Set cloud build default substitution variables through a shell script

Question

I have shell script that I use in order to be able to create my resources on Google Cloud Platform.

It looks something like this:

REGION=us-east1

# Create buckets
FILES_SOURCE=${DEVSHELL_PROJECT_ID}-source-$(date +%s)
gsutil mb -c regional -l ${REGION} gs://${FILES_SOURCE}

FUNCTIONS_BUCKET=${DEVSHELL_PROJECT_ID}-functions-$(date +%s)
gsutil mb -c regional -l ${REGION} gs://${FUNCTIONS_BUCKET}

I also have a Cloud Build enabled for my project with a trigger defined inside of it. Some of the values for my substitution variables should be equal to FILES_SOURCE and FUNCTIONS_BUCKET from the script above. If I have my Cloud Build enabled prior to the execution of my shell script, is it possible to somehow assign those values (and their keys) from the shell script?

I can see that we have gcloud builds interface but it doesn't seem to have such options.

Answer 1

You must be referring to user-defined substitution variables because default substitutions are automatically defined to you by Cloud Build. With regards to gcloud builds interface, you can set --substitutions flag to specify your user-defined variables but looking at your example, it seems that those aren't fixed.

Unfortunately you won't be able to specify user-defined substitution variables if the values came from a shell script. However, there's a workaround so that your shell script variables will persist the entire build steps by saving the values on a file and then read it as you require.

You've not specified how you intend to use the variables but here's an example:

build.sh

REGION=us-east1
DEVSHELL_PROJECT_ID=sample-proj

FUNCTIONS_BUCKET=${DEVSHELL_PROJECT_ID}-functions-$(date +%s)
FILES_SOURCE=${DEVSHELL_PROJECT_ID}-source-$(date +%s)

# Store variables on a file
echo $FUNCTIONS_BUCKET > /workspace/functions-bucket &&
echo $FILES_SOURCE > /workspace/files-source
echo "Saved values."

cloudbuild.yaml

steps:

- id: "Read script and store values"
  name: 'gcr.io/cloud-builders/gcloud'
  entrypoint: 'bash'
  args: ['./build.sh']

- id: "Read Values"
  name: gcr.io/cloud-builders/gcloud
  entrypoint: 'bash'
  args:
    - -c
    - |
      # Read from "/workspace"
      echo "First we saved " $(cat /workspace/functions-bucket) &&
      echo "Then we saved " $(cat /workspace/files-source)

Note: We used /workspace because Cloud Build uses it as a working directory by default.

Reference: https://medium.com/google-cloud/how-to-pass-data-between-cloud-build-steps-de5c9ebc4cdd