Why in Google App Engine Always 11 secs of Latency coming only for the first requests?

Question

I am deploying my Nodejs sample app to Google App Engine Flexible env and when I am using google app engine URL which is in the form appspot.com to hit my API, it is taking around 11 secs to send response from my mobile data, but other APIs are sending response in milisecs.

Also, the time delay is only happening when I am opening my android app and sending request to the server after that all requests are taking normal time, and again delay is coming when I again open the app and send request to the server.

Edit - I found that

This can be a caused when your application is still booting up or warming up instances to serve the request and can be called as loading latency. To avoid such scenarios you can implement health check handler like readiness check so that your application will only receive traffic when its ready

That's why I checked in my Logs that readiness check is performed sometimes around 1 sec and sometimes around 200 ms

Can anyone please tell me is there anything wrong in warming up my instances because I don't think cold boot time is causing this problem.

Edit 2

I have also tried to set min_num_instances: 2 so that once loaded atleast my 2 instances will again not get boot up, but the thing is delay is again same.

Edit 3

runtime: nodejs
#vm: true
env: flex

automatic_scaling:
  min_num_instances: 2
  max_num_instances: 3

Edit 4

I am noticing a strange behaviour that when I am using this app Packet Capture to capture traffic, then all https requests (if I am not enabling SSL Proxying) and all Http requests are executing in milisecs whereas without using this app all Http/Https requests are taking 11-16 secs of delay.

I don't know how but is there any certificate kind of issue here?

Edit 5

Below I have attached Network Profiler where delay is coming 15 secs

Please Help

Answer 1

Depends on which App Engine you are using and how you setup the scaling, there's always a loading time if you don't have a ready instance to serve a request. But if you have readiness check to ensure your instance is ready (and not cold started for the request), then there shouldn't be a problem.

Can you find a loading request or any corresponding slow request in your logs? If not, then it's likely an issue with the app. If possible, instead of calling this API on your app, do it from two apps (one is already open, one is not). So you make calls from both apps and if you notice that the one that's already open is getting a response faster than the other one, that means that's a problem with the app itself. App Engine can't determine whether or not your app is pre-opened so any difference would be client side.

=== Additional information ===

In the your logs, there's no delay at all. The request enter Google and was processed within a few milliseconds. I am sure there's something application-side. Maybe your app is constructing the request URL (first request) from some other source that results in the delay? App Engine has no knowledge of whether or not your app is opened or not or whether it's sending a first request after being opened, it cannot act differently based on it. As long as your App Engine instance is ready and available, it will treat your request the same way regardless of whether or not it's your first request after the app is opened.

Answer 2

The issue is resolved now, it was happening because of network service provider which is Bharti Airtel, their DNS lookup was taking the time to resolve the hostname. After explicitly using alternative DNS like Google 8.8.8.8 the issue got completely resolved. Maybe it's a compatibility issue of Airtel with Google Cloud.