Hi

We've been seeing a repeat issue since we started using GAE, which is so 
infrequent that we've not ever dedicated much time to looking at it, until 
now.

Very infrequently (maybe once every couple of weeks), users are receiving 
the following message when attempting to load pages:

"Error: Server Error. The server encountered an error and could not 
complete your request. Please try again in 30 seconds."

Approx 30 seconds later, everything returns to normal and requests go 
through successfully.  Side note; we get this same message when we "gcloud 
app deploy -v [CURRENT_SERVING_VERSION]".

We've found that at the same time this error appears, our GAE dashboard > 
'Instances' graph for the service/version shows that the 'Active' instance 
count goes from 0 to 1.  It then drops down to 0 again within 2 to 5 
minutes.  On the same graph, the "Created" instance count is always 1.

The graph shows that the Active instance count does bounce up to 1 briefly 
several times per day, although I assume users don't experience (or don't 
report) the error due to their sporadic nature of use.

We can't find anything in the GCP docs that details the difference between 
a 'Created' and 'Active' instance, nor can we find anything that explains 
why the 'Active' instance count changes on a manual scaling app.

To the contrary, 
https://cloud.google.com/appengine/docs/standard/php7/how-instances-are-managed 
suggests 
that manual_scaling versions use "resident instances" which "remain in 
memory and state is preserved across requests" and "Manual scaling uses 
resident instances that continuously run the specified number of instances 
irrespective of the load level".

NB:  we do not have any /_ah/start or /_ah/stop requests at any time other 
than when the instance is manually stopped/started by us (which is nowhere 
near the time the instance count changes to 'Active').

Is anybody able to explain this behavior for us, please?  We need to 
prevent it, as its currently a minor inconvenience, but some users are 
starting to get aggravated.

app.yaml =

runtime: php72
env: standard
instance_class: B2
manual_scaling:
  instances: 1

Thanks!

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  • [google-appengine... Andy Whittle

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