Google cloud - cloubduild and app variabile substitution in trigger - google-cloud-platform

Question

I'm using cloudbuild to deploy new version of my app when a new commit appears in github.
Everything is working good.
Now I'm trying to setup a variable substitution in the trigger configuration, because I want to put my version number in the trigger once, so that I can find the deployed correct version without modifying cloudbuild configuration file.
Variabile substitution works great in my cloudbuild file, for example:
(cloudbuild.yaml)
# TEST: PRINT VARIABLE IN LOG
- name: 'gcr.io/cloud-builders/gcloud'
entrypoint: 'bash'
args: ['-c', 'echo', '${_VERSION}']
# DEPLOY APP
- name: "gcr.io/cloud-builders/gcloud"
args: ["app", "deploy", "-v", "${_VERSION}", "app.yaml"]
dir: 'frontend'
timeout: "20m"
${_VERSION} is correctly replaced with the string I put into my trigger.
Now I want to obtain the same result in app.yaml file, substituting an env variabile, something like:
(app.yaml)
runtime: nodejs
env: flex
service: backend
env_variables:
VERSION: "${_VERSION}"
TEST_ENV: "read from google"
When I read TEST_ENV from my app, it works, but _VERSION is not replaced.
Any suggestion?

Answer 1

When you perform this step
# DEPLOY APP
- name: "gcr.io/cloud-builders/gcloud"
args: ["app", "deploy", "-v", "${_VERSION}", "app.yaml"]
dir: 'frontend'
timeout: "20m"
The app.yaml is provided as-is to the gcloud command, and it's not evaluated. You have to update it manually. Something like this
# REPLACE: PUT THE CORRECT VALUE IN APP.YAML FILE
- name: 'gcr.io/cloud-builders/gcloud'
entrypoint: 'bash'
args: ['-c', 'sed', "-i", "sed -i "s/\$${_VERSION}/${_VERSION}/g", 'app.yaml']
Of course if you let the
env_variables:
VERSION: "${_VERSION}"
as-is in your app.yaml file. You can change this replacement string

Answer 2

I want to add this solution in case someone has problems with the one proposed by giullade (in my case, cloudbuild gave me an error in executing the sed command).
I also changed my replacement string to one more readable and to avoid escaping the $ sign.
# Step 0: REPLACE variables in app.yaml file
- name: 'gcr.io/cloud-builders/gcloud'
entrypoint: 'bash'
dir: 'backend'
args:
- '-c'
- |
sed -i "s/__VERSION/${_VERSION}/g" app-staging.yaml
and in my app.yaml:
env_variables:
VERSION_ENV: "__VERSION"