How to make App Engine use Cloud Build substitute variables for environmental variables? - google-app-engine

Question

I am trying to add Cloud Build on top of my App Engine Flask app. Everything works, but for some reason, I can't access the substitution variables I declared in the trigger.
Env vars are still being fetched from app.yaml. And they are parsed literally, not as variables. When I remove it from app.yaml Python throws a NoneType error.
[Trigger][1]: https://i.stack.imgur.com/Ii6Jv.png
[App.yaml][2]: https://i.stack.imgur.com/bg646.png
runtime: python310
instance_class: F4
automatic_scaling:
max_instances: 8
env_variables:
_CONFIG_TYPE: ${_CONFIG_TYPE}
[cloudbuild][3] https://i.stack.imgur.com/jo0PN.png
steps:
- name: 'gcr.io/google.com/cloudsdktool/cloud-sdk'
entrypoint: 'bash'
args: ['-c', 'gcloud config set app/cloud_build_timeout 1600 && gcloud app deploy']
timeout: '1600s'
substitutions:
_CONFIG_TYPE: ${_CONFIG_TYPE}

Answer 1

It won't work because gcloud app deploy command start a new Cloud Build, behind the scene, to build a container with your code and to deploy it. Your env var will change anything
The solution is to perform a bash replacement, with sed for instance.
app.yaml file
runtime: python310
instance_class: F4
automatic_scaling:
max_instances: 8
env_variables:
_CONFIG_TYPE: ##_CONFIG_TYPE##
Cloud Build Step with env var usage
steps:
- name: 'gcr.io/google.com/cloudsdktool/cloud-sdk'
entrypoint: 'bash'
env-vars:
- CONFIG_TYPE: ${_CONFIG_TYPE}
args:
- '-c'
- |
sed -i "s/##_CONFIG_TYPE##/$${CONFIG_TYPE}/g" app.yaml
gcloud config set app/cloud_build_timeout 1600
gcloud app deploy
timeout: '1600s'
substitutions:
_CONFIG_TYPE: ${_CONFIG_TYPE}
Cloud Build Step without env var usage
steps:
- name: 'gcr.io/google.com/cloudsdktool/cloud-sdk'
entrypoint: 'bash'
args:
- '-c'
- |
sed -i "s/##_CONFIG_TYPE##/${_CONFIG_TYPE}/g" app.yaml
gcloud config set app/cloud_build_timeout 1600
gcloud app deploy
timeout: '1600s'
substitutions:
_CONFIG_TYPE: ${_CONFIG_TYPE}