UnsatisfiedRequirementsError: Node on app engine flex environment

Question

I am trying to deploy app engine node service on the flex environment. Below is my configuration in app.yaml

runtime: nodejs8
env: flex

#to name a service use below syntax
service: exampleNodeApp

env_variables:
  NODE_ENV: "dev"
  PORT: 3000

skip_files: 
  .env

manual_scaling:
  instances: 1
resources:
  cpu: 1
  memory_gb: 0.5
  disk_size_gb: 10

The config is going to use the node8 image. My package.json is as below

{
  "name": "expressapp",
  "version": "1.0.0",
  "private": true,
  "main": "./bin/www",
  "scripts": {
     "start": "node ./bin/www",
   },
  "dependencies": {
      "express": "~4.16.3",
   }
}

I have tried specifying the engine also like

{
   "node": "~8.*"
}

And to see the debug logs i used

gcloud app deploy --version default1 --verbosity=debug

the error which i get is as below. Not able to resolve even after trying everything. My app runs fine on the local. Please help!

--update-- the error log

UnsatisfiedRequirementsError: Your application does not satisfy all of  the requirements for a runtime of type [nodejs8].  Please correct the errors and try again.
ERROR: (gcloud.app.deploy) Your application does not satisfy all of the requirements for a runtime of type [nodejs8].  Please correct the errors and try again.

Answer 1

Somewhat wrongly defined (not explicitly) in the google docs.

the runtime: nodejs8 is only available for the standard environment. But for the flex env env: flex only nodejs can be given as the param. The gcloud run-time builder does not have anything like nodejs8.

Still trying to figure out whats the version of node given runtime: nodejs.

will update soon.

For further reference here is how I found the solution https://github.com/GoogleCloudPlatform/nodejs-docs-samples/issues/651