Trigger Cloud Builds in a mono-repo

build.sh

#!/bin/sh -e
IGNORE_FILES=$(ls -p | grep -v /)
TRACKING_BUCKET="$COMMIT_STATE_BUCKET/$REPO_NAME/$BRANCH_NAME"

detect_changed_folders() {
    gsutil cp gs://$TRACKING_BUCKET/LAST_COMMIT . &> /dev/null || true
    last_commit_sha=`cat LAST_COMMIT 2> /dev/null || git rev-list --max-parents=0 HEAD`
    echo "Detecting changes from last build: $last_commit_sha"
    folders=`git diff --name-only "$last_commit_sha" | sort -u | awk 'BEGIN {FS="/"} {print $1}' | uniq`
    export changed_components=$folders
}

run_builds() {
    echo ''
    echo '__  __                         _           _ _     _  '
    echo '|  \/  |                       | |         (_) |   | |'
    echo '| \  / | ___  _ __   ___ ______| |__  _   _ _| | __| |'
    echo '| |\/| |/ _ \| '_ \ / _ \______| '_ \| | | | | |/ _` |'
    echo '| |  | | (_) | | | | (_) |     | |_) | |_| | | | (_| |'
    echo '|_|  |_|\___/|_| |_|\___/      |_.__/ \__,_|_|_|\__,_|'
    echo ''
    for component in $changed_components
    do
        if ! [[ " ${IGNORE_FILES[@]} " =~ "$component" ]]; then
            echo -e "\nBuilding $component:"
            if ! [[ -f "$component/cloudbuild.yaml" ]]; then
                echo 'Skipping... cloudbuild.yaml not found'
            else
                (cd "$component" && gcloud builds submit --config=cloudbuild.yaml --async)
            fi
        fi
    done
    echo '-------------------------------------------------'
}

update_last_commit() {
    echo "Updating latest build commit"
    echo -n "$COMMIT_SHA" > LAST_COMMIT
    gsutil cp LAST_COMMIT gs://$TRACKING_BUCKET/LAST_COMMIT
}

detect_changed_folders
run_builds
update_last_commit

cloudbuild.yaml

steps:
  - name: gcr.io/cloud-builders/git
    args: ["fetch", "--unshallow"]
  - name: gcr.io/cloud-builders/gcloud
    entrypoint: bash
    args: ["build.sh"]
    env:
      - "REPO_NAME=$REPO_NAME"
      - "BRANCH_NAME=$BRANCH_NAME"
      - "COMMIT_SHA=$COMMIT_SHA"
      - "COMMIT_STATE_BUCKET=<bucket-name>"