App Engine returns 502 response

TL;DR

• Configure your instance resources (CPU, Memory size, etc…) properly
• If you occur errors check Stackdriver Logging

I tried to run my docker image in Google App Engine as App Engine Flexible Environment.

Deployed my app with gcloud app deploy and then App Engine occurred 502 error like this:

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

And I looked a health check failed to spin up a VM in Stackdriver Logging.

VM health check failed

I misunderstood the error occurred in my code or Dockerfile. However, it occurs actually when creating a VM.

And I checked logs in Stackdriver Logging and finally found one of the causes that VM's disk has no space.

No space left on device

More errors...

And rust of the causes is luck of memory size.

The instance was not enough memory

I changed my app.yaml and deployed again. Please see app.yaml Configuration File

From

runtime: custom
env: flex

service: my-service
health_check:
  enable_health_check: False

To

runtime: custom
env: flex

service: my-service
health_check:
  enable_health_check: False

resources:
  cpu: 2
  memory_gb: 5
  disk_size_gb: 25

Eventually, It worked!

I missed the logs in Stackdriver Logging and spent my time for 2 days😭…

Keep in mind to check log!