colocation and server upgrades that are the hallmark of App Engine while allowing the use of arbitrary runtimes within the Docker sandbox.

This diagram from the Managed VMs documentation shows the difference between the heavily modified App Engine sandbox and the more traditional environment running within a Docker container as a Managed VM.

The great thing about Managed VMs is that they still allow access to the traditional App Engine APIs such as Datastore, Memcached, Logging, Task Queues and Search. This allows you to write applications in a fashion similar to your existing App Engine projects in a Managed VM environment. You can also use the Modules API to have a portion of your application be served by requests routed to the Managed VM and other requests routed to your App Engine application.

Managed VMs also allow better insight into product costs. The VMs are deployed as Compute Engine instances, giving you the ability to monitor CPU and network usage and upgrade and downgrade your instances as you see fit.

My feeling is that as the APIs to access Google Cloud Platform are extended and enhanced to work outside of the current App Engine sandbox, Managed VMs will take over Google’s development efforts to the point where App Engine as we know it is replaced with Managed VMs. The next project I develop will be using Managed VMs from the start.