In Google Cloud Platform Monitoring, is there any way to monitor memory usage by App Engine instance? I see that there is the Memory usage metric for the GAE Application resource type, but I don't see a Memory usage metric for the GAE Instance resource type.
My particular use case is that I'd like to see (and make alerts based on) memory usage per instance.
Currently there's no built-in metric to monitor per instance memory. The only way to monitor the Memory Usage within a GAE Instance is by creating a custom metric, in this link you can find more information about custom metrics.
Just remember that the amount of instances will increase according to the load, so a per instance alert shouldn't reflect the actual load of your application, that's why the memory usage is normally measured by group on the built in metric rather than per instance.