[kujenga]

waprin's comments are on the nose with what we've experienced.

There are pain points with the flexible environment that we don't have to worry about at all with standard runtimes. The two biggest ones for us are slower deployments and a lack of monitoring tools.

Just today we actually switched one of our App Engine modules to Flexible runtimes out of necessity as we we're hitting quotas for App Engine infrastructure, and in doing so we no longer have easy access to metrics on how many instances are running or memory usage for the service. The "Cloud Trace" tools are also impaired when you aren't using standard runtimes. In short, you lose visibility into your instances. It ends up being a tradeoff between developer time and cost.

With certain runtimes in the flexible environment, you also lose out on pieces of the App Engine infrastructure like memcache, which are invaluable in optimizing services.

[gbin]

We preload a memcache proxy on your VMs for your non-gae runtimes:

https://github.com/GoogleCloudPlatform/appengine-sidecars-do...

In a nutshell, you can use a standard memcache library from your favorite language.

Disclosure: original author of this proxy when I was on the App Engine team.

[alooPotato]

Ahhh yes we've been hit with this. There are subtle differences in the GAE APIs when using flex. Trace as you mentioned, but also channels api doesn't work at all, cloud debugger only sometimes works, etc.

Most of these have gotten a lot better since managed vm's first rolled out (3 years ago!?!?!?!?!)